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HVAC System - Manual Chevrolet Express G3500

Manual HVAC System 13 illustrations ~20713 words

Fastener Tightening Specifications

ApplicationSpecification
MetricEnglish
All Actuator Screws1.9 N.m17 lb in
HVAC Control Assembly Screw2 N.m18 lb in
Vacuum Pump Assembly Bolts3 N.m27 lb in
Vacuum Tank Nuts6 N.m53 lb in

Fastener Tightening Specifications

Scheme 1

Scheme 1: Vacuum System Control Wiring Schematic
Scheme 1: Vacuum System Control Wiring Schematic

Scheme 2

Scheme 2: Primary Blower and Air Delivery Controls (C42) and Vacuum Pump (Diesel) Wiring Schematics
Scheme 2: Primary Blower and Air Delivery Controls (C42) and Vacuum Pump (Diesel) Wiring Schematics

Scheme 3

Scheme 3: Compressor Controls (C60) Wiring Schematics
Scheme 3: Compressor Controls (C60) Wiring Schematics

Scheme 4

Scheme 4: Rear HVAC (C69) with Rear Auxiliary Controls - Front Controls Wiring Schematics
Scheme 4: Rear HVAC (C69) with Rear Auxiliary Controls - Front Controls Wiring Schematics

Scheme 5

Scheme 5: Rear HVAC (C69) with Rear Auxiliary Controls - Rear Controls Wiring Schematics
Scheme 5: Rear HVAC (C69) with Rear Auxiliary Controls - Rear Controls Wiring Schematics

Scheme 6

Scheme 6: Rear HVAC (C69) with Rear Auxiliary Controls - Air Delivery Controls Wiring Schematics
Scheme 6: Rear HVAC (C69) with Rear Auxiliary Controls - Air Delivery Controls Wiring Schematics

Scheme 7

Scheme 7: Rear HVAC (C69) without Rear Auxiliary Controls - Front Controls Wiring Schematics
Scheme 7: Rear HVAC (C69) without Rear Auxiliary Controls - Front Controls Wiring Schematics

Scheme 8

Scheme 8: Rear HVAC (C69) without Rear Auxiliary Controls - Air Delivery Controls Wiring Schematics
Scheme 8: Rear HVAC (C69) without Rear Auxiliary Controls - Air Delivery Controls Wiring Schematics

Scheme 9

Scheme 9: Rear HVAC (C36 without C69) Wiring Schematics
Scheme 9: Rear HVAC (C36 without C69) Wiring Schematics

Scheme 10

Scheme 10: Coolant Heater (K08) Wiring Schematics
Scheme 10: Coolant Heater (K08) Wiring Schematics

Diagnostic Code Index

DTCDescription
DTC B0440, B0441, or B0442DTC B0440 00 Auxiliary Heater Glow Plug Circuit Low DTC B0441 00 Auxiliary Heater Glow Plug Circuit High DTC B0442 00 Auxiliary Heater Glow Plug Circuit Open
DTC B0445, B0446, or B0447DTC B0445 00 Auxiliary Heater Fuel Pump Circuit Low DTC B0446 00 Auxiliary Heater Fuel Pump Circuit High DTC B0447 00 Auxiliary Heater Fuel Pump Circuit Open
DTC B0449, B0450, B0451, or B0452DTC B0449 00 Auxiliary Heater Blower Fan Circuit Range/Performance DTC B0450 00 Auxiliary Heater Blower Fan Circuit Low DTC B0451 00 Auxiliary Heater Blower Fan Circuit High DTC B0452 00 Auxiliary Heater Blower Fan Circuit Open
DTC B0455 or B0457DTC B0455 00 Auxiliary Heater Coolant Sensor Circuit Low DTC B0457 00 Auxiliary Heater Coolant Sensor Circuit Open
DTC B0460 or B0462DTC B0460 00 Coolant Heater Overheat Sensor Circuit Low DTC B0462 00 Coolant Heater Overheat Sensor Circuit Open
DTC B0465, B0467, or B0478DTC B0465 00 Auxiliary Heater Flame Sensor Circuit Low DTC B0467 00 Auxiliary Heater Flame Sensor Circuit Open DTC B0478 00 Flame Off From Minimum Power
DTC B0481, B0482, or B0483DTC B0481 00 Overheat Detected, Software Level DTC B0482 00 Overheat Detected, Hardware Level DTC B0483 00 Overheat Possible
DTC B0484, B0485, B0486, B0488, or B048ADTC B0484 00 Auxiliary Heater Locked DTC B0485 00 Auxiliary Heater Start Counter Overrun DTC B0486 00 Auxiliary Heater Cold Blow Time Exceeded DTC B0488 00 Auxiliary Heater Overheat Counter Overrun DTC B048A 00 Auxiliary Heater Start Time Exceeded
DTC P0532 or P0533DTC P0532 Air Conditioning A/C Refrigerant Pressure Sensor Circuit Low Voltage DTC P0533 Air Conditioning A/C Refrigerant Pressure Sensor Circuit High Voltage
DTC P0645, P0646, or P0647DTC P0645 Air Conditioning (A/C) Clutch Relay Control Circuit DTC P0646 Air Conditioning (A/C) Clutch Relay Control Circuit Low Voltage DTC P0647 Air Conditioning (A/C) Clutch Relay Control Circuit High Voltage

DIAGNOSTIC CODE INDEX

Diagnostic Instructions

  1. Perform the «Diagnostic System Check - Vehicle»(/chevrolet/express-g3500/2013-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures) prior to using this diagnostic procedure.
  2. Review «Strategy Based Diagnosis»(/chevrolet/express-g3500/2013-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__strategy-based-diagnosis) for an overview of the diagnostic approach.
  3. «Diagnostic Procedure Instructions»(/chevrolet/express-g3500/2013-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__diagnostic-procedure-instructions) provides an overview of each diagnostic category.

Diagnostic Fault Information

CircuitShort to GroundOpen/High ResistanceShort to VoltageSignal Performance
Heater Glow Plug ControlB0440 00B0442 00B0441 00
Heater Glow Plug Low ReferenceB0442 00

Circuit/System Description

The fuel operated coolant heater uses a heater glow plug to increase the temperature in the combustion chamber to a temperature that will ignite the air fuel mixture. Once a stable flame has formed, the glow plug will turn OFF.

Conditions for Running the DTC

Engine is running.

Conditions for Setting the DTC

The fuel operated coolant heater has recognized out of range condition for greater than 2.5 seconds.

Action Taken When the DTC Sets

The fuel operated coolant heater is disabled.

Conditions for Clearing the DTC

  1. A current DTC will clear when the conditions for setting the DTC are no longer present.
  2. A history DTC will clear after 40 malfunction-free ignition cycles.

Reference Information

Schematic Reference

Connector End View Reference

Description and Operation

Electrical Information Reference

  1. «Circuit Testing»(/chevrolet/express-g3500/2013-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__circuit-testing)
  2. «Connector Repairs»(/chevrolet/express-g3500/2013-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__connector-repairs)
  3. «Testing for Intermittent Conditions and Poor Connections»(/chevrolet/express-g3500/2013-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures)
  4. «Wiring Repairs»(/chevrolet/express-g3500/2013-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__wiring-repairs)

Scan Tool Reference

Control Module References for scan tool information

Circuit/System Verification

Engine running, observe the scan tool Glow Plug Command parameter. When the glow plug is activated, the scan tool should display On.

Circuit/System Testing

  1. Ignition OFF, disconnect the harness connector at the glow plug.
  2. Ignition OFF, test for less than 5 ohms between the low reference circuit terminal and ground. If greater than the specified range, replace the coolant heater.
  3. Install a test lamp between the control circuit terminal and low reference circuit terminal.
  4. Ignition ON, command the glow plug ON and OFF using a scan tool. Verify the test lamp turns ON and OFF with each command. If the test lamp is always ON, test the control circuit for a short to voltage. If the circuit tests normal, replace the coolant heater. If the test lamp is always OFF, test the control circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the coolant heater.
  5. If all circuits test normal, test or replace the glow plug.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

  1. «Heater Coolant Heater Glow Plug Replacement»(/chevrolet/express-g3500/2013-2013/remont/manual-hvac-system/#heating-ventilation-and-air-conditioning)
  2. «Heater Coolant Heater Replacement»(/chevrolet/express-g3500/2013-2013/remont/manual-hvac-system/#heating-ventilation-and-air-conditioning)
  1. Perform the «Diagnostic System Check - Vehicle»(/chevrolet/express-g3500/2013-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures) prior to using this diagnostic procedure.
  2. Review «Strategy Based Diagnosis»(/chevrolet/express-g3500/2013-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__strategy-based-diagnosis) for an overview of the diagnostic approach.
  3. «Diagnostic Procedure Instructions»(/chevrolet/express-g3500/2013-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__diagnostic-procedure-instructions) provides an overview of each diagnostic category.
CircuitShort to GroundOpen/High ResistanceShort to VoltageSignal Performance
Auxiliary Heater Fuel Pump ControlB0445 00B0447 00B0446 00
Coolant Heater Fuel Pump GroundB0447 00

The fuel operated coolant heater uses a fuel pump to supply fuel to the combustion chamber.

Engine is running.

The fuel operated heater has recognized out of range condition for more than 2.5 seconds.

The fuel operated coolant heater is disabled.

  1. A current DTC will clear when the conditions for setting the DTC are no longer present.
  2. A history DTC will clear after 40 malfunction-free ignition cycles.

Schematic Reference

Connector End View Reference

Description and Operation

Electrical Information Reference

  1. «Circuit Testing»(/chevrolet/express-g3500/2013-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__circuit-testing)
  2. «Connector Repairs»(/chevrolet/express-g3500/2013-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__connector-repairs)
  3. «Testing for Intermittent Conditions and Poor Connections»(/chevrolet/express-g3500/2013-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures)
  4. «Wiring Repairs»(/chevrolet/express-g3500/2013-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__wiring-repairs)

Scan Tool Reference

Control Module References for scan tool information

Ignition ON, command the Auxiliary Heater Fuel Pump ON and OFF with the scan tool. Verify the fuel pump turns ON and OFF as commanded.

  1. Ignition OFF, disconnect the harness connector at the fuel pump.
  2. Ignition OFF, test for less than 5 ohms between the ground circuit terminal 1 and ground. If greater than the specified range, replace the coolant heater.
  3. Install a test lamp between the control circuit terminal 2 and ground circuit terminal 1.
  4. Ignition ON, command the fuel pump ON and OFF using a scan tool. Verify the test lamp turns ON and OFF with each command. If the test lamp is always ON, test the control circuit for a short to voltage. If the circuit tests normal, replace the coolant heater. If the test lamp is always OFF, test the control circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the coolant heater.
  5. If all circuits test normal, test or replace the fuel pump.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

  1. «Heater Coolant Heater Fuel Pump Replacement»(/chevrolet/express-g3500/2013-2013/remont/manual-hvac-system/#heating-ventilation-and-air-conditioning)
  2. «Heater Coolant Heater Replacement»(/chevrolet/express-g3500/2013-2013/remont/manual-hvac-system/#heating-ventilation-and-air-conditioning)
  1. Perform the «Diagnostic System Check - Vehicle»(/chevrolet/express-g3500/2013-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures) prior to using this diagnostic procedure.
  2. Review «Strategy Based Diagnosis»(/chevrolet/express-g3500/2013-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__strategy-based-diagnosis) for an overview of the diagnostic approach.
  3. «Diagnostic Procedure Instructions»(/chevrolet/express-g3500/2013-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__diagnostic-procedure-instructions) provides an overview of each diagnostic category.
CircuitShort to GroundOpen/High ResistanceShort to VoltageSignal Performance
Coolant Heater Blower Motor ControlB0450 00B0452 00B0451 00B0449 00
Coolant Heater Blower Motor GroundB0452 00

The fuel operated heater uses a coolant heater blower motor to supply oxygen onto the combustion chamber so the air fuel mixture will ignite when the glow plug is activated.

Engine is running.

The fuel operated heater has recognized out of range condition for more than 2.5 seconds.

The fuel operated coolant heater is disabled.

  1. A current DTC will clear when the conditions for setting the DTC are no longer present.
  2. A history DTC will clear after 40 malfunction-free ignition cycles.

Schematic Reference

Connector End View Reference

Description and Operation

Electrical Information Reference

  1. «Circuit Testing»(/chevrolet/express-g3500/2013-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__circuit-testing)
  2. «Connector Repairs»(/chevrolet/express-g3500/2013-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__connector-repairs)
  3. «Testing for Intermittent Conditions and Poor Connections»(/chevrolet/express-g3500/2013-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures)
  4. «Wiring Repairs»(/chevrolet/express-g3500/2013-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__wiring-repairs)

Scan Tool Reference

Control Module References for scan tool information

Ignition ON, command the Blower Motor ON and OFF with the scan tool. Verify the blower motor turns ON and OFF as commanded.

  1. Ignition OFF, disconnect the harness connector at the blower motor.
  2. Ignition OFF, test for less than 5 ohms between the low reference circuit terminal and ground. If greater than the specified range, replace the coolant heater.
  3. Install a test lamp between the control circuit terminal and low reference circuit terminal.
  4. Ignition ON, command the blower motor ON and OFF using a scan tool. Verify the test lamp turns ON and OFF with each command. If the test lamp is always ON, test the control circuit for a short to voltage. If the circuit tests normal, replace the coolant heater. If the test lamp is always OFF, test the control circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the coolant heater.
  5. If all circuits test normal, test or replace the blower motor.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

  1. «Heater Coolant Heater Blower Replacement»(/chevrolet/express-g3500/2013-2013/remont/manual-hvac-system/#heating-ventilation-and-air-conditioning)
  2. «Heater Coolant Heater Replacement»(/chevrolet/express-g3500/2013-2013/remont/manual-hvac-system/#heating-ventilation-and-air-conditioning)
  1. Perform the «Diagnostic System Check - Vehicle»(/chevrolet/express-g3500/2013-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures) prior to using this diagnostic procedure.
  2. Review «Strategy Based Diagnosis»(/chevrolet/express-g3500/2013-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__strategy-based-diagnosis) for an overview of the diagnostic approach.
  3. «Diagnostic Procedure Instructions»(/chevrolet/express-g3500/2013-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__diagnostic-procedure-instructions) provides an overview of each diagnostic category.
CircuitShort to GroundOpen/High ResistanceShort to VoltageSignal Performance
Auxiliary Heater Coolant Sensor SignalB0455 00B0457 00B0457 00
Auxiliary Heater Coolant Sensor Low ReferenceB0457 00

The fuel operated heater uses an auxiliary heater coolant sensor to measure the coolant temperature.

Engine is running.

The fuel operated heater has recognized out of range condition for more than 2.5 seconds.

The fuel operated coolant heater is disabled.

  1. A current DTC will clear when the conditions for setting the DTC are no longer present.
  2. A history DTC will clear after 40 malfunction-free ignition cycles.

Schematic Reference

Connector End View Reference

Description and Operation

Electrical Information Reference

  1. «Circuit Testing»(/chevrolet/express-g3500/2013-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__circuit-testing)
  2. «Connector Repairs»(/chevrolet/express-g3500/2013-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__connector-repairs)
  3. «Testing for Intermittent Conditions and Poor Connections»(/chevrolet/express-g3500/2013-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures)
  4. «Wiring Repairs»(/chevrolet/express-g3500/2013-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__wiring-repairs)

Scan Tool Reference

Control Module References for scan tool information

Engine running, observe the scan tool Coolant Temp. Sensor parameter. The parameter should be between 0.09-4.9 volts.

  1. Ignition OFF, disconnect the harness connector at the coolant heater temperature sensor.
  2. Ignition OFF, test for less than 5 ohms between the low reference circuit and ground. If greater than the specified range, test the low reference circuit for an open/high resistance. If the circuit tests normal, replace the coolant heater.
  3. Ignition ON, verify the scan tool Coolant Temp. Sensor parameter is greater than 4.5 volts. If less than the specified range, test the signal circuit for a short to ground. If the circuit tests normal, replace the coolant heater.
  4. Install a 3A fused jumper wire between the signal circuit and the low reference circuit. Verify the scan tool Coolant Temp. Sensor parameter is less than 0.5 volts. If greater than the specified range, test the signal circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the coolant heater.
  5. If all circuits test normal, test or replace the coolant temperature sensor.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

  1. «Heater Coolant Heater Air Temperature Sensor Replacement»(/chevrolet/express-g3500/2013-2013/remont/manual-hvac-system/#heating-ventilation-and-air-conditioning)
  2. «Heater Coolant Heater Replacement»(/chevrolet/express-g3500/2013-2013/remont/manual-hvac-system/#heating-ventilation-and-air-conditioning)
  1. Perform the «Diagnostic System Check - Vehicle»(/chevrolet/express-g3500/2013-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures) prior to using this diagnostic procedure.
  2. Review «Strategy Based Diagnosis»(/chevrolet/express-g3500/2013-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__strategy-based-diagnosis) for an overview of the diagnostic approach.
  3. «Diagnostic Procedure Instructions»(/chevrolet/express-g3500/2013-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__diagnostic-procedure-instructions) provides an overview of each diagnostic category.
CircuitShort to GroundOpen/High ResistanceShort to VoltageSignal Performance
Coolant Heater Overheat Sensor SignalB0460 00B0462 00B0462 00
Coolant Heater Overheat Sensor Low ReferenceB0460 00

The fuel operated coolant heater uses a overheat sensor to protect the unit for over temperature condition.

Engine is running.

The fuel operated coolant heater has recognized out of range condition for more than 2.5 seconds.

The fuel operated coolant heater is disabled.

  1. A current DTC will clear when the conditions for setting the DTC are no longer present.
  2. A history DTC will clear after 40 malfunction-free ignition cycles.

Schematic Reference

Connector End View Reference

Description and Operation

Electrical Information Reference

  1. «Circuit Testing»(/chevrolet/express-g3500/2013-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__circuit-testing)
  2. «Connector Repairs»(/chevrolet/express-g3500/2013-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__connector-repairs)
  3. «Testing for Intermittent Conditions and Poor Connections»(/chevrolet/express-g3500/2013-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures)
  4. «Wiring Repairs»(/chevrolet/express-g3500/2013-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__wiring-repairs)

Scan Tool Reference

Control Module References for scan tool information

Engine running, observe the scan tool Overheat Temperature Sensor parameter. The parameter should be between 0.09-4.9 volts.

  1. Ignition OFF, disconnect the harness connector at the coolant heater temperature sensor.
  2. Ignition OFF, test for less than 5 ohms between the low reference circuit and ground. If greater than the specified range, test the low reference circuit for an open/high resistance. If the circuit tests normal, replace the coolant heater.
  3. Ignition ON, verify the scan tool Overheat Temperature Sensor parameter is greater than 4.5 volts. If less than the specified range, test the signal circuit for a short to ground. If the circuit tests normal, replace the coolant heater.
  4. Install a 3A fused jumper wire between the signal circuit and the low reference circuit. Verify the scan tool Overheat Temperature Sensor parameter is less than 0.5 volts. If greater than the specified range, test the signal circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the coolant heater.
  5. If all circuits test normal, test or replace the coolant temperature sensor.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

  1. «Heater Coolant Heater Air Temperature Sensor Replacement»(/chevrolet/express-g3500/2013-2013/remont/manual-hvac-system/#heating-ventilation-and-air-conditioning)
  2. «Heater Coolant Heater Replacement»(/chevrolet/express-g3500/2013-2013/remont/manual-hvac-system/#heating-ventilation-and-air-conditioning)
  1. Perform the «Diagnostic System Check - Vehicle»(/chevrolet/express-g3500/2013-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures) prior to using this diagnostic procedure.
  2. Review «Strategy Based Diagnosis»(/chevrolet/express-g3500/2013-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__strategy-based-diagnosis) for an overview of the diagnostic approach.
  3. «Diagnostic Procedure Instructions»(/chevrolet/express-g3500/2013-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__diagnostic-procedure-instructions) provides an overview of each diagnostic category.
CircuitShort to GroundOpen/High ResistanceShort to VoltageSignal Performance
Coolant Heater Combustion Sensor SignalB0465 00B0467 00B0467 00
Coolant Heater Combustion Sensor Low ReferenceB0467 00

The fuel operated coolant heater uses a combustion sensor to monitor flame temperature.

Engine is running.

The fuel operated coolant heater has recognized out of range condition for more than 2.5 seconds.

The fuel operated coolant heater is disabled.

  1. A current DTC will clear when the conditions for setting the DTC are no longer present.
  2. A history DTC will clear after 40 malfunction-free ignition cycles.

Schematic Reference

Connector End View Reference

Description and Operation

Electrical Information Reference

  1. «Circuit Testing»(/chevrolet/express-g3500/2013-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__circuit-testing)
  2. «Connector Repairs»(/chevrolet/express-g3500/2013-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__connector-repairs)
  3. «Testing for Intermittent Conditions and Poor Connections»(/chevrolet/express-g3500/2013-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures)
  4. «Wiring Repairs»(/chevrolet/express-g3500/2013-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__wiring-repairs)

Scan Tool Reference

Control Module References for scan tool information

  1. Ignition ON, verify DTC B1424 is not set. If the DTC is set, refer to .
  2. Engine running, observe the scan tool Flame Temperature Sensor parameter. The parameter should be between 0.09-4.9 volts.
  1. Ignition OFF, disconnect the harness connector at the combustion sensor.
  2. Ignition OFF, test for less than 5 ohms between the low reference circuit and ground. If greater than the specified range, test the low reference circuit for an open/high resistance. If the circuit tests normal, replace the coolant heater.
  3. Ignition ON, verify the scan tool Flame Temperature Sensor parameter is greater than 4.5 volts. If less than the specified range, test the signal circuit for a short to ground. If the circuit tests normal, replace the coolant heater.
  4. Install a 3A fused jumper wire between the signal circuit and the low reference circuit. Verify the scan tool Flame Temperature Sensor parameter is less than 0.5 volts. If greater than the specified range, test the signal circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the coolant heater.
  5. If all circuits test normal, test or replace the combustion sensor.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

  1. «Heater Coolant Heater Combustion Sensor Replacement»(/chevrolet/express-g3500/2013-2013/remont/manual-hvac-system/#heating-ventilation-and-air-conditioning)
  2. «Heater Coolant Heater Replacement»(/chevrolet/express-g3500/2013-2013/remont/manual-hvac-system/#heating-ventilation-and-air-conditioning)
  1. Perform the «Diagnostic System Check - Vehicle»(/chevrolet/express-g3500/2013-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures) prior to using this diagnostic procedure.
  2. Review «Strategy Based Diagnosis»(/chevrolet/express-g3500/2013-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__strategy-based-diagnosis) for an overview of the diagnostic approach.
  3. «Diagnostic Procedure Instructions»(/chevrolet/express-g3500/2013-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__diagnostic-procedure-instructions) provides an overview of each diagnostic category.

The fuel operated heater uses a coolant heater overheat sensor to protect the unit for over temperature conditions. The fuel operated heater also uses overheat detection software.

Engine is running.

The fuel operated heater has recognized an over temperature condition.

The fuel operated coolant heater is disabled.

  1. A current DTC will clear when the conditions for setting the DTC are no longer present.
  2. A history DTC will clear after 40 malfunction-free ignition cycles.

Schematic Reference

Connector End View Reference

Description and Operation

Electrical Information Reference

  1. «Circuit Testing»(/chevrolet/express-g3500/2013-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__circuit-testing)
  2. «Connector Repairs»(/chevrolet/express-g3500/2013-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__connector-repairs)
  3. «Testing for Intermittent Conditions and Poor Connections»(/chevrolet/express-g3500/2013-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures)
  4. «Wiring Repairs»(/chevrolet/express-g3500/2013-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__wiring-repairs)

Scan Tool Reference

Control Module References for scan tool information

  1. Ignition ON, verify DTC B0460 or B0462 is not set. If either DTC is set, refer to «DTC B0460 or B0462»(/chevrolet/express-g3500/2013-2013/remont/manual-hvac-system/#hvac-system-manual) .
  2. If all circuits test normal, replace the coolant heater.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

  1. Perform the «Diagnostic System Check - Vehicle»(/chevrolet/express-g3500/2013-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures) prior to using this diagnostic procedure.
  2. Review «Strategy Based Diagnosis»(/chevrolet/express-g3500/2013-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__strategy-based-diagnosis) for an overview of the diagnostic approach.
  3. «Diagnostic Procedure Instructions»(/chevrolet/express-g3500/2013-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__diagnostic-procedure-instructions) provides an overview of each diagnostic category.

The coolant heater function is to provide additional heat to the passenger compartment. The coolant heater burns diesel fuel, to heat up the engine coolant when the vehicle is running and will only operate during conditions where ambient temperature is below 4°C (39°F) and a fuel tank level greater than 12.5 percent. The heat of the hot engine coolant is transferred to the HVAC module to heat the passenger compartment. The coolant heater does not heat up instantly. It must go through a self test and start up procedure before normal operation. The vehicle must be running to start the unit but after the unit is no longer commanded on a two minute shut down (purge) procedure starts. The coolant flow is from the engine to the fuel operated heater through the heat exchanger back to the engine. Battery voltage and ground is supplied to the coolant heater. The electronic control unit inside the coolant heater determines when the unit will turn ON and OFF as well as how it will function. The electronic control unit also uses GMLAN communication and the engine control module (ECM) to transfer coolant heater information that the scan tool can read. The fuel operated heater contains flame sensors to disable the glow plug once the flame is established or to abort the startup attempt if the flame is not established.

Engine is running.

Before every start of the heater, the operation of the individual components is tested.

The fuel operated coolant heater is disabled.

  1. A current DTC will clear when the conditions for setting the DTC are no longer present.
  2. A history DTC will clear after 40 malfunction-free ignition cycles.

Schematic Reference

Connector End View Reference

Description and Operation

Electrical Information Reference

  1. «Circuit Testing»(/chevrolet/express-g3500/2013-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__circuit-testing)
  2. «Connector Repairs»(/chevrolet/express-g3500/2013-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__connector-repairs)
  3. «Testing for Intermittent Conditions and Poor Connections»(/chevrolet/express-g3500/2013-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures)
  4. «Wiring Repairs»(/chevrolet/express-g3500/2013-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__wiring-repairs)

Scan Tool Reference

Control Module References for scan tool information

  1. Ignition ON, verify DTC B0460 or B0462 is not set. If either DTC is set, refer to «DTC B0460 or B0462»(/chevrolet/express-g3500/2013-2013/remont/manual-hvac-system/#hvac-system-manual) .
  2. If all circuits test normal, replace the coolant heater.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

  1. Perform the «Diagnostic System Check - Vehicle»(/chevrolet/express-g3500/2013-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures) prior to using this diagnostic procedure.
  2. Review «Strategy Based Diagnosis»(/chevrolet/express-g3500/2013-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__strategy-based-diagnosis) for an overview of the diagnostic approach.
  3. «Diagnostic Procedure Instructions»(/chevrolet/express-g3500/2013-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__diagnostic-procedure-instructions) provides an overview of each diagnostic category.
CircuitShort to GroundOpen/High ResistanceShort to VoltageSignal Performance
5-Volt ReferenceP0532P0532
A/C Refrigerant Pressure Sensor SignalP0532P0532P0533
Low ReferenceP0533

The engine control module (ECM) monitors the high side refrigerant pressure through the A/C refrigerant pressure sensor. The ECM supplies a 5-volt reference and a low reference to the sensor. Changes in the A/C refrigerant pressure cause the sensor signal to the ECM to vary. When the pressure is high, the signal voltage is high. When the pressure is low, the signal voltage is low. When pressure is high, the ECM commands the cooling fans on. When pressure is too high or too low, the ECM will not allow the A/C compressor clutch to engage.

  1. Engine is running.
  2. Any of the conditions for setting the DTC are met for 15 seconds.
  3. Battery voltage is between 11-18 volts.
  1. The ECM detects that the A/C pressure is less than 1 psi (0.01 volt) sets DTC P0532.
  2. The ECM detects that the A/C pressure is more than 428 psi (4.92 volts) sets DTC P0533.
  1. The ECM will not illuminate the malfunction indicator lamp (MIL).
  2. The ECM stores the Failure Records.
  3. The A/C compressor clutch is disabled.
  1. The history DTC will clear after 40 consecutive ignition cycles have occurred without a malfunction.
  2. The DTC will become history if the ECM no longer detects a failure.

Diagnostic Aids

A malfunction within the refrigerant system causing high pressure can cause this DTC to set.

Schematic Reference

Connector End View Reference

Description and Operation

  1. «Air Delivery Description and Operation»(/chevrolet/express-g3500/2013-2013/remont/manual-hvac-system/#hvac-system-manual__air-delivery-description-and-operation)
  2. «Air Temperature Description and Operation»(/chevrolet/express-g3500/2013-2013/remont/manual-hvac-system/#hvac-system-manual__air-temperature-description-and-operation)

Electrical Information Reference

  1. «Circuit Testing»(/chevrolet/express-g3500/2013-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__circuit-testing)
  2. «Connector Repairs»(/chevrolet/express-g3500/2013-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__connector-repairs)
  3. «Testing for Intermittent Conditions and Poor Connections»(/chevrolet/express-g3500/2013-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures)
  4. «Wiring Repairs»(/chevrolet/express-g3500/2013-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__wiring-repairs)

Scan Tool Reference

Control Module References for scan tool information

Ignition ON, observe the scan tool A/C Refrigerant Pressure Sensor parameter. The reading should be between 0.1 volts (1 psi) and 4.90 volts (425 psi) and change with A/C refrigerant pressure changes.

Ignition ON, observe the scan tool A/C Pressure Sensor parameter. The reading should be between 0.1 volts (1 psi) and 4.90 volts (425 psi) and change with A/C refrigerant pressure changes.

  1. Ignition OFF, disconnect the harness connector at the A/C refrigerant pressure sensor.
  2. Ignition OFF, test for less than 10 ohms between the low reference circuit terminal 1 and ground. If greater than the specified range, test the low reference circuit for an open/high resistance. If the circuit tests normal, replace the ECM.
  3. Ignition ON, test for 4.8-5.2 volts between the 5-volt reference circuit terminal 2 and ground. If less than the specified range, test the 5-volt reference circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the ECM. If greater than the specified range, test the 5-volt reference circuit for a short to voltage. If the circuit tests normal, replace the ECM.
  4. Verify the scan tool A/C High Side Pressure Sensor parameter is less than 0.1 volts (1 psi). If greater than the specified range, test the signal circuit terminal 3 for a short to voltage. If the circuit tests normal, replace the ECM.
  5. Install a 3A fused jumper wire between the signal circuit terminal 3 and the 5-volt reference circuit terminal 2. Verify the scan tool A/C High Side Pressure Sensor parameter is greater than 4.90 volts (425 psi). If less than the specified range, test the signal circuit for short to ground or an open/high resistance. If the circuit tests normal, replace the ECM.
  6. If all circuits test normal, test or replace the A/C refrigerant pressure sensor.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

  1. «Air Conditioning (A/C) Refrigerant Pressure Sensor Replacement (L96)»(/chevrolet/express-g3500/2013-2013/remont/manual-hvac-system/#heating-ventilation-and-air-conditioning)
  2. «Control Module References»(/chevrolet/express-g3500/2013-2013/remont/communication-devices/#programming-and-setup-all-systems__control-module-references) for the ECM replacement, setup, and programming
  1. Perform the «Diagnostic System Check - Vehicle»(/chevrolet/express-g3500/2013-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures) prior to using this diagnostic procedure.
  2. Review «Strategy Based Diagnosis»(/chevrolet/express-g3500/2013-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__strategy-based-diagnosis) for an overview of the diagnostic approach.
  3. «Diagnostic Procedure Instructions»(/chevrolet/express-g3500/2013-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__diagnostic-procedure-instructions) provides an overview of each diagnostic category.
CircuitShort to GroundOpen/High ResistanceShort to VoltageSignal Performance
A/C Relay Coil Ignition22
A/C Relay Switch B+22
A/C Compressor Clutch Relay ControlP0645, P0646P0645, P0647P0645, P0647
A/C Relay Controlled Output221
A/C Compressor Clutch Ground22
1. A/C Clutch Always Engaged 2. A/C Clutch Inoperative

Ignition 3 voltage is supplied to the mode switch from the blower motor switch. The blower motor switch must be in any position except for OFF for A/C operation. The mode switch must be in one of the following positions for an A/C request

  1. MAX A/C
  2. A/C
  3. Bi-Level
  4. Defog
  5. Defrost

Once the mode switch is in one of these positions, the mode switch applies ignition 3 voltage to the A/C high pressure switch. If the A/C high pressure switch is closed, the voltage will then be applied to the powertrain control module (PCM), for the 8.1L (RPO L18), or engine control module (ECM), for the 6.6L (RPO LLY). The voltage applied to the ECM/PCM is an A/C request signal. The PCM/ECM then monitors the voltage on the A/C low pressure switch signal. If the voltage is low near ground, then the ECM/PCM will enable the A/C compressor clutch relay. The ECM/PCM provides a ground for the relay so it can close it internal contacts.

  1. The ignition voltage is between 9 and 18 volts.
  2. The engine speed is more than 800 RPM.
  3. The ECM/PCM A/C compressor clutch relay control transitions between ON to OFF or from OFF to ON.
  1. A short to ground on the A/C compressor clutch relay control circuit.
  2. A short to voltage on the A/C compressor clutch relay control circuit.
  3. An open circuit on the A/C compressor clutch relay control circuit or relay.
  4. An internally shorted or excessively low resistance A/C clutch relay coil.
  1. The A/C clutch relay is commanded OFF.
  2. The conditions for which the DTC was set will be stored in the Failure Records data only. No information will be stored as Freeze Frame data.

The history DTC will clear after 40 fault-free ignition cycles.

Schematic Reference

Connector End View Reference

Description and Operation

  1. «Air Delivery Description and Operation»(/chevrolet/express-g3500/2013-2013/remont/manual-hvac-system/#hvac-system-manual__air-delivery-description-and-operation)
  2. «Air Temperature Description and Operation»(/chevrolet/express-g3500/2013-2013/remont/manual-hvac-system/#hvac-system-manual__air-temperature-description-and-operation)

Electrical Information Reference

  1. «Circuit Testing»(/chevrolet/express-g3500/2013-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__circuit-testing)
  2. «Connector Repairs»(/chevrolet/express-g3500/2013-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__connector-repairs)
  3. «Testing for Intermittent Conditions and Poor Connections»(/chevrolet/express-g3500/2013-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures)
  4. «Wiring Repairs»(/chevrolet/express-g3500/2013-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__wiring-repairs)

Scan Tool Reference

Control Module References for scan tool information

Ignition ON, command the A/C relay ON and OFF with a scan tool. Observe the A/C compressor operation, the A/C compressor clutch should engage and disengage when changing between the commanded states.

  1. Ignition OFF, disconnect the A/C compressor clutch relay.
  2. Verify that a test lamp illuminates between the ignition circuit terminal 86 and ground. If the test lamp does not illuminate, test the ignition circuit for a short to ground or an open/high resistance. If the circuit tests normal and the ignition circuit fuse/breaker is open, test or replace the A/C compressor clutch relay.
  3. Connect a test lamp between the ignition circuit terminal 86 and the control circuit terminal 85.
  4. Command the A/C relay ON and OFF with a scan tool. The test lamp should turn ON and OFF when changing between the commanded states. If the test lamp is always ON, test the control circuit for a short to ground. If the circuit tests normal, replace the ECM/PCM. If the test lamp is always OFF, test the control circuit for a short to voltage, or an open/high resistance. If the circuit tests normal, replace the ECM/PCM.
  5. If all circuits test normal, test or replace the A/C compressor clutch relay.

Component Testing

  1. Ignition OFF, disconnect the A/C compressor clutch relay.
  2. Test for 60-180 ohms between terminals 85 and 86. If the resistance is not within the specified range, replace the relay.
  3. Test for infinite resistance between the following terminals: 30 and 86 30 and 87 30 and 85 85 and 87 If not the specified value, replace the relay.
  4. Install a 30-amp fused jumper wire between relay terminal 85 and 12 volts. Install a jumper wire between relay terminal 86 and ground. Test for less than 2 ohms between terminals 30 and 87. If greater than the specified range, replace the relay.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

  1. «Relay Replacement (Within an Electrical Center)»(/chevrolet/express-g3500/2013-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-repair-instructions) , «Relay Replacement (Attached to Wire Harness)»(/chevrolet/express-g3500/2013-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-repair-instructions)
  2. «Control Module References»(/chevrolet/express-g3500/2013-2013/remont/communication-devices/#programming-and-setup-all-systems__control-module-references) for ECM/PCM replacement, setup, and programming

Symptoms - HVAC Systems - Manual

IMPORTANTReview the system operation in order to familiarize yourself with the system functions. Refer to the following: Air Delivery Description and Operation Air Temperature Description and Operation

Visual/Physical Inspection

  1. Inspect for aftermarket devices which could affect the operation of the HVAC System. Refer to «Checking Aftermarket Accessories»(/chevrolet/express-g3500/2013-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__checking-aftermarket-accessories) .
  2. Inspect the easily accessible or visible system components for obvious damage or conditions which could cause the symptom.
  3. Verify the A/C compressor clutch turns freely and is not seized.
  4. The A/C compressor will not operate in cold outside air temperatures. Refer to «Air Temperature Description and Operation»(/chevrolet/express-g3500/2013-2013/remont/manual-hvac-system/#hvac-system-manual__air-temperature-description-and-operation) .
  5. The following conditions may cause window fogging: Wet carpet or mats High humidity Interior water leak Blocked A/C evaporator drain tube Maximum passenger capacity Blocked body pressure relief valves
  6. Inspect the air distribution system for causes of reduced air flow: Obstructed or dirty passenger compartment air filter, if equipped Blocked or damaged air inlet or outlet vents

Intermittent

Faulty electrical connections or wiring may be the cause of intermittent conditions. Refer to Testing for Intermittent Conditions and Poor Connections .

Symptom List

Refer to a symptom diagnostic procedure from the following list in order to diagnose the symptom

  1. «Air Conditioning Compressor Malfunction»(/chevrolet/express-g3500/2013-2013/remont/manual-hvac-system/#hvac-system-manual)
  2. «Blower Motor Malfunction»(/chevrolet/express-g3500/2013-2013/remont/manual-hvac-system/#hvac-system-manual)
  3. «Auxiliary Blower Motor Malfunction (RPO C69 with Rear Controls)»(/chevrolet/express-g3500/2013-2013/remont/manual-hvac-system/#hvac-system-manual) , «Auxiliary Blower Motor Malfunction (RPO C36)»(/chevrolet/express-g3500/2013-2013/remont/manual-hvac-system/#hvac-system-manual) , «Auxiliary Blower Motor Malfunction (RPO C69 w/o Rear Controls)»(/chevrolet/express-g3500/2013-2013/remont/manual-hvac-system/#hvac-system-manual)
  4. «Air Temperature Malfunction»(/chevrolet/express-g3500/2013-2013/remont/manual-hvac-system/#hvac-system-manual)
  5. «Auxiliary Air Temperature Malfunction»(/chevrolet/express-g3500/2013-2013/remont/manual-hvac-system/#hvac-system-manual)
  6. «Air Delivery Improper»(/chevrolet/express-g3500/2013-2013/remont/manual-hvac-system/#hvac-system-manual)
  7. «Air Delivery Improper - Auxiliary»(/chevrolet/express-g3500/2013-2013/remont/manual-hvac-system/#hvac-system-manual)
  8. «Vacuum Control System Diagnostic»(/chevrolet/express-g3500/2013-2013/remont/manual-hvac-system/#hvac-system-manual__vacuum-control-system-diagnostic)
  9. «Leak Testing»(/chevrolet/express-g3500/2013-2013/remont/manual-hvac-system/#heating-ventilation-and-air-conditioning)
  10. «Defrosting Insufficient»(/chevrolet/express-g3500/2013-2013/remont/manual-hvac-system/#heating-ventilation-and-air-conditioning__defrosting-insufficient)
  11. «Noise Diagnosis - Blower Motor»(/chevrolet/express-g3500/2013-2013/remont/manual-hvac-system/#heating-ventilation-and-air-conditioning__noise-diagnosis-blower-motor)
  12. «Noise Diagnosis - Air Conditioning (A/C) System»(/chevrolet/express-g3500/2013-2013/remont/manual-hvac-system/#heating-ventilation-and-air-conditioning__noise-diagnosis-air-conditioning-ac)
  13. «Noise Diagnosis - HVAC Module»(/chevrolet/express-g3500/2013-2013/remont/manual-hvac-system/#heating-ventilation-and-air-conditioning__noise-diagnosis-hvac-module)
  14. «Odor Diagnosis»(/chevrolet/express-g3500/2013-2013/remont/manual-hvac-system/#heating-ventilation-and-air-conditioning__odor-diagnosis)
  1. Perform the «Diagnostic System Check - Vehicle»(/chevrolet/express-g3500/2013-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures) prior to using this diagnostic procedure.
  2. Review «Strategy Based Diagnosis»(/chevrolet/express-g3500/2013-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__strategy-based-diagnosis) for an overview of the diagnostic approach.
  3. «Diagnostic Procedure Instructions»(/chevrolet/express-g3500/2013-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__diagnostic-procedure-instructions) provides an overview of each diagnostic category.
CircuitShort to GroundOpen/High ResistanceShort to VoltageSignal Performance
A/C Relay Switch B+11
A/C Relay Coil B+11
A/C Request Signal111
A/C Compressor Control112
A/C Compressor Relay ControlP0645, P0646P0645, P0646P0645, P0647
A/C Compressor Ground1
1. A/C Compressor Inoperative 2. A/C Compressor Always On

Circuit System Description

When the A/C is in the MAX A/C, A/C, Bi-Level, Defog, or Defrost position, the HVAC control assembly applies voltage to the A/C request signal circuit. This input will request the body control module (BCM) send a serial data message to the engine control module (ECM) to engage the A/C compressor. The EMC will then ground the A/C compressor clutch relay control circuit, which will switch the A/C CMPRSR CLUTCH relay on. With the relay contacts closed, battery voltage is supplied to the A/C compressor clutch assembly.

The following conditions must be met in order for the ECM/PCM to engage the A/C compressor clutch

  1. Battery voltage is between 9-18 volts
  2. Engine coolant temperature (ECT) is less than 123°C (253°F)
  3. Engine speed is less than 4, 760 RPM
  4. Engine speed is more than 600 RPM
  5. A/C high side pressure is between 2929-269 kPa (425-39 psi)
  6. Throttle position is less than 100 percent
  7. Evaporator temperature is greater than 0°C (32°F)
  8. ECM/PCM does not detect excessive torque load
  9. ECM/PCM does not detect insufficient idle quality

Schematic Reference

Connector End View Reference

Description and Operation

  1. «Air Temperature Description and Operation»(/chevrolet/express-g3500/2013-2013/remont/manual-hvac-system/#hvac-system-manual__air-temperature-description-and-operation)
  2. «Air Delivery Description and Operation»(/chevrolet/express-g3500/2013-2013/remont/manual-hvac-system/#hvac-system-manual__air-delivery-description-and-operation)

Electrical Information Reference

  1. «Circuit Testing»(/chevrolet/express-g3500/2013-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__circuit-testing)
  2. «Connector Repairs»(/chevrolet/express-g3500/2013-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__connector-repairs)
  3. «Testing for Intermittent Conditions and Poor Connections»(/chevrolet/express-g3500/2013-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures)
  4. «Wiring Repairs»(/chevrolet/express-g3500/2013-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__wiring-repairs)

Scan Tool Reference

Control Module References for scan tool information

  1. Engine running, mode switch in the MAX A/C position, verify the scan tool ECM A/C Request Signal parameter is Yes. If not the specified value, refer to A/C Request Malfunction below.
  2. Command the A/C Relay ON and OFF with the scan tool. The A/C compressor clutch should engage and disengage when changing between the commanded states. If the A/C compressor clutch does not engage or does not disengage, refer to A/C Compressor Malfunction below.

A/C Request Malfunction

  1. Ignition OFF, disconnect the X3 harness connector at the HVAC control assembly.
  2. Ignition ON, verify a test lamp illuminates between the ignition circuit terminal B and ground. If the test lamp does not illuminate, test the ignition circuit for a short to ground or an open/high resistance.
  3. Ignition OFF, connect the X3 harness connector at the HVAC control assembly. Disconnect the X4 harness connector at the HVAC control assembly.
  4. Ignition ON, verify a test lamp illuminates between the signal circuit terminal 2 and ground with the mode switch in each of the following positions: MAX A/C A/C Bi-Level Defog Defrost If the test lamp does not illuminate in each of the positions, test the signal circuit for a short ground or an open/high resistance. If the circuit tests normal, test or replace the HVAC control assembly.
  5. Ignition OFF, connect the X4 harness connector at the HVAC control assembly. Disconnect the harness connector at the A/C low pressure switch.
  6. Ignition ON, test for B+ between the signal circuit terminal B and ground. If less than the specified value, test the signal circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the BCM.
  7. Install a 3A fused jumper between the signal circuit terminal B and ground. Verify the scan tool ECM A/C Request Signal parameter is Yes. If not the specified value, test the signal circuit for a short to voltage. If the circuit tests normal, replace the BCM.
  8. Install a 3A fused jumper between the signal circuit terminal B and the signal circuit terminal A. Verify the scan tool ECM A/C Request Signal parameter is Yes. If not the specified value, test the signal circuit for a short to voltage or an open/high resistance. If the circuit tests normal, test or replace the HVAC control assembly.
  9. If all circuits test normal, test or replace the A/C low pressure switch.

A/C Compressor Malfunction

  1. Ignition OFF, disconnect the A/C compressor relay.
  2. Ignition ON, verify that a test lamp does not illuminate between the control circuit terminal 87 and ground. If the test lamp illuminates, test the control circuit for a short to voltage.
  3. Verify that a test lamp illuminates between the B+ circuit terminal 85 and ground. If the test lamp does not illuminate, test the ignition circuit for a short to ground or a open/high resistance.
  4. Verify that a test lamp illuminates between the relay B+ circuit terminal 30 and ground. If the test lamp does not illuminate, test the B+ circuit for a short to ground or a open/high resistance.
  5. Ignition OFF, disconnect the harness connector at the A/C compressor clutch.
  6. Test for less than 1 ohm between the ground circuit terminal A ground. If greater than the specified range, test the ground circuit for an open/high resistance.
  7. Connect the harness connector at the A/C compressor clutch.
  8. Ignition ON, connect a 10A fused jumper wire between the B+ circuit terminal 30 and control circuit terminal 87. Verify the A/C clutch is activated. If the A/C clutch does not activate, test the control circuit for a short to ground or an open/high resistance. If the circuit tests normal, test or replace the A/C compressor clutch.
  9. Connect a test lamp between the ignition circuit terminal 85 and the control circuit terminal 86.
  10. Command the A/C Relay ON and OFF with a scan tool. The test lamp should turn ON and OFF when changing between the commanded states. If the test lamp is always ON, test the control circuit for a short to ground. If the circuit tests normal, replace the ECM. If the test lamp is always OFF, test the control circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the ECM.
  11. If all circuits test normal, test or replace the A/C compressor relay.
  1. Ignition OFF, disconnect the A/C relay.
  2. Test for 60-180 ohms between terminals 85 and 86. If the resistance is not within the specified range, replace the relay.
  3. Test for infinite resistance between the following terminals: 30 and 86 30 and 87 30 and 85 85 and 87 If not the specified value, replace the relay.
  4. Install a 30-amp fused jumper wire between relay terminal 85 and 12 volts. Install a jumper wire between relay terminal 86 and ground. Test for less than 2 ohms between terminals

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

  1. «Relay Replacement (Within an Electrical Center)»(/chevrolet/express-g3500/2013-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-repair-instructions) , «Relay Replacement (Attached to Wire Harness)»(/chevrolet/express-g3500/2013-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-repair-instructions)
  2. «Air Conditioning Cycling Switch Replacement»(/chevrolet/express-g3500/2013-2013/remont/manual-hvac-system/#heating-ventilation-and-air-conditioning)
  3. «Heater and Air Conditioning Control Replacement»(/chevrolet/express-g3500/2013-2013/remont/manual-hvac-system/#hvac-system-manual)
  4. «Air Conditioning Clutch Coil Replacement (4.3L)»(/chevrolet/express-g3500/2013-2013/remont/manual-hvac-system/#heating-ventilation-and-air-conditioning)
  5. «Control Module References»(/chevrolet/express-g3500/2013-2013/remont/communication-devices/#programming-and-setup-all-systems__control-module-references) for BCM or ECM/PCM replacement, setup, and programming
  1. Perform the «Diagnostic System Check - Vehicle»(/chevrolet/express-g3500/2013-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures) prior to using this diagnostic procedure.
  2. Review «Strategy Based Diagnosis»(/chevrolet/express-g3500/2013-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__strategy-based-diagnosis) for an overview of the diagnostic approach.
  3. «Diagnostic Procedure Instructions»(/chevrolet/express-g3500/2013-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__diagnostic-procedure-instructions) provides an overview of each diagnostic category.
CircuitShort to GroundOpen/High ResistanceShort to VoltageSignal Performance
Blower Motor Resistor Assembly B+11
HVAC Control Assembly Ignition11
Blower Motor Control112
Low Speed Control112
Medium 1 Speed Control112
Medium 2 Speed Control112
High Speed Control112
Blower Motor Resistor Assembly Ground11
Blower Motor Ground211
1. Blower Motor Inoperative 2. Blower Motor Always On

The HVAC control assembly applies voltage to the blower motor control circuit that corresponds to the selected blower speed. The resistors and the blower motor are in a series circuit. The following list represents the number of resistors in series with the blower motor per particular speed request

  1. Low speed-3 resistors
  2. Medium 1 speed-2 resistors
  3. Medium 2 speed-1 resistor

When the operator requests High speed, the HVAC control assembly applies voltage to the blower motor through the high blower motor relay.

Schematic Reference

Connector End View Reference

Description and Operation

  1. «Air Delivery Description and Operation»(/chevrolet/express-g3500/2013-2013/remont/manual-hvac-system/#hvac-system-manual__air-delivery-description-and-operation)
  2. «Air Temperature Description and Operation»(/chevrolet/express-g3500/2013-2013/remont/manual-hvac-system/#hvac-system-manual__air-temperature-description-and-operation)

Electrical Information Reference

  1. «Circuit Testing»(/chevrolet/express-g3500/2013-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__circuit-testing)
  2. «Connector Repairs»(/chevrolet/express-g3500/2013-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__connector-repairs)
  3. «Testing for Intermittent Conditions and Poor Connections»(/chevrolet/express-g3500/2013-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures)
  4. «Wiring Repairs»(/chevrolet/express-g3500/2013-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__wiring-repairs)

Scan Tool Reference

Control Module References for scan tool information

Ignition ON, mode selector set to Panel, cycle the blower motor from LOW to HIGH using the blower motor switch. The blower motor should operate in each speed position.

  1. Ignition OFF, disconnect the X2 harness connector at the HVAC control assembly.
  2. Ignition ON, verify that a test lamp illuminates between the ignition circuit terminal E and ground. If the test lamp does not illuminate, test the ignition circuit for a short to ground or an open/high resistance.
  3. Ignition OFF, connect the X2 harness connector at the HVAC control assembly. Disconnect the X1 harness connector at the HVAC control assembly.
  4. Ignition ON, cycle the mode selector through each position. Verify a test lamp illuminates between the control circuit terminal A in each mode position. If the test lamp does not illuminate in each position, test the control circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the HVAC control assembly.
  5. Ignition OFF, connect the X1 harness connector at the HVAC control assembly. Disconnect the harness connector at the blower motor resistor assembly.
  6. Test for less than 5 ohms between the ground circuit terminal C and ground. If greater than the specified range, test the ground circuit for an open/high resistance.
  7. Ignition ON, verify a test lamp illuminates between the B+ circuit terminal A and ground. If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance.
  8. Mode selector set to Panel, while changing the fan speed switch between LOW, M1, M2 and HIGH, verify that a test lamp illuminates between the appropriate control circuit terminals listed below and ground: LOW - terminal E M1 - terminal D M2 - terminal F HIGH - terminal B If the test lamp does not illuminate, test the appropriate control circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the HVAC control assembly.
  9. Ignition OFF, connect the harness connector at the blower motor resistor assembly. Disconnect the harness connector at the blower motor.
  10. Test for less than 5 ohms between the ground circuit terminal A and ground. If greater than the specified range, test the ground circuit for an open/high resistance. If the circuit tests normal, replace the blower motor resistor assembly.
  11. Ignition ON, mode selector set to Panel, connect a test lamp between the control circuit terminal B and ground circuit terminal A.
  12. Cycle the fan speed switch between LOW, M1, M2 and HIGH speeds. The test lamp should illuminate and change in intensity as the blower speed is varied. If the test lamp is always OFF, test the control circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the blower motor resistor assembly. If the test lamp illuminates but does not change intensity, test the control circuit for a short to voltage. If the circuit tests normal, replace the blower motor resistor assembly.
  13. If all circuits test normal, test or replace the blower motor.
  1. Ignition OFF, disconnect the harness connector at the blower motor.
  2. Install a 40-amp fused jumper wire between the control circuit terminal B and 12 volts. Install a jumper wire between the ground circuit terminal A and ground. Verify the blower motor activates. If the blower motor does not activate, replace the blower motor.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

  1. «Blower Motor Replacement»(/chevrolet/express-g3500/2013-2013/remont/manual-hvac-system/#heating-ventilation-and-air-conditioning)
  2. «Heater and Air Conditioning Control Replacement»(/chevrolet/express-g3500/2013-2013/remont/manual-hvac-system/#hvac-system-manual)
  3. «Blower Motor Resistor Assembly Replacement»(/chevrolet/express-g3500/2013-2013/remont/manual-hvac-system/#heating-ventilation-and-air-conditioning)
  1. Perform the «Diagnostic System Check - Vehicle»(/chevrolet/express-g3500/2013-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures) prior to using this diagnostic procedure.
  2. Review «Strategy Based Diagnosis»(/chevrolet/express-g3500/2013-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__strategy-based-diagnosis) for an overview of the diagnostic approach.
  3. «Diagnostic Procedure Instructions»(/chevrolet/express-g3500/2013-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__diagnostic-procedure-instructions) provides an overview of each diagnostic category.
CircuitShort to GroundOpen/High ResistanceShort to VoltageSignal Performance
Low Speed Auxiliary Blower Motor Relay Switch B+11
Medium Speed Auxiliary Blower Motor Relay Switch B+11
High Speed Auxiliary Blower Motor Relay Switch B+11
Low Speed Auxiliary Blower Motor Relay Coil Ignition11
Medium Speed Auxiliary Blower Motor Relay Coil Ignition11
High Speed Auxiliary Blower Motor Relay Coil Ignition11
Low Speed Auxiliary Blower Motor Relay Coil Control252
Medium Speed Auxiliary Blower Motor Relay Coil Control353
High Speed Auxiliary Blower Motor Relay Coil Control454
Low Speed Auxiliary Blower Motor Relay Switch Output Control521
Medium Speed Auxiliary Blower Motor Relay Switch Output Control531
High Speed Auxiliary Blower Motor Relay Switch Output Control541
Auxiliary Blower Motor Control511
Auxiliary Blower Motor Ground1
Auxiliary Blower Motor Switch Ground1
1. Auxiliary Blower Motor Inoperative - All Speeds 2. Auxiliary Blower Motor Inoperative - Low 3. Auxiliary Blower Motor Inoperative - Medium 4. Auxiliary Blower Motor Inoperative - High 5. Auxiliary Blower Motor Always ON

The auxiliary blower motor switch applies a ground to the appropriate auxiliary blower motor relay that corresponds to the selected blower speed. The resistors and the blower motor are in a series circuit. The following list represents the number of resistors in series with the blower motor per particular speed request

  1. Low speed, 2 resistors
  2. Medium speed, 1 resistor

When high fan speed has been selected, the blower motor switch applies a ground to the coil side of auxiliary high speed blower motor relay which energizes the relay and provides B+ voltage to the auxiliary blower motor.

Schematic Reference

Connector End View Reference

Description and Operation

  1. «Air Temperature Description and Operation»(/chevrolet/express-g3500/2013-2013/remont/manual-hvac-system/#hvac-system-manual__air-temperature-description-and-operation)
  2. «Air Delivery Description and Operation»(/chevrolet/express-g3500/2013-2013/remont/manual-hvac-system/#hvac-system-manual__air-delivery-description-and-operation)

Electrical Information Reference

  1. «Circuit Testing»(/chevrolet/express-g3500/2013-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__circuit-testing)
  2. «Connector Repairs»(/chevrolet/express-g3500/2013-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__connector-repairs)
  3. «Testing for Intermittent Conditions and Poor Connections»(/chevrolet/express-g3500/2013-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures)
  4. «Wiring Repairs»(/chevrolet/express-g3500/2013-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__wiring-repairs)

Scan Tool Reference

Control Module References for scan tool information

Ignition ON, cycle the auxiliary blower between the LOW, MED and HIGH speed positions. The blower motor should operate at the appropriate speed in each position.

  1. If the blower motor is inoperative at all speeds, refer to Blower Motor Inoperative below.
  2. If the blower motor is inoperative in only one speed or does not change speed when cycling between the speed positions, refer to Blower Motor Malfunction below.

Blower Motor Inoperative

  1. Ignition OFF, disconnect the harness connector at the auxiliary blower motor switch.
  2. Ignition OFF, test for less than 5 ohms between the ground circuit terminal B and ground. If greater than the specified range, test the ground circuit for an open/high resistance.
  3. Ignition OFF, connect the harness connector at the auxiliary blower motor switch. Disconnect the auxiliary high speed blower motor relay.
  4. Ignition ON, verify that a test lamp illuminates between the ignition circuit terminal C2 and ground. If the test lamp does not illuminate, test the ignition circuit for a short to ground or an open/high resistance. If the circuit tests normal and the ignition circuit fuse is open, test the relay coil ignition circuit at each of the auxiliary blower motor relays for a short to ground. If the circuits test normal, replace the appropriate relay.
  5. Verify that a test lamp illuminates between the B+ circuit terminal C1 and ground. If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance. If the circuit tests normal and the B+ circuit fuse is open, test the relay switch B+ circuit at each of the auxiliary blower motor relays as well as the relay switch output control circuits for a short to ground.
  6. Ignition OFF, disconnect the harness connector at the auxiliary blower motor.
  7. Test for less than 5 ohms between the ground circuit terminal A and ground. If greater than the specified range, test the ground circuit for an open/high resistance.
  8. Connect the harness connector at the auxiliary blower motor.
  9. Ignition ON, connect a 30A fused jumper wire between the B+ circuit terminal C1 and the control circuit terminal A2. Verify the auxiliary blower motor turn ON. If the auxiliary blower motor does not turn ON, test the control circuit for an open/high resistance. If the circuit tests normal, test or replace the auxiliary blower motor.
  10. If all circuits test normal, test or replace the auxiliary blower motor switch.

Blower Motor Malfunction

  1. Ignition OFF, disconnect the appropriate blower motor relay.
  2. Ignition ON, verify that a test lamp does not illuminate between the control circuit terminal A2 and ground. If the test lamp illuminates, test the control circuit for a short to voltage.
  3. Verify that a test lamp illuminates between the ignition circuit terminal C2 and ground. If the test lamp does not illuminate, test the ignition circuit for a short to ground or an open/high resistance.
  4. Verify that a test lamp illuminates between the B+ circuit terminal C1 and ground. If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance.
  5. Connect a 30A fused jumper wire between the B+ circuit terminal C1 and the control circuit terminal A2. Verify the auxiliary blower motor turn ON. If the auxiliary blower motor does not turn ON, test the control circuit for an open/high resistance. If the circuit tests normal, test or replace the auxiliary blower motor resistor assembly.
  6. Connect a test lamp between the ignition circuit terminal C2 and the control circuit terminal A1.
  7. Cycle the auxiliary blower motor switch between OFF and the appropriate speed position. The test lamp should turn ON and OFF when changing between the commanded states. If the test lamp is always ON, test the control circuit for a short to ground. If the circuit tests normal, replace the auxiliary blower motor switch. If the test lamp is always OFF, test the control circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the auxiliary blower motor switch.
  8. If all circuits test normal, test or replace the appropriate auxiliary blower motor relay.

Relay

  1. Ignition OFF, disconnect the appropriate blower motor relay.
  2. Test for 60-180 ohms between terminals 85 and 86. If the resistance is not within the specified range, replace the relay.
  3. Test for infinite resistance between the following terminals: 30 and 86 30 and 87 30 and 85 85 and 87 If not the specified value, replace the relay.
  4. Install a 30-amp fused jumper wire between relay terminal 85 and 12 volts. Install a jumper wire between relay terminal 86 and ground. Test for less than 2 ohms between terminals 30 and 87. If greater than the specified range, replace the relay.

Blower Motor

  1. Ignition OFF, disconnect the harness connector at the auxiliary blower motor.
  2. Install a 30-amp fused jumper wire between the control circuit terminal B and 12 volts. Install a jumper wire between the ground circuit terminal A and ground. Verify the auxiliary blower motor activates. If the blower motor does not activate, replace the auxiliary blower motor.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

  1. «Auxiliary Blower Switch Replacement»(/chevrolet/express-g3500/2013-2013/remont/manual-hvac-system/#hvac-system-manual)
  2. «Auxiliary Blower Motor Resistor Assembly Replacement»(/chevrolet/express-g3500/2013-2013/remont/manual-hvac-system/#heating-ventilation-and-air-conditioning)
  3. «Auxiliary Blower Motor Replacement»(/chevrolet/express-g3500/2013-2013/remont/manual-hvac-system/#heating-ventilation-and-air-conditioning)
  4. «Auxiliary Blower Motor Relay Replacement»(/chevrolet/express-g3500/2013-2013/remont/manual-hvac-system/#heating-ventilation-and-air-conditioning)
  1. Perform the «Diagnostic System Check - Vehicle»(/chevrolet/express-g3500/2013-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures) prior to using this diagnostic procedure.
  2. Review «Strategy Based Diagnosis»(/chevrolet/express-g3500/2013-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__strategy-based-diagnosis) for an overview of the diagnostic approach.
  3. «Diagnostic Procedure Instructions»(/chevrolet/express-g3500/2013-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__diagnostic-procedure-instructions) provides an overview of each diagnostic category.
CircuitShort to GroundOpen/High ResistanceShort to VoltageSignal Performance
Low Speed Auxiliary Blower Motor Relay Switch B+11
Medium Speed Auxiliary Blower Motor Relay Switch B+11
High Speed Auxiliary Blower Motor Relay Switch B+11
Low Speed Auxiliary Blower Motor Relay Coil Ignition11
Medium Speed Auxiliary Blower Motor Relay Coil Ignition11
High Speed Auxiliary Blower Motor Relay Coil Ignition11
Low Speed Auxiliary Blower Motor Relay Coil Control252
Medium Speed Auxiliary Blower Motor Relay Coil Control353
High Speed Auxiliary Blower Motor Relay Coil Control454
Low Speed Auxiliary Blower Motor Relay Switch Output Control521
Medium Speed Auxiliary Blower Motor Relay Switch Output Control531
High Speed Auxiliary Blower Motor Relay Switch Output Control541
Auxiliary Blower Motor Control511
Auxiliary Blower Motor Ground1
Auxiliary Blower Motor Switch Ground1
1. Auxiliary Blower Motor Inoperative - All Speeds 2. Auxiliary Blower Motor Inoperative - Low 3. Auxiliary Blower Motor Inoperative - Medium 4. Auxiliary Blower Motor Inoperative - High 5. Auxiliary Blower Motor Always ON

The front auxiliary HVAC control assembly applies a ground to the appropriate auxiliary blower motor relay that corresponds to the selected blower speed. The resistors and the blower motor are in a series circuit. The following list represents the number of resistors in series with the blower motor per particular speed request

  1. Low speed, 2 resistors
  2. Medium speed, 1 resistor

When high fan speed has been selected, the blower motor switch applies a ground to the coil side of auxiliary high speed blower motor relay which energizes the relay and provides B+ voltage to the auxiliary blower motor.

Schematic Reference

Connector End View Reference

Description and Operation

  1. «Air Temperature Description and Operation»(/chevrolet/express-g3500/2013-2013/remont/manual-hvac-system/#hvac-system-manual__air-temperature-description-and-operation)
  2. «Air Delivery Description and Operation»(/chevrolet/express-g3500/2013-2013/remont/manual-hvac-system/#hvac-system-manual__air-delivery-description-and-operation)

Electrical Information Reference

  1. «Circuit Testing»(/chevrolet/express-g3500/2013-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__circuit-testing)
  2. «Connector Repairs»(/chevrolet/express-g3500/2013-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__connector-repairs)
  3. «Testing for Intermittent Conditions and Poor Connections»(/chevrolet/express-g3500/2013-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures)
  4. «Wiring Repairs»(/chevrolet/express-g3500/2013-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__wiring-repairs)

Scan Tool Reference

Control Module References for scan tool information

Ignition ON, cycle the front auxiliary HVAC control assembly blower switch between the LOW, MED and HIGH speed positions. The blower motor should operate at the appropriate speed in each position.

  1. If the blower motor is inoperative at all speeds, refer to Blower Motor Inoperative below.
  2. If the blower motor is inoperative in only one speed or does not change speed when cycling between the speed positions, refer to Blower Motor Malfunction below.

Blower Motor Inoperative

  1. Ignition OFF, disconnect the harness connector at the front auxiliary HVAC control assembly.
  2. Ignition OFF, test for less than 5 ohms between the ground circuit terminal F and ground. If greater than the specified range, test the ground circuit for an open/high resistance.
  3. Ignition OFF, connect the harness connector at the front auxiliary HVAC control assembly. Disconnect the auxiliary high speed blower motor relay.
  4. Ignition ON, verify that a test lamp illuminates between the ignition circuit terminal C2 and ground. If the test lamp does not illuminate, test the ignition circuit for a short to ground or an open/high resistance. If the circuit tests normal and the ignition circuit fuse is open, test the relay coil ignition circuit at each of the auxiliary blower motor relays for a short to ground. If the circuits test normal, replace the appropriate relay.
  5. Verify that a test lamp illuminates between the B+ circuit terminal C1 and ground. If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance. If the circuit tests normal and the B+ circuit fuse is open, test the relay switch B+ circuit at each of the auxiliary blower motor relays as well as the relay switch output control circuits for a short to ground.
  6. Ignition OFF, disconnect the harness connector at the auxiliary blower motor.
  7. Test for less than 5 ohms between the ground circuit terminal A and ground. If greater than the specified range, test the ground circuit for an open/high resistance.
  8. Connect the harness connector at the auxiliary blower motor.
  9. Ignition ON, connect a 30A fused jumper wire between the B+ circuit terminal C1 and the control circuit terminal A2. Verify the auxiliary blower motor turn ON. If the auxiliary blower motor does not turn ON, test the control circuit for an open/high resistance. If the circuit tests normal, test or replace the auxiliary blower motor.
  10. If all circuits test normal, test or replace the front auxiliary HVAC control assembly.

Blower Motor Malfunction

  1. Ignition OFF, disconnect the appropriate blower motor relay.
  2. Ignition ON, verify that a test lamp does not illuminate between the control circuit terminal A2 and ground. If the test lamp illuminates, test the control circuit for a short to voltage.
  3. Verify that a test lamp illuminates between the ignition circuit terminal C2 and ground. If the test lamp does not illuminate, test the ignition circuit for a short to ground or an open/high resistance.
  4. Verify that a test lamp illuminates between the B+ circuit terminal C1 and ground. If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance.
  5. Connect a 30A fused jumper wire between the B+ circuit terminal C1 and the control circuit terminal A2. Verify the auxiliary blower motor turn ON. If the auxiliary blower motor does not turn ON, test the control circuit for an open/high resistance. If the circuit tests normal, test or replace the auxiliary blower motor resistor assembly.
  6. Connect a test lamp between the ignition circuit terminal C2 and the control circuit terminal A1.
  7. Cycle the front auxiliary HVAC control assembly blower motor switch between OFF and the appropriate speed position. The test lamp should turn ON and OFF when changing between the commanded states. If the test lamp is always ON, test the control circuit for a short to ground. If the circuit tests normal, replace the front auxiliary HVAC control assembly. If the test lamp is always OFF, test the control circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the front auxiliary HVAC control assembly.
  8. If all circuits test normal, test or replace the appropriate auxiliary blower motor relay.

Relay

  1. Ignition OFF, disconnect the appropriate blower motor relay.
  2. Test for 60-180 ohms between terminals 85 and 86. If the resistance is not within the specified range, replace the relay.
  3. Test for infinite resistance between the following terminals: 30 and 86 30 and 87 30 and 85 85 and 87 If not the specified value, replace the relay.
  4. Install a 30-amp fused jumper wire between relay terminal 85 and 12 volts. Install a jumper wire between relay terminal 86 and ground. Test for less than 2 ohms between terminals 30 and 87. If greater than the specified range, replace the relay.

Blower Motor

  1. Ignition OFF, disconnect the harness connector at the auxiliary blower motor.
  2. Install a 30-amp fused jumper wire between the control circuit terminal B and 12 volts. Install a jumper wire between the ground circuit terminal A and ground. Verify the auxiliary blower motor activates. If the blower motor does not activate, replace the auxiliary blower motor.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

  1. «Auxiliary Heater and Air Conditioning Control Replacement - Front»(/chevrolet/express-g3500/2013-2013/remont/manual-hvac-system/#hvac-system-manual)
  2. «Auxiliary Blower Motor Replacement»(/chevrolet/express-g3500/2013-2013/remont/manual-hvac-system/#heating-ventilation-and-air-conditioning)
  3. «Auxiliary Blower Motor Resistor Assembly Replacement»(/chevrolet/express-g3500/2013-2013/remont/manual-hvac-system/#heating-ventilation-and-air-conditioning)
  4. «Auxiliary Blower Motor Relay Replacement»(/chevrolet/express-g3500/2013-2013/remont/manual-hvac-system/#heating-ventilation-and-air-conditioning)
  1. Perform the «Diagnostic System Check - Vehicle»(/chevrolet/express-g3500/2013-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures) prior to using this diagnostic procedure.
  2. Review «Strategy Based Diagnosis»(/chevrolet/express-g3500/2013-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__strategy-based-diagnosis) for an overview of the diagnostic approach.
  3. «Diagnostic Procedure Instructions»(/chevrolet/express-g3500/2013-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__diagnostic-procedure-instructions) provides an overview of each diagnostic category.
CircuitShort to GroundOpen/High ResistanceShort to VoltageSignal Performance
Low Speed Auxiliary Blower Motor Relay Switch B+11
Medium Speed Auxiliary Blower Motor Relay Switch B+11
High Speed Auxiliary Blower Motor Relay Switch B+11
Low Speed Auxiliary Blower Motor Relay Coil Ignition11
Medium Speed Auxiliary Blower Motor Relay Coil Ignition11
High Speed Auxiliary Blower Motor Relay Coil Ignition11
Low Speed Auxiliary Blower Motor Relay Coil Control252
Medium Speed Auxiliary Blower Motor Relay Coil Control353
High Speed Auxiliary Blower Motor Relay Coil Control454
Low Speed Auxiliary Blower Motor Relay Switch Output Control521
Medium Speed Auxiliary Blower Motor Relay Switch Output Control531
High Speed Auxiliary Blower Motor Relay Switch Output Control541
Auxiliary Blower Motor Control511
Auxiliary Blower Motor Ground1
Auxiliary HVAC Control Assembly Ground1
Front Auxiliary HVAC Control Assembly Ground1
1. Auxiliary Blower Motor Inoperative - All Speeds 2. Auxiliary Blower Motor Inoperative - Low 3. Auxiliary Blower Motor Inoperative - Medium 4. Auxiliary Blower Motor Inoperative - High 5. Auxiliary Blower Motor Always ON

The auxiliary blower motor is able to be controlled either by the front auxiliary HVAC control assembly or the rear auxiliary HVAC control assembly. This is accomplished through the auxiliary HVAC control assembly. With the front HVAC control assembly blower switch is in the LOW, MED, or HIGH positions, the front auxiliary HVAC control assembly retains full control of the auxiliary HVAC blower motor by directly applying a ground to the blower motor switch. When the front HVAC control assembly blower switch is in the LOW, MED, or HIGH position, the rear HVAC control assembly inputs are ignored by the auxiliary HVAC control assembly.

When the front auxiliary HVAC control assembly blower switch is placed in the AUX position, control of the system is given to the rear HVAC control assembly. When the front auxiliary HVAC control assembly blower switch is placed in the AUX position, the signal circuit between the front auxiliary HVAC control assembly and the auxiliary HVAC control assembly is grounded, indicating that control should be given to the rear auxiliary HVAC control assembly.

The front auxiliary HVAC control assembly or auxiliary HVAC control assembly applies a ground to the appropriate auxiliary blower motor relay that corresponds to the selected blower speed. The resistors and the blower motor are in a series circuit. The following list represents the number of resistors in series with the blower motor per particular speed request

  1. Low speed, 2 resistors
  2. Medium speed, 1 resistor

When high fan speed has been selected, the blower motor switch applies a ground to the coil side of auxiliary high speed blower motor relay which energizes the relay and provides B+ voltage to the auxiliary blower motor.

Schematic Reference

Connector End View Reference

Description and Operation

  1. «Air Temperature Description and Operation»(/chevrolet/express-g3500/2013-2013/remont/manual-hvac-system/#hvac-system-manual__air-temperature-description-and-operation)
  2. «Air Delivery Description and Operation»(/chevrolet/express-g3500/2013-2013/remont/manual-hvac-system/#hvac-system-manual__air-delivery-description-and-operation)

Electrical Information Reference

  1. «Circuit Testing»(/chevrolet/express-g3500/2013-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__circuit-testing)
  2. «Connector Repairs»(/chevrolet/express-g3500/2013-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__connector-repairs)
  3. «Testing for Intermittent Conditions and Poor Connections»(/chevrolet/express-g3500/2013-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures)
  4. «Wiring Repairs»(/chevrolet/express-g3500/2013-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__wiring-repairs)

Scan Tool Reference

Control Module References for scan tool information

  1. Ignition ON, cycle the front auxiliary HVAC control assembly blower switch between the LOW, MED and HIGH speed positions. The blower motor should operate at the appropriate speed in each position. If the blower motor is inoperative at all speeds, refer to Blower Motor Inoperative - Front Control below. If the blower motor is inoperative in only one speed or does not change speed when cycling between the speed positions, refer to Blower Motor Malfunction - Front Contro below.
  2. Place the front auxiliary HVAC control assembly blower switch in the AUX position.
  3. Cycle the rear auxiliary HVAC control assembly blower switch between the LOW, MED and HIGH speed positions. The blower motor should operate at the appropriate speed in each position. If the blower motor is inoperative at all speeds, refer to Blower Motor Inoperative - Rear Control below. If the blower motor is inoperative in only one speed or does not change speed when cycling between the speed positions, refer to Blower Motor Malfunction - Rear Contro below.

Blower Motor Inoperative - Front Control

  1. Ignition OFF, disconnect the harness connector at the front auxiliary HVAC control assembly.
  2. Ignition OFF, test for less than 5 ohms between the ground circuit terminal B and ground. If greater than the specified range, test the ground circuit for an open/high resistance.
  3. Connect the harness connector at the front auxiliary HVAC control assembly. Disconnect the harness connector at the auxiliary HVAC control assembly.
  4. Front auxiliary HVAC control assembly blower switch in the LOW position, test for infinite resistance between the signal circuit terminal M and ground. If less than the specified value, test the signal circuit for a short to ground. If the circuit tests normal, replace the front auxiliary HVAC control assembly.
  5. Ignition OFF, connect the harness connector at the auxiliary HVAC control assembly. Disconnect the auxiliary high speed blower motor relay.
  6. Ignition ON, verify that a test lamp illuminates between the ignition circuit terminal C2 and ground. If the test lamp does not illuminate, test the ignition circuit for a short to ground or an open/high resistance. If the circuit tests normal and the ignition circuit fuse is open, test the relay coil ignition circuit at each of the auxiliary blower motor relays for a short to ground. If the circuits test normal, replace the appropriate relay.
  7. Verify that a test lamp illuminates between the B+ circuit terminal C1 and ground. If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance. If the circuit tests normal and the B+ circuit fuse is open, test the relay switch B+ circuit at each of the auxiliary blower motor relays as well as the relay switch output control circuits for a short to ground.
  8. Ignition OFF, disconnect the harness connector at the auxiliary blower motor.
  9. Test for less than 5 ohms between the ground circuit terminal A and ground. If greater than the specified range, test the ground circuit for an open/high resistance.
  10. Connect the harness connector at the auxiliary blower motor.
  11. Ignition ON, connect a 30A fused jumper wire between the B+ circuit terminal C1 and the control circuit terminal A2. Verify the auxiliary blower motor turns ON. If the auxiliary blower motor does not turn ON, test the control circuit for an open/high resistance. If the circuit tests normal, test or replace the auxiliary blower motor.
  12. If all circuits test normal, test or replace the front auxiliary HVAC control assembly.

Blower Motor Malfunction - Front Control

  1. Ignition OFF, disconnect the appropriate blower motor relay.
  2. Ignition ON, verify that a test lamp does not illuminate between the control circuit terminal A2 and ground. If the test lamp illuminates, test the control circuit for a short to voltage.
  3. Verify that a test lamp illuminates between the ignition circuit terminal C2 and ground. If the test lamp does not illuminate, test the ignition circuit for a short to ground or an open/high resistance.
  4. Verify that a test lamp illuminates between the B+ circuit terminal C1 and ground. If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance.
  5. Connect a 30A fused jumper wire between the B+ circuit terminal C1 and the control circuit terminal A2. Verify the auxiliary blower motor turn ON. If the auxiliary blower motor does not turn ON, test the control circuit for an open/high resistance. If the circuit tests normal, test or replace the auxiliary blower motor resistor assembly.
  6. Connect a test lamp between the ignition circuit terminal C2 and the control circuit terminal A1.
  7. Cycle the front auxiliary HVAC control assembly blower motor switch between OFF and the appropriate speed position. The test lamp should turn ON and OFF when changing between the commanded states. If the test lamp is always ON, test the control circuit for a short to ground. If the circuit tests normal, replace the front auxiliary HVAC control assembly. If the test lamp is always OFF, test the control circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the front auxiliary HVAC control assembly.
  8. If all circuits test normal, test or replace the appropriate auxiliary blower motor relay.

Blower Motor Inoperative - Rear Control

  1. Ignition OFF, disconnect the harness connector at the auxiliary HVAC control assembly.
  2. Test for less than 5 ohms between the ground circuit terminal H and ground. If greater than the specified range, test the ground circuit for an open/high resistance.
  3. Ignition ON, verify a test lamp illuminates between the ignition circuit terminal J and ground. If the test lamp does not illuminate, test the ignition circuit for a short to ground or an open/high resistance.
  4. Front auxiliary HVAC control assembly blower switch in the AUX position, test for less than 5 ohms between the signal circuit terminal M and ground. If greater than the specified value, test the signal circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the front auxiliary HVAC control assembly.
  5. Ignition OFF, connect the harness connector at the auxiliary HVAC control assembly. Disconnect the rear auxiliary HVAC control assembly.
  6. Ignition ON, front auxiliary HVAC control assembly blower switch in the AUX position, test for less than 5 ohms between the control circuit terminal F and ground. If greater than the specified range, test the control circuit for an open/high resistance. If the circuit tests normal, replace the auxiliary HVAC control assembly.
  7. Ignition OFF, connect the harness connector at the rear auxiliary HVAC control assembly. Disconnect the auxiliary high speed blower motor relay.
  8. Ignition ON, verify that a test lamp illuminates between the ignition circuit terminal C2 and ground. If the test lamp does not illuminate, test the ignition circuit for a short to ground or an open/high resistance. If the circuit tests normal and the ignition circuit fuse is open, test the relay coil ignition circuit at each of the auxiliary blower motor relays for a short to ground. If the circuits test normal, replace the appropriate relay.
  9. Verify that a test lamp illuminates between the B+ circuit terminal C1 and ground. If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance. If the circuit tests normal and the B+ circuit fuse is open, test the relay switch B+ circuit at each of the auxiliary blower motor relays as well as the relay switch output control circuits for a short to ground.
  10. Ignition OFF, disconnect the harness connector at the auxiliary blower motor.
  11. Test for less than 5 ohms between the ground circuit terminal A and ground. If greater than the specified range, test the ground circuit for an open/high resistance.
  12. Connect the harness connector at the auxiliary blower motor.
  13. Ignition ON, connect a 30A fused jumper wire between the B+ circuit terminal C1 and the control circuit terminal A2. Verify the auxiliary blower motor turns ON. If the auxiliary blower motor does not turn ON, test the control circuit for an open/high resistance. If the circuit tests normal, test or replace the auxiliary blower motor.
  14. If all circuits test normal, test or replace the rear auxiliary HVAC control assembly.

Blower Motor Malfunction - Rear Control

  1. Ignition OFF, disconnect the appropriate blower motor relay.
  2. Ignition ON, verify that a test lamp does not illuminate between the control circuit terminal A2 and ground. If the test lamp illuminates, test the control circuit for a short to voltage.
  3. Verify that a test lamp illuminates between the ignition circuit terminal C2 and ground. If the test lamp does not illuminate, test the ignition circuit for a short to ground or an open/high resistance.
  4. Verify that a test lamp illuminates between the B+ circuit terminal C1 and ground. If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance.
  5. Connect a 30A fused jumper wire between the B+ circuit terminal C1 and the control circuit terminal A2. Verify the auxiliary blower motor turn ON. If the auxiliary blower motor does not turn ON, test the control circuit for an open/high resistance. If the circuit tests normal, test or replace the auxiliary blower motor resistor assembly.
  6. Connect a test lamp between the ignition circuit terminal C2 and the control circuit terminal A1.
  7. Front auxiliary HVAC control assembly blower switch in the AUX position, cycle the rear auxiliary HVAC control assembly blower motor switch between OFF and the appropriate speed position. The test lamp should turn ON and OFF when changing between the commanded states. If the test lamp is always ON, test the control circuit for a short to ground. If the circuit tests normal, replace the rear auxiliary HVAC control assembly. If the test lamp is always OFF, test the control circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the rear auxiliary HVAC control assembly.
  8. If all circuits test normal, test or replace the appropriate auxiliary blower motor relay.

Relay

  1. Ignition OFF, disconnect the appropriate blower motor relay.
  2. Test for 60-180 ohms between terminals 85 and 86. If the resistance is not within the specified range, replace the relay.
  3. Test for infinite resistance between the following terminals: 30 and 86 30 and 87 30 and 85 85 and 87 If not the specified value, replace the relay.
  4. Install a 30-amp fused jumper wire between relay terminal 85 and 12 volts. Install a jumper wire between relay terminal 86 and ground. Test for less than 2 ohms between terminals 30 and 87. If greater than the specified range, replace the relay.

Blower Motor

  1. Ignition OFF, disconnect the harness connector at the auxiliary blower motor.
  2. Install a 30-amp fused jumper wire between the control circuit terminal B and 12 volts. Install a jumper wire between the ground circuit terminal A and ground. Verify the auxiliary blower motor activates. If the blower motor does not activate, replace the auxiliary blower motor.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

  1. «Auxiliary HVAC Control Processor Replacement»(/chevrolet/express-g3500/2013-2013/remont/manual-hvac-system/#hvac-system-manual)
  2. «Auxiliary Heater and Air Conditioning Control Replacement - Rear»(/chevrolet/express-g3500/2013-2013/remont/manual-hvac-system/#hvac-system-manual)
  3. «Auxiliary Heater and Air Conditioning Control Replacement - Front»(/chevrolet/express-g3500/2013-2013/remont/manual-hvac-system/#hvac-system-manual)
  4. «Auxiliary Blower Motor Replacement»(/chevrolet/express-g3500/2013-2013/remont/manual-hvac-system/#heating-ventilation-and-air-conditioning)
  5. «Auxiliary Blower Motor Resistor Assembly Replacement»(/chevrolet/express-g3500/2013-2013/remont/manual-hvac-system/#heating-ventilation-and-air-conditioning)
  6. «Auxiliary Blower Motor Relay Replacement»(/chevrolet/express-g3500/2013-2013/remont/manual-hvac-system/#heating-ventilation-and-air-conditioning)
  1. Perform the «Diagnostic System Check - Vehicle»(/chevrolet/express-g3500/2013-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures) prior to using this diagnostic procedure.
  2. Review «Strategy Based Diagnosis»(/chevrolet/express-g3500/2013-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__strategy-based-diagnosis) for an overview of the diagnostic approach.
  3. «Diagnostic Procedure Instructions»(/chevrolet/express-g3500/2013-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__diagnostic-procedure-instructions) provides an overview of each diagnostic category.
CircuitShort to GroundOpen/High ResistanceShort to VoltageSignal Performance
Air Temperature Actuator Ignition11
Air Temperature Actuator Control111
Air Temperature Actuator Ground1
1. Air Temperature Actuator Inoperative

The air temperature actuator is a 3-wire bi-directional electric motor. Ignition 3 voltage, ground and control circuits enable the actuator to operate. The control circuit uses a 0-12 volts linear-ramped signal to command the actuator movement. The 0 and 12-volt control values represent the opposite limits of the actuator range of motion. The values in between 0 and 12 volts correspond to the positions between the limits.

When the HVAC control assembly sets a commanded, or targeted, value, the control signal is set to a value between 0-12 volts. The actuator shaft rotates until the commanded position is reached.

Inspect the air temperature door and the air temperature actuator for the following conditions

  1. A misaligned air temperature actuator.
  2. Broken or binding linkages or air temperature door.
  3. An obstruction that prevents the air temperature door from operating within its full range of motion.
  4. Missing seals to the air temperature door.
  5. Misaligned seals to the air temperature door.

Schematic Reference

Connector End View Reference

Description and Operation

  1. «Air Temperature Description and Operation»(/chevrolet/express-g3500/2013-2013/remont/manual-hvac-system/#hvac-system-manual__air-temperature-description-and-operation)
  2. «Air Delivery Description and Operation»(/chevrolet/express-g3500/2013-2013/remont/manual-hvac-system/#hvac-system-manual__air-delivery-description-and-operation)

Electrical Information Reference

  1. «Circuit Testing»(/chevrolet/express-g3500/2013-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__circuit-testing)
  2. «Connector Repairs»(/chevrolet/express-g3500/2013-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__connector-repairs)
  3. «Testing for Intermittent Conditions and Poor Connections»(/chevrolet/express-g3500/2013-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures)
  4. «Wiring Repairs»(/chevrolet/express-g3500/2013-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__wiring-repairs)

Scan Tool Reference

Control Module References for scan tool information

  1. Ignition ON, engine running, place the blower motor switch at the maximum speed position and the mode switch in the vent or panel position.
  2. Rotate the temperature control switch from the full COLD position to the full HOT position. The air temperature should follow the commanded states of full HOT to full COLD.
  1. Ignition OFF, disconnect the harness connector at the air temperature actuator.
  2. Test for less than 1.0 ohm between the ground circuit terminal 7 and ground. If greater than the specified range, test the ground circuit for an open/high resistance.
  3. Ignition ON, verify that a test lamp illuminates between the ignition circuit terminal 10 and ground. If the test lamp does not illuminate, test the ignition circuit for a short to ground or an open/high resistance.
  4. Install a DMM between the control circuit terminal 8 and ground. Command the actuator in both directions. Voltage on the control circuit should change from 0 volts when commanding the actuator in one direction to 12 volts in the other direction. If the voltage does not change as specified, test the control circuit for a short to voltage, short to ground, or an open/high resistance. If the circuit tests normal, replace the HVAC control module.
  5. If all circuits test normal, test or replace the air temperature actuator.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

  1. «Temperature Valve Actuator Replacement»(/chevrolet/express-g3500/2013-2013/remont/manual-hvac-system/#hvac-system-manual)
  2. «Heater and Air Conditioning Control Replacement»(/chevrolet/express-g3500/2013-2013/remont/manual-hvac-system/#hvac-system-manual)
  1. Perform the «Diagnostic System Check - Vehicle»(/chevrolet/express-g3500/2013-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures) prior to using this diagnostic procedure.
  2. Review «Strategy Based Diagnosis»(/chevrolet/express-g3500/2013-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__strategy-based-diagnosis) for an overview of the diagnostic approach.
  3. «Diagnostic Procedure Instructions»(/chevrolet/express-g3500/2013-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__diagnostic-procedure-instructions) provides an overview of each diagnostic category.
CircuitShort to GroundOpen/High ResistanceShort to VoltageSignal Performance
Front Auxiliary HVAC Control Assembly B+11
Rear Auxiliary HVAC Control Assembly B+22
Auxiliary Air Temperature Actuator Ignition1, 21, 2
Front Auxiliary Air Temperature Signal111
Rear Auxiliary Air Temperature Signal222
Auxiliary Air Temperature Actuator Control1, 21, 21, 2
Auxiliary Air Temperature Actuator Ground1, 2
1. Auxiliary Air Temperature Control Inoperative from Front Control 2. Auxiliary Air Temperature Control Inoperative from Rear Control

The auxiliary air temperature actuator is a 3-wire bi-directional electric motor. Ignition 3 voltage, ground and control circuits enable the actuator to operate. The control circuit uses a 0-12 volts linear-ramped signal to command the actuator movement. The 0 and 12-volt control values represent the opposite limits of the actuator range of motion. The values in between 0 and 12 volts correspond to the positions between the limits.

When the HVAC control assembly sets a commanded, or targeted, value, the control signal is set to a value between 0-12 volts. The actuator shaft rotates until the commanded position is reached. The module will maintain the control value until a new commanded value is needed.

Inspect the auxiliary air temperature door and the auxiliary air temperature actuator for the following conditions

  1. A misaligned auxiliary air temperature actuator.
  2. Broken or binding linkages or auxiliary air temperature door.
  3. An obstruction that prevents the auxiliary air temperature door from operating within its full range of motion.
  4. Missing seals to the auxiliary air temperature door.
  5. Misaligned seals to the auxiliary air temperature door.

Schematic Reference

Connector End View Reference

Description and Operation

  1. «Air Temperature Description and Operation»(/chevrolet/express-g3500/2013-2013/remont/manual-hvac-system/#hvac-system-manual__air-temperature-description-and-operation)
  2. «Air Delivery Description and Operation»(/chevrolet/express-g3500/2013-2013/remont/manual-hvac-system/#hvac-system-manual__air-delivery-description-and-operation)

Electrical Information Reference

  1. «Circuit Testing»(/chevrolet/express-g3500/2013-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__circuit-testing)
  2. «Connector Repairs»(/chevrolet/express-g3500/2013-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__connector-repairs)
  3. «Testing for Intermittent Conditions and Poor Connections»(/chevrolet/express-g3500/2013-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures)
  4. «Wiring Repairs»(/chevrolet/express-g3500/2013-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__wiring-repairs)

Scan Tool Reference

Control Module References for scan tool information

With Rear Auxiliary Controls

  1. Ignition ON, cycle the front auxiliary HVAC control assembly blower switch through the LOW, MED, and HIGH speeds. The blower motor should operate at all speeds. If the blower motor is inoperative, refer to «Auxiliary Blower Motor Malfunction (RPO C69 with Rear Controls)»(/chevrolet/express-g3500/2013-2013/remont/manual-hvac-system/#hvac-system-manual) , «Auxiliary Blower Motor Malfunction (RPO C36)»(/chevrolet/express-g3500/2013-2013/remont/manual-hvac-system/#hvac-system-manual) , «Auxiliary Blower Motor Malfunction (RPO C69 w/o Rear Controls)»(/chevrolet/express-g3500/2013-2013/remont/manual-hvac-system/#hvac-system-manual) .
  2. Rotate the front auxiliary HVAC control assembly air temperature control from the full COLD position to the full HOT position. The air temperature should follow the commanded states of full HOT to full COLD. If the air temperature does not change, refer to Air Temperature Malfunction - Front Auxiliary Control below.
  3. Front auxiliary HVAC control assembly blower switch in the AUX position, cycle the rear auxiliary HVAC control assembly blower switch through the LOW, MED, and HIGH speeds. The blower motor should operate at all speeds. If the blower motor is inoperative, refer to «Auxiliary Blower Motor Malfunction (RPO C69 with Rear Controls)»(/chevrolet/express-g3500/2013-2013/remont/manual-hvac-system/#hvac-system-manual) , «Auxiliary Blower Motor Malfunction (RPO C36)»(/chevrolet/express-g3500/2013-2013/remont/manual-hvac-system/#hvac-system-manual) , «Auxiliary Blower Motor Malfunction (RPO C69 w/o Rear Controls)»(/chevrolet/express-g3500/2013-2013/remont/manual-hvac-system/#hvac-system-manual) .
  4. Rotate the rear auxiliary HVAC control assembly air temperature control from the full COLD position to the full HOT position. The air temperature should follow the commanded states of full HOT to full COLD. If the air temperature does not change, refer to Air Temperature Malfunction - Rear Auxiliary Control below.

Without Rear Auxiliary Controls

  1. Ignition ON, cycle the front auxiliary HVAC control assembly blower switch through the LOW, MED, and HIGH speeds. The blower motor should operate at all speeds. If the blower motor is inoperative, refer to «Auxiliary Blower Motor Malfunction (RPO C69 with Rear Controls)»(/chevrolet/express-g3500/2013-2013/remont/manual-hvac-system/#hvac-system-manual) , «Auxiliary Blower Motor Malfunction (RPO C36)»(/chevrolet/express-g3500/2013-2013/remont/manual-hvac-system/#hvac-system-manual) , «Auxiliary Blower Motor Malfunction (RPO C69 w/o Rear Controls)»(/chevrolet/express-g3500/2013-2013/remont/manual-hvac-system/#hvac-system-manual) .
  2. Rotate the front auxiliary HVAC control assembly air temperature control from the full COLD position to the full HOT position. The air temperature should follow the commanded states of full HOT to full COLD. If the air temperature does not change, refer to Air Temperature Malfunction without Rear Auxiliary Control below.

Air Temperature Malfunction - Front Auxiliary Control

  1. Ignition OFF, disconnect the harness connector at the front auxiliary HVAC control assembly.
  2. Ignition ON, verify a test lamp illuminates between the ignition circuit terminal J and ground. If the test lamp does not illuminate, test the ignition circuit for a short to ground or an open/high resistance.
  3. Ignition OFF, connect the harness connector at the front auxiliary HVAC control assembly. Disconnect the harness connector at the auxiliary HVAC control assembly.
  4. Ignition ON, test for ignition voltage between the signal circuit terminal A and ground. If less than the specified value, test the signal circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the front auxiliary HVAC control assembly.
  5. Ignition OFF, connect the harness connector at the auxiliary HVAC control assembly. Disconnect the harness connector at the auxiliary air temperature actuator.
  6. Test for less than 5 ohms between the ground circuit terminal 7 and ground. If greater than the specified range, test the ground circuit for an open/high resistance.
  7. Ignition ON, verify that a test lamp illuminates between the ignition circuit terminal 10 and ground. If the test lamp does not illuminate, test the ignition circuit for a short to ground or an open/high resistance.
  8. Install a DMM between the control circuit terminal 8 and ground. Command the actuator in each direction. Voltage on the control circuit should change from 0 volts when commanding the actuator in one direction to 12 volts in the other direction. If the voltage does not change as specified, replace the auxiliary HVAC control assembly.
  9. If all circuits test normal, test or replace the auxiliary air temperature actuator.

Air Temperature Malfunction - Rear Auxiliary Control

  1. Ignition OFF, disconnect the harness connector at the rear auxiliary HVAC control assembly.
  2. Test for less than 5 ohms between the ground circuit terminal B and ground. If greater than the specified range, test the ground circuit for an open/high resistance.
  3. Ignition ON, verify a test lamp illuminates between the ignition circuit terminal G and ground. If the test lamp does not illuminate, test the ignition circuit for a short to ground or an open/high resistance.
  4. Ignition OFF, connect the harness connector at the front auxiliary HVAC control assembly. Disconnect the harness connector at the auxiliary HVAC control assembly.
  5. Ignition ON, test for ignition voltage between the signal circuit terminal C and ground. If less than the specified value, test the signal circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the rear auxiliary HVAC control assembly.
  6. If all circuits test normal, replace the auxiliary HVAC control assembly.

Air Temperature Malfunction without Rear Auxiliary Control

  1. Ignition OFF, disconnect the harness connector at the front auxiliary HVAC control assembly.
  2. Ignition ON, verify a test lamp illuminates between the ignition circuit terminal G and ground. If the test lamp does not illuminate, test the ignition circuit for a short to ground or an open/high resistance.
  3. Ignition OFF, connect the harness connector at the front auxiliary HVAC control assembly. Disconnect the harness connector at the auxiliary air temperature actuator.
  4. Test for less than 5 ohms between the ground circuit terminal 7 and ground. If greater than the specified range, test the ground circuit for an open/high resistance.
  5. Ignition ON, verify that a test lamp illuminates between the ignition circuit terminal 10 and ground. If the test lamp does not illuminate, test the ignition circuit for a short to ground or an open/high resistance.
  6. Install a DMM between the control circuit terminal 8 and ground. Command the actuator in each direction. Voltage on the control circuit should change from 0 volts when commanding the actuator in one direction to 12 volts in the other direction. If the voltage does not change as specified, replace the front auxiliary HVAC control assembly.
  7. If all circuits test normal, test or replace the auxiliary air temperature actuator.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

  1. «Auxiliary Temperature Valve Actuator Replacement»(/chevrolet/express-g3500/2013-2013/remont/manual-hvac-system/#hvac-system-manual)
  2. «Auxiliary Heater and Air Conditioning Control Replacement - Front»(/chevrolet/express-g3500/2013-2013/remont/manual-hvac-system/#hvac-system-manual)
  3. «Auxiliary Heater and Air Conditioning Control Replacement - Rear»(/chevrolet/express-g3500/2013-2013/remont/manual-hvac-system/#hvac-system-manual)
  4. «Auxiliary HVAC Control Processor Replacement»(/chevrolet/express-g3500/2013-2013/remont/manual-hvac-system/#hvac-system-manual)
  1. Perform the «Diagnostic System Check - Vehicle»(/chevrolet/express-g3500/2013-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures) prior to using this diagnostic procedure.
  2. Review «Strategy Based Diagnosis»(/chevrolet/express-g3500/2013-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__strategy-based-diagnosis) for an overview of the diagnostic approach.
  3. «Diagnostic Procedure Instructions»(/chevrolet/express-g3500/2013-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__diagnostic-procedure-instructions) provides an overview of each diagnostic category.
CircuitShort to GroundOpen/High ResistanceShort to VoltageSignal Performance
Ignition11
Ground1
1. Vacuum Pump Inoperative

The HVAC control assembly uses vacuum to control the mode doors. Vehicles equipped with diesel engines use a vacuum pump to create vacuum. The vacuum pump has ignition voltage circuit and a ground circuit to operate. The pump turns on when vacuum is low and turns off when vacuum reaches 10 Hg.

Schematic Reference

Connector End View Reference

Description and Operation

  1. «Air Temperature Description and Operation»(/chevrolet/express-g3500/2013-2013/remont/manual-hvac-system/#hvac-system-manual__air-temperature-description-and-operation)
  2. «Air Delivery Description and Operation»(/chevrolet/express-g3500/2013-2013/remont/manual-hvac-system/#hvac-system-manual__air-delivery-description-and-operation)

Electrical Information Reference

  1. «Circuit Testing»(/chevrolet/express-g3500/2013-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__circuit-testing)
  2. «Connector Repairs»(/chevrolet/express-g3500/2013-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__connector-repairs)
  3. «Testing for Intermittent Conditions and Poor Connections»(/chevrolet/express-g3500/2013-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures)
  4. «Wiring Repairs»(/chevrolet/express-g3500/2013-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__wiring-repairs)

Scan Tool Reference

Control Module References for scan tool information

  1. Ignition ON, mode set to the VENT position, place the blower switch in the LO, MED 1, MED 2 and HI speed positions. The blower motor should activate and operate from low to medium 1, medium 2, to high when changing between the commanded states. If the blower motor speed does not change or fails to operate at a selected speed, refer to «Blower Motor Malfunction»(/chevrolet/express-g3500/2013-2013/remont/manual-hvac-system/#hvac-system-manual) .
  2. Rotate the mode control switch from the OFF position to the VENT, BI-LEVEL, FLOOR, FLOOR/DEFROST and DEFROST positions. The air flow should follow the commanded states and blow through the vent, floor and defrost outlets. If the air flow fails to blow through the selected outlets, refer to «Vacuum Control System Diagnostic»(/chevrolet/express-g3500/2013-2013/remont/manual-hvac-system/#hvac-system-manual__vacuum-control-system-diagnostic) .
  1. Ignition OFF, disconnect the harness connector at the vacuum pump.
  2. Test for less than 1.0 ohms between the ground circuit terminal A and ground. If greater than the specified range, test the ground circuit for an open/high resistance.
  3. Ignition ON, verify that a test lamp illuminates between the ignition circuit terminal B and ground. If the test lamp does not illuminate, test the ignition circuit for a short to ground or an open/high resistance.
  4. If all circuits test normal, test or replace the vacuum pump assembly.

Perform the Diagnostic Repair Verification after completing the repair.

  1. Perform the «Diagnostic System Check - Vehicle»(/chevrolet/express-g3500/2013-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures) prior to using this diagnostic procedure.
  2. Review «Strategy Based Diagnosis»(/chevrolet/express-g3500/2013-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__strategy-based-diagnosis) for an overview of the diagnostic approach.
  3. «Diagnostic Procedure Instructions»(/chevrolet/express-g3500/2013-2013/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__diagnostic-procedure-instructions) provides an overview of each diagnostic category.
CircuitShort to GroundOpen/High ResistanceShort to VoltageSignal Performance
Front Auxiliary HVAC Control Assembly B+11
Rear Auxiliary HVAC Control Assembly B+22
Auxiliary Mode Actuator Ignition1, 21, 2
Front Auxiliary Mode Signal111
Rear Auxiliary Mode Signal222
Auxiliary Mode Actuator Control1, 21, 21, 2
Auxiliary Mode Actuator Ground1, 2
1. Auxiliary Mode Selection Inoperative from Front Control 2. Auxiliary Mode Selection Inoperative from Rear Control

The auxiliary mode actuator is a 3-wire bi-directional electric motor. Ignition 3 voltage, ground and control circuits enable the actuator to operate. The control circuit uses a 0-12 volts linear-ramped signal to command the actuator movement. The 0 and 12-volt control values represent the opposite limits of the actuator range of motion. The values in between 0 and 12 volts correspond to the positions between the limits.

When the HVAC control assembly sets a commanded, or targeted, value, the control signal is set to a value between 0-12 volts. The actuator shaft rotates until the commanded position is reached. The module will maintain the control value until a new commanded value is needed.

Inspect the auxiliary mode door and the auxiliary mode actuator for the following conditions

  1. A misaligned auxiliary mode actuator.
  2. Broken or binding linkages or auxiliary mode door.
  3. An obstruction that prevents the auxiliary mode door from operating within its full range of motion.
  4. Missing seals to the auxiliary mode door.
  5. Misaligned seals to the auxiliary mode door.

Schematic Reference

Connector End View Reference

Description and Operation

  1. «Air Temperature Description and Operation»(/chevrolet/express-g3500/2013-2013/remont/manual-hvac-system/#hvac-system-manual__air-temperature-description-and-operation)
  2. «Air Delivery Description and Operation»(/chevrolet/express-g3500/2013-2013/remont/manual-hvac-system/#hvac-system-manual__air-delivery-description-and-operation)

Electrical Information Reference

  1. «Circuit Testing»(/chevrolet/express-g3500/2013-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__circuit-testing)
  2. «Connector Repairs»(/chevrolet/express-g3500/2013-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__connector-repairs)
  3. «Testing for Intermittent Conditions and Poor Connections»(/chevrolet/express-g3500/2013-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures)
  4. «Wiring Repairs»(/chevrolet/express-g3500/2013-2013/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__wiring-repairs)

With Rear Auxiliary Controls

  1. Ignition ON, cycle the front auxiliary HVAC control assembly blower switch through the LOW, MED, and HIGH speeds. The blower motor should operate at all speeds. If the blower motor is inoperative, refer to «Auxiliary Blower Motor Malfunction (RPO C69 with Rear Controls)»(/chevrolet/express-g3500/2013-2013/remont/manual-hvac-system/#hvac-system-manual) , «Auxiliary Blower Motor Malfunction (RPO C36)»(/chevrolet/express-g3500/2013-2013/remont/manual-hvac-system/#hvac-system-manual) , «Auxiliary Blower Motor Malfunction (RPO C69 w/o Rear Controls)»(/chevrolet/express-g3500/2013-2013/remont/manual-hvac-system/#hvac-system-manual) .
  2. Rotate the front auxiliary HVAC control assembly air temperature control from the VENT position to the FLOOR position. The mode should follow the commanded states VENT to FLOOR. If the mode does not change, refer to Mode Malfunction - Front Auxiliary Control below.
  3. Front auxiliary HVAC control assembly blower switch in the AUX position, cycle the rear auxiliary HVAC control assembly blower switch through the LOW, MED, and HIGH speeds. The blower motor should operate at all speeds. If the blower motor is inoperative, refer to «Auxiliary Blower Motor Malfunction (RPO C69 with Rear Controls)»(/chevrolet/express-g3500/2013-2013/remont/manual-hvac-system/#hvac-system-manual) , «Auxiliary Blower Motor Malfunction (RPO C36)»(/chevrolet/express-g3500/2013-2013/remont/manual-hvac-system/#hvac-system-manual) , «Auxiliary Blower Motor Malfunction (RPO C69 w/o Rear Controls)»(/chevrolet/express-g3500/2013-2013/remont/manual-hvac-system/#hvac-system-manual) .
  4. Rotate the rear auxiliary HVAC control assembly air temperature control from the VENT position to the FLOOR position. The mode should follow the commanded states VENT to FLOOR. If the mode does not change, refer to Mode Malfunction - Rear Auxiliary Control below.

Without Rear Auxiliary Controls

  1. Ignition ON, cycle the front auxiliary HVAC control assembly blower switch through the LOW, MED, and HIGH speeds. The blower motor should operate at all speeds. If the blower motor is inoperative, refer to «Auxiliary Blower Motor Malfunction (RPO C69 with Rear Controls)»(/chevrolet/express-g3500/2013-2013/remont/manual-hvac-system/#hvac-system-manual) , «Auxiliary Blower Motor Malfunction (RPO C36)»(/chevrolet/express-g3500/2013-2013/remont/manual-hvac-system/#hvac-system-manual) , «Auxiliary Blower Motor Malfunction (RPO C69 w/o Rear Controls)»(/chevrolet/express-g3500/2013-2013/remont/manual-hvac-system/#hvac-system-manual) .
  2. Rotate the front auxiliary HVAC control assembly air temperature control from the VENT position to the FLOOR position. The mode should follow the commanded states VENT to FLOOR. If the air temperature does not change, refer to Mode Malfunction without Rear Auxiliary Contro below.

Mode Malfunction - Front Auxiliary Control

  1. Ignition OFF, disconnect the harness connector at the front auxiliary HVAC control assembly.
  2. Ignition ON, verify a test lamp illuminates between the ignition circuit terminal J and ground. If the test lamp does not illuminate, test the ignition circuit for a short to ground or an open/high resistance.
  3. Ignition OFF, connect the harness connector at the front auxiliary HVAC control assembly. Disconnect the harness connector at the auxiliary HVAC control assembly.
  4. Ignition ON, test for ignition voltage between the signal circuit terminal E and ground. If less than the specified value, test the signal circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the front auxiliary HVAC control assembly.
  5. Ignition OFF, connect the harness connector at the auxiliary HVAC control assembly. Disconnect the harness connector at the auxiliary mode actuator.
  6. Test for less than 5 ohms between the ground circuit terminal 7 and ground. If greater than the specified range, test the ground circuit for an open/high resistance.
  7. Ignition ON, verify that a test lamp illuminates between the ignition circuit terminal 10 and ground. If the test lamp does not illuminate, test the ignition circuit for a short to ground or an open/high resistance.
  8. Install a DMM between the control circuit terminal 8 and ground. Command the actuator in each direction. Voltage on the control circuit should change from 0 volts when commanding the actuator in one direction to 12 volts in the other direction. If the voltage does not change as specified, replace the auxiliary HVAC control assembly.
  9. If all circuits test normal, test or replace the auxiliary mode actuator.

Mode Malfunction - Rear Auxiliary Control

  1. Ignition OFF, disconnect the harness connector at the rear auxiliary HVAC control assembly.
  2. Test for less than 5 ohms between the ground circuit terminal B and ground. If greater than the specified range, test the ground circuit for an open/high resistance.
  3. Ignition ON, verify a test lamp illuminates between the ignition circuit terminal G and ground. If the test lamp does not illuminate, test the ignition circuit for a short to ground or an open/high resistance.
  4. Ignition OFF, connect the harness connector at the front auxiliary HVAC control assembly. Disconnect the harness connector at the auxiliary HVAC control assembly.
  5. Ignition ON, test for ignition voltage between the signal circuit terminal D and ground. If less than the specified value, test the signal circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the rear auxiliary HVAC control assembly.
  6. If all circuits test normal, replace the auxiliary HVAC control assembly.

Mode Malfunction without Rear Auxiliary Control

  1. Ignition OFF, disconnect the harness connector at the front auxiliary HVAC control assembly.
  2. Ignition ON, verify a test lamp illuminates between the ignition circuit terminal G and ground. If the test lamp does not illuminate, test the ignition circuit for a short to ground or an open/high resistance.
  3. Ignition OFF, connect the harness connector at the front auxiliary HVAC control assembly. Disconnect the harness connector at the auxiliary mode actuator.
  4. Test for less than 5 ohms between the ground circuit terminal 7 and ground. If greater than the specified range, test the ground circuit for an open/high resistance.
  5. Ignition ON, verify that a test lamp illuminates between the ignition circuit terminal 10 and ground. If the test lamp does not illuminate, test the ignition circuit for a short to ground or an open/high resistance.
  6. Install a DMM between the control circuit terminal 8 and ground. Command the actuator in each direction. Voltage on the control circuit should change from 0 volts when commanding the actuator in one direction to 12 volts in the other direction. If the voltage does not change as specified, replace the front auxiliary HVAC control assembly.
  7. If all circuits test normal, test or replace the auxiliary mode actuator.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

  1. «Auxiliary Mode Valve Actuator Replacement»(/chevrolet/express-g3500/2013-2013/remont/manual-hvac-system/#hvac-system-manual)
  2. «Auxiliary Heater and Air Conditioning Control Replacement - Front»(/chevrolet/express-g3500/2013-2013/remont/manual-hvac-system/#hvac-system-manual)
  3. «Auxiliary Heater and Air Conditioning Control Replacement - Rear»(/chevrolet/express-g3500/2013-2013/remont/manual-hvac-system/#hvac-system-manual)
  4. «Auxiliary HVAC Control Processor Replacement»(/chevrolet/express-g3500/2013-2013/remont/manual-hvac-system/#hvac-system-manual)

Vacuum Control System Diagnostic

StepActionYesNo
DEFINITION: Improper air delivery Vacuum applied to the wrong actuator Vacuum leak
1Start the engine. Turn the blower motor fan ON and select an air outlet mode. Does air flow out of the selected HVAC outlet ducts?Go to Step 3Go to Step 2
2Did the customer concern mention that the air discharges out the correct ducts at first, but then changes during higher engine RPM?Go to Step 7Go to Step 3
3With the engine running, cycle the HVAC controls through all the modes. Does the air come out of the selected outlet ducts?Go to Step 18Go to Step 4
4With the engine running, take a vacuum reading at the manifold vacuum port that supplies vacuum to the HVAC vacuum control assembly. Is there engine vacuum?Go to Step 6Go to Step 5
5Repair the no vacuum condition. Is the repair complete?Go to Step 18
6Take a vacuum reading at the vacuum supply line at the HVAC vacuum control assembly. Is the vacuum reading the same as the engine vacuum?Go to Step 11Go to Step 8
7Disconnect the vacuum supply line from the HVAC vacuum control assembly. With the vacuum gauge connected to the vacuum supply line, re-start the engine and turn the engine OFF. Does the system lose vacuum after turning OFF the engine?Go to Step 8Go to Step 11
8Inspect for leaking or collapsed vacuum lines between the engine manifold vacuum port and the HVAC vacuum control assembly. Are the vacuum lines leaking?Go to Step 9Go to Step 10
9Repair or replace the collapsed or leaking vacuum line. Is the repair complete?Go to Step 18
10Replace the vacuum reservoir tank. Refer to Vacuum Tank Replacement . Is the repair complete?Go to Step 18
11Using an external vacuum source, apply vacuum to the appropriate vacuum line at the connector to the HVAC control assembly. Refer to Heater and Air Conditioning Control Replacement . Does the actuator retract?Go to Step 17Go to Step 12
12Inspect for leaking or collapsed vacuum lines between the actuator and the connector to the HVAC vacuum control assembly. Are the vacuum lines leaking?Go to Step 9Go to Step 13
13Disconnect the vacuum line from the actuator. Apply an external vacuum source to the actuator. Did the actuator retract?Go to Step 14Go to Step 16
14With the actuator disconnected, inspect the door for binding. Does the door move freely?Go to Step 16Go to Step 15
15Repair the binding door. Refer to the appropriate repair: Defroster Door Replacement Air Temperature Door Replacement Recirculation Door Replacement Is the repair complete?Go to Step 18
16Replace the vacuum actuator. Refer to the appropriate repair: Temperature Valve Actuator Replacement Defroster Valve Actuator Replacement Air Inlet Valve Actuator Replacement Is the repair complete?Go to Step 18
17Replace the HVAC control assembly. Refer to Heater and Air Conditioning Control Replacement . Is the repair complete?Go to Step 18
18Cycle the HVAC controls through all modes to verify proper operation. Did you correct the condition?System OKGo to Step 1

Vacuum Control System Diagnostic

Removal Procedure

  1. Remove the I/P cluster trim plate. Refer to «Instrument Panel Cluster Trim Plate Bezel Replacement»(/chevrolet/express-g3500/2013-2013/remont/exteriorinterior-trim/#instrument-panel-trim-and-console-trim) .
  2. Remove the retaining screw from the HVAC control assembly.
  3. Pivot the HVAC control assembly to disengage the locking tab on the right side.
  4. Disconnect the electrical connectors.
  5. Disconnect the vacuum connector.
  6. Remove the HVAC control assembly.

Installation Procedure

  1. Connect the vacuum connector.
  2. Connect the electrical connectors.
  3. Install the HVAC control assembly.
  4. Install the retaining screw to the HVAC control assembly and tighten to 2 N.m (18 lb in).
  5. Install the I/P cluster trim plate. Refer to «Instrument Panel Cluster Trim Plate Bezel Replacement»(/chevrolet/express-g3500/2013-2013/remont/exteriorinterior-trim/#instrument-panel-trim-and-console-trim) .

Scheme 11

Scheme 11: Heater and Air Conditioning Control Temperature Knob Replacement
Scheme 11: Heater and Air Conditioning Control Temperature Knob Replacement
CalloutComponent Name
1Heater Control Knob TIP: Remove all of the heater and air condition control temperature knobs the same way by pulling straight out.

Heater and Air Conditioning Control Temperature Knob Replacement

  1. Disconnect the air temperature actuator electrical connector.
  2. Remove the air temperature actuator retaining screws.
  3. Remove the air temperature actuator (1) from the heater assembly (2).
  1. Install the air temperature actuator (1) to the heater assembly (2).
  2. Install the air temperature actuator retaining screws and tighten to 1.9 N.m (17 lb in).
  3. Connect the air temperature actuator electrical connector.
  1. Remove the I/P upper trim pad. Refer to «Instrument Panel Upper Trim Pad Replacement»(/chevrolet/express-g3500/2013-2013/remont/exteriorinterior-trim/#instrument-panel-trim-and-console-trim) .
  2. Disconnect the vacuum hose (1) from the defrost actuator (2).
  3. Depress the clip and remove the defrost actuator (2) from the heater assembly.
  1. Install the defrost actuator (2) to the heater assembly.
  2. Connect the vacuum hose (1) to the defrost actuator (2).
  3. Install the I/P upper trim pad. Refer to «Instrument Panel Upper Trim Pad Replacement»(/chevrolet/express-g3500/2013-2013/remont/exteriorinterior-trim/#instrument-panel-trim-and-console-trim) .
  1. Rotate the instrument panel (I/P) carrier out and downward. Refer to «Instrument Panel Carrier Replacement»(/chevrolet/express-g3500/2013-2013/remont/exteriorinterior-trim/#instrument-panel-trim-and-console-trim) .
  2. Disconnect the vacuum hose from the upper mode actuator.
  3. Release the tabs from the upper mode actuator.
  4. Unhook the actuator from the upper mode door lever.
  5. Remove the upper mode actuator.
  1. Hook the upper mode door actuator to the mode door lever.
  2. Install the upper mode actuator.
  3. Press upper mode actuator on until you hear tabs engage.
  4. Connect the vacuum line to the upper mode door actuator.
  5. Reposition and install the I/P carrier. Refer to «Instrument Panel Carrier Replacement»(/chevrolet/express-g3500/2013-2013/remont/exteriorinterior-trim/#instrument-panel-trim-and-console-trim) .
  1. Remove the I/P carrier. Refer to «Instrument Panel Carrier Replacement»(/chevrolet/express-g3500/2013-2013/remont/exteriorinterior-trim/#instrument-panel-trim-and-console-trim) .
  2. Release the tabs from the lower mode actuator.
  3. Remove the lower mode actuator.
  1. Install the lower mode actuator.
  2. Press lower mode actuator on until you hear tabs engage.
  3. Install the I/P carrier. Refer to «Instrument Panel Carrier Replacement»(/chevrolet/express-g3500/2013-2013/remont/exteriorinterior-trim/#instrument-panel-trim-and-console-trim) .

Special Tools

J 39400-A Electronic Halogen Leak Detector

  1. Remove the battery. Refer to «Battery Replacement (Primary)»(/chevrolet/express-g3500/2013-2013/remont/charging-system/#battery-charging-system-and-starting-system) .
  2. Recover the refrigerant from the A/C system. Refer to «Refrigerant Recovery and Recharging»(/chevrolet/express-g3500/2013-2013/remont/manual-hvac-system/#heating-ventilation-and-air-conditioning) .
  3. Disconnect the low pressure sensor electrical connector.
  4. Disconnect the blower motor electrical connector.
  5. Disconnect the blower motor resistor assembly electrical connector.
  6. Remove the evaporator outlet hose retaining nuts (4, 5).
  7. Remove the retaining nut (3) from the evaporator inlet tube (5).
  8. Remove the evaporator inlet tube from the evaporator and position aside.
  9. Remove the sealing washers.
  10. Remove the fourteen screws (1) from the evaporator and blower module assembly case.
  11. Reposition the accumulator aside.
  12. Remove the evaporator and blower module assembly front cover (2) from the evaporator case (3).
  13. Grasp recirculation door seal and open (1) to gain access to actuator mounting.
  14. Release actuator mounting tab (2) and slide rearward.
  15. Rotate actuator 90° clockwise (rearward) to release door linkage (3).
  16. Remove actuator vacuum line (4).
  17. Remove recirculation actuator (5).
  1. Install the recirculation door actuator (5) to the linkage (3).
  2. Install the actuator into mounting position (2) and attach vacuum line (4). NOTE: Ensure the recirculation door (1) operates without binding and seals properly.
  3. Reposition the accumulator for installation.
  4. Install the evaporator and blower module assembly cover (2) to evaporator case (3).
  5. Secure cover with the fourteen screws (1) and tighten to 1.9 N.m (17 lb in).
  6. Install new sealing washers to the evaporator inlet and outlet tubes. Refer to «Air Conditioning System Seal Replacement»(/chevrolet/express-g3500/2013-2013/remont/manual-hvac-system/#heating-ventilation-and-air-conditioning) .
  7. Install the evaporator inlet tube (4) to the evaporator (5).
  8. Install the evaporator inlet tube retaining nut (3) and tighten to 16 N.m (12 lb ft).
  9. Install the evaporator outlet hose and retaining nuts (4, 5) and tighten to 18 N.m (13 lb ft).
  10. Connect the low pressure sensor electrical connector.
  11. Connect the blower motor electrical connector.
  12. Connect the blower motor resistor assembly electrical connector.
  13. Evacuate and recharge the A/C system. Refer to «Refrigerant Recovery and Recharging»(/chevrolet/express-g3500/2013-2013/remont/manual-hvac-system/#heating-ventilation-and-air-conditioning) .
  14. Leak test the fittings of the repaired or replaced component using the J 39400-A Electronic Halogen Leak Detector.
  15. Install the battery. Refer to «Battery Replacement (Primary)»(/chevrolet/express-g3500/2013-2013/remont/charging-system/#battery-charging-system-and-starting-system) .
  1. Remove the primary battery tray. Refer to «Battery Tray Replacement (Primary)»(/chevrolet/express-g3500/2013-2013/remont/charging-system/#battery-charging-system-and-starting-system) .
  2. Disconnect the vacuum hose from the vacuum tank.
  3. Remove the screws (1) from the vacuum tank retainers.
  4. Remove the vacuum tank (3) from the battery tray.
  1. Install the vacuum tank (3).
  2. Install the screws (1) to the vacuum tank retainers and tighten to 6 N.m (53 lb in).
  3. Connect the vacuum hose.
  4. Install the primary battery tray. Refer to «Battery Tray Replacement (Primary)»(/chevrolet/express-g3500/2013-2013/remont/charging-system/#battery-charging-system-and-starting-system) .

Scheme 12

Scheme 12: Vacuum Pump Assembly Replacement
Scheme 12: Vacuum Pump Assembly Replacement
CalloutComponent Name
Preliminary Procedure Remove the primary battery tray. Refer to Battery Replacement (Primary) .
1Rubber Retainers (Qty: 3)
2Vacuum Pump Assemby

Vacuum Pump Assembly Replacement

  1. Remove the front control switch bezel (4) from the headliner.
  2. Remove the front control switch (3) by unsnapping the retainers from the headliner.
  3. Disconnect the electrical connector.
  1. Connect the electrical connector.
  2. Install the front control switch (3) by snapping the retainers to the headliner.
  3. Install the front control switch bezel (4) to the headliner.
  1. Remove the HVAC control assembly bezel (3) from the headliner (2).
  2. Lower the front headliner to access the rear of the HVAC control assembly (1). Refer to «Headlining Front Trim Panel Replacement»(/chevrolet/express-g3500/2013-2013/remont/exteriorinterior-trim/#floor-coverings-and-headlinings) .
  3. Disconnect the electrical connectors.
  4. Remove the HVAC control assembly from the front headliner.
  1. Install the HVAC control assembly (1) in the front headliner and attach the bezel (3).
  2. Connect the electrical connectors.
  3. Install the front headliner (2). Refer to «Headlining Front Trim Panel Replacement»(/chevrolet/express-g3500/2013-2013/remont/exteriorinterior-trim/#floor-coverings-and-headlinings) .
  1. Lower the front headliner to access the HVAC control processor. Refer to «Headlining Front Trim Panel Replacement»(/chevrolet/express-g3500/2013-2013/remont/exteriorinterior-trim/#floor-coverings-and-headlinings) .
  2. Remove the HVAC control processor from the roof panel.
  3. Remove the HVAC control processor access cover (3).
  4. Remove the HVAC control processor (2) from the HVAC processor case (1).
  1. Install the HVAC control processor (2) to the HVAC processor case (1).
  2. Install the HVAC control processor access cover (3).
  3. Install the HVAC control processor to the roof panel.
  4. Install the front headliner. Refer to «Headlining Front Trim Panel Replacement»(/chevrolet/express-g3500/2013-2013/remont/exteriorinterior-trim/#floor-coverings-and-headlinings) .

Scheme 13

Scheme 13: Auxiliary Blower Switch Replacement
Scheme 13: Auxiliary Blower Switch Replacement
CalloutComponent Name
1Instrument Panel Cluster Trim Plate Bezel Assembly Refer to Instrument Panel Cluster Trim Plate Bezel Replacement .
2Auxiliary Blower Motor Switch Assembly Procedure Squeeze the retaining tabs on the back of the switch and push the switch out of the cluster trim bezel assembly.

Auxiliary Blower Switch Replacement

  1. Remove the left rear quarter trim panel. Refer to «Body Side Trim Panel Replacement - Left Side»(/chevrolet/express-g3500/2013-2013/remont/exteriorinterior-trim/#interior-trim-and-interior-paneling) .
  2. Disconnect the electrical connector from the air temperature actuator.
  3. Remove the retaining screws from the air temperature actuator.
  4. Remove the air temperature actuator.
  1. Install the air temperature actuator.
  2. Install the retaining screws to the air temperature actuator and tighten to 1.9 N.m (17 lb in).
  3. Connect the air temperature electrical connector to the actuator.
  4. Install the left rear quarter trim panel. Refer to «Body Side Trim Panel Replacement - Left Side»(/chevrolet/express-g3500/2013-2013/remont/exteriorinterior-trim/#interior-trim-and-interior-paneling) .
  1. Remove the auxiliary HVAC module assembly. Refer to «Auxiliary HVAC Module Removal and Installation»(/chevrolet/express-g3500/2013-2013/remont/manual-hvac-system/#heating-ventilation-and-air-conditioning) .
  2. Remove the retaining screws from the auxiliary mode actuator.
  3. Remove the auxiliary mode actuator.
  1. Install the auxiliary mode actuator.
  2. Install the retaining screws to the auxiliary mode actuator and tighten to 1.9 N.m (17 lb in).
  3. Install the auxiliary HVAC module assembly. Refer to «Auxiliary HVAC Module Removal and Installation»(/chevrolet/express-g3500/2013-2013/remont/manual-hvac-system/#heating-ventilation-and-air-conditioning) .

Air Delivery Description and Operation

The air delivery description and operation is divided into 6 areas

  1. HVAC Control Components
  2. Air Speed
  3. Auxiliary Air Speed
  4. Air Distribution
  5. Auxiliary Air Delivery
  6. Recirculation Operation

HVAC Control Components

HVAC Control Assembly

The HVAC control assembly is a non-class 2 device that interfaces between the operator and the HVAC system to maintain air temperature and distribution settings. The ignition 3 voltage circuit provides power to the control assembly. Two integrated potentiometers control air temperature door position and blower motor speed. The integrated vacuum system controls the mode door position. The control assembly supports the following features

FeatureAvailability
AfterblowNo
PurgeNo
PersonalizationNo
Actuator CalibrationNo

Auxiliary HVAC Control Processor

The auxiliary HVAC control processor controls all outputs for the auxiliary HVAC system. The auxiliary HVAC control processor receives inputs from the front and rear auxiliary HVAC control assemblies. The auxiliary HVAC control processor does not utilize Class 2 communications. If the auxiliary HVAC control processor receives a 12 volt varied voltage input for an auxiliary air temperature actuator change request. Then the auxiliary HVAC control processor creates a 12 volt varied output for control of the auxiliary air temperature actuator.

Auxiliary Mode Actuator

The auxiliary mode actuator is a 3 wire bi-directional electric motor. Ignition 3 voltage, ground and control circuits enable the actuator to operate. The control circuit uses a 0-12 volt linear-ramped signal to command the actuator movement. The 0 and 12 volt control values represent the opposite limits of the actuator range of motion. The values in between 0 and 12 volts correspond to the positions between the limits. When the HVAC control assembly sets a commanded, or targeted, value, the control signal is set to a value between 0-12 volts. The actuator shaft rotates until the commanded position is reached. The module will maintain the control value until a new commanded value is needed.

Air Speed

The HVAC control assembly applies voltage to the blower motor control circuit that corresponds to the selected blower speed. The resistors and the blower motor are in a series circuit. The following list represents the number of resistors in series with the blower motor per particular speed request

  1. Low speed-3 resistors
  2. Medium 1 speed-2 resistors
  3. Medium 2 speed-1 resistor

When the operator requests High speed, the HVAC control assembly applies voltage to the blower motor relay through the high blower motor control circuit. The voltage energizes the blower motor relay, connecting the blower motor to battery positive voltage.

Auxiliary Air Speed

The auxiliary HVAC control assembly applies voltage to the auxiliary blower motor control circuit that corresponds to the selected blower speed. The resistors and the blower motor are in a series circuit. The following list represents the number of resistors in series with the blower motor per particular speed request

  1. Low speed-2 resistors
  2. Medium speed-1 resistor

When the operator requests High speed, the HVAC control assembly applies voltage to the blower motor relay through the auxiliary high blower motor control circuit. The voltage energizes the blower motor relay, connecting the blower motor to battery positive voltage.

Air Distribution

Vacuum Pump

The electric vacuum pump supplies vacuum to the HVAC module. When the ignition is ON, voltage is supplied to the vacuum pump from the HVAC fuse. The ground is supplied to the vacuum pump from the chassis. When the ignition is ON, the HVAC doors function properly.

Mode Switch

The mode switch is a rotary vacuum valve that directly applies vacuum to the appropriate vacuum actuator. Use the mode switch to change the air delivery mode in the vehicle.

MAX A/C-If Equipped

When the operator selects MAX A/C, the mode actuator has vacuum applied to it through the Brown vacuum line, making the vent door open. The recirculation actuator has vacuum applied to it through the Orange vacuum line, making the recirculation door close and allowing air to be recirculated. A/C is forced ON.

A/C-If Equipped

When the operator selects A/C, the mode actuator has vacuum applied to it through the Brown vacuum line, making the vent door open. A/C is forced ON.

Bi-Level Mode

When the operator selects Bi-Level, the following occurs

  1. The mode actuator is in neutral position.
  2. The defrost actuator has vacuum applied to it through the Yellow vacuum line.
  3. The defrost actuator closes the defrost door, thus opening the heater door though mechanical linkage.
  4. Vacuum is bled off the mode actuator and the vent door is held stationary in the half open position.

Vent Mode

When the operator selects VENT, the mode actuator has vacuum applied to it through the Yellow vacuum line, making the vent door open.

Floor Mode

When the operator selects FLOOR, the defrost actuator has vacuum applied to it through the Pink vacuum line, pulling the defrost door closed and opening the heater door through mechanical linkage.

Mix-Blend Mode

When the operator selects Mix-Blend, the following occurs

  1. Vacuum is bled off the defrost actuator, holding the defrost door stationary in the half-open position. The heater door is also held stationary in the half-open position through mechanical linkage.
  2. A/C is forced ON.
  3. Recirculation is not available.

Defrost Mode

When the operator selects Defrost, the following occurs

  1. The defrost actuator has vacuum applied to it through the Blue vacuum line, pushing the defrost door open and closing the heater door through mechanical linkage.
  2. A/C is forced ON.
  3. Recirculation is not available.

Auxiliary Air Distribution

The HVAC control assembly controls the mode actuator in order to distribute airflow to a desired outlet. When the mode door is moved to the defrost position, the A/C compressor clutch engages and the recirculation actuator will be moved to the outside air position. Regardless of the mode setting, a small amount of air will be diverted to the defrost ducts to reduce windshield fogging. When VENT is selected, the following will occur

  1. The mode actuator will be moved to the panel position.
  2. The recirculation actuator will be placed in the outside air position.
  3. The A/C compressor will be commanded off.

Recirculation Operation

When the operator selects Recirculation, the HVAC control assembly connects the recirculation door vacuum actuator to the vacuum source. The recirculation actuator retracts, closing the recirculation door. The recirculation operation can function with blower motor in either the ON or OFF position. Recirculation will continue until either outside air is selected or the next ignition cycle. Recirculation is not available in Defrost and Mix-Blend mode.

Air Temperature Description and Operation

The air temperature controls are divided into five areas.

  1. HVAC Control Components
  2. Heating and A/C Operation
  3. Auxiliary Heating and A/C Operation
  4. Engine Coolant
  5. A/C Cycle

HVAC Control Assembly

The HVAC control assembly is a non-class 2 device that interfaces between the operator and the HVAC system to maintain air temperature and distribution settings. The ignition 3 voltage circuits provide power to the control assembly. Two integrated potentiometers control air temperature door position and blower motor speed. The integrated vacuum system controls the mode door position. The control assembly supports the following features

FeatureAvailability
AfterblowNo
PurgeNo
PersonalizationNo
Actuator CalibrationNo

Auxiliary HVAC Control Processor

The auxiliary HVAC control processor controls all outputs for the auxiliary HVAC system. The auxiliary HVAC control processor receives inputs from the front and rear auxiliary HVAC control assemblies. The auxiliary HVAC control processor does not utilize Class 2 communications.

If the auxiliary HVAC control processor receives a 12-volt varied voltage input for an auxiliary air temperature actuator change request. Then the auxiliary HVAC control processor creates a 12-volt varied output for control of the auxiliary air temperature actuator.

Air Temperature Actuator

The air temperature actuator and auxiliary air temperature actuator are a 3-wire bi-directional electric motor. Ignition 3 voltage, ground and control circuits enable the actuator to operate. The control circuit uses a 0-12-volt linear-ramped signal to command the actuator movement. The 0 and 12-volt control values represent the opposite limits of the actuator range of motion. The values in between 0 and 12 volts correspond to the positions between the limits.

When the HVAC control assembly sets a commanded, or targeted, value, the control signal is set to a value between 0-12 volts. The actuator shaft rotates until the commanded position is reached. The module will maintain the control value until a new commanded value is needed.

A/C Pressure Switches

The A/C system is protected by two A/C pressure switches.

  1. A/C low pressure switch
  2. A/C high pressure switch

The A/C high pressure switch interrupts the A/C request signal when the A/C line pressure is more than a predetermined value. The A/C low pressure switch interrupts the A/C low pressure switch signal when the A/C line pressure is less than or more than a predetermined value. When the powertrain control module (PCM) stops receiving the required signals, the A/C compressor clutch relay control circuit is no longer grounded, disengaging the A/C compressor clutch. The A/C compressor clutch is disengaged under the following conditions

  1. A/C low pressure switch is less than 124 kPa (18 psi).
  2. A/C low pressure switch is more than 338 kPa (49 psi).
  3. A/C high pressure switch is more than 2896 kPa (420 psi).

Bypass Valves

The bypass valves included in the air temperature system are

  1. Coolant Bypass Valve
  2. Hot Water Bypass Valve

The bypass valve is a normally open valve, which closes when vacuum is applied to the valve. When the MAX A/C mode is selected, vacuum from the HVAC control assembly is applied to the bypass valve. The vacuum must be strong enough to overcome the tension of the valve's internal return spring in order to close the bypass valve. The return spring forces the valve to return to the open position, when any of the other HVAC modes are selected. In the closed position, the flow of coolant to the heater core is bypassed, allowing maximum cooling to the passenger compartment.

Heating and A/C Operation

The purpose of the heating and A/C system is to provide heated and cooled air to the interior of the vehicle. The A/C system will also remove humidity from the interior and reduce windshield fogging. The vehicle operator can determine the passenger compartment temperature by adjusting the air temperature switch. Regardless of the temperature setting, the following can effect the rate that the HVAC system can achieve the desired temperature

  1. Recirculation
  2. Difference between inside and desired temperature
  3. Difference between ambient and desired temperature
  4. Blower motor speed setting
  5. Mode setting
  6. Auxiliary HVAC settings

The A/C system can be engaged by placing the mode switch in one of the following positions

  1. Max A/C
  2. A/C
  3. Bi-Level
  4. Blend
  5. Defrost

The A/C system can operate regardless of the temperature setting. Regardless of the selected A/C mode setting, a request is sent to the PCM to turn on the A/C compressor clutch.

The following conditions must be met in order for the PCM to turn on the compressor clutch

  1. Ambient air temperature is greater than 3°C (38°F)
  2. Engine coolant temperature (ECT) is less than 123°C (253°F)
  3. Engine speed is less than 5000 RPM
  4. The A/C compressor cycling switch pressure is between 124-388 kPa (18-49 psi)
  5. The A/C high pressure cutout switch is less than 2896 kPa (420 psi)

Once engaged, the compressor clutch will be disengaged for the following conditions

  1. Throttle position is 100 percent
  2. The A/C compressor cycling switch pressure is less than 124 kPa (18 psi) or more than 338 kPa (49 psi)
  3. The A/C high pressure cutout switch is more than 2896 kPa (420 psi)
  4. Engine coolant temperature (ECT) is more than 123°C (253°F)
  5. Engine speed is more than 5000 RPM
  6. Transmission shift
  7. PCM detects excessive torque load
  8. PCM detects insufficient idle quality
  9. PCM detects a hard launch condition

When the compressor clutch disengages, the compressor clutch diode protects the electrical system from a voltage spike.

Heater Mode - Auxiliary Heater without A/C

The auxiliary blower motor recycles air from the vehicle's interior. The vehicle operator can determine the intensity of the auxiliary heater by placing the auxiliary blower motor in one of the following positions

  1. Low
  2. Med
  3. High

Since there is no temperature switch, the temperature is controlled by the speed of the auxiliary blower motor. The auxiliary blower motor will only operate when the ignition is in the RUN position, and the auxiliary blower motor switch is in any position other than OFF.

Heater Mode - Front Auxiliary HVAC Control Assembly Only

The auxiliary temperature switch in the front auxiliary HVAC control assembly allows the vehicle operator to adjust the temperature in the rear of the vehicle. Power is provided to both the front auxiliary HVAC control assembly and the auxiliary air temperature actuator from the instrument panel (I/P) fuse block on the ignition 3 voltage circuit.

Voltage delivered to the front auxiliary HVAC control assembly on the ignition 3 voltage circuit is sent to a variable resistor. Based on the placement of the temperature switch, a varied voltage is sent to the auxiliary air temperature actuator on the auxiliary air temperature door control circuit. The auxiliary air temperature actuator positions the temperature door to divert the appropriate amount of air past the heater core in order to achieve the desired temperature.

Heater Mode - Front Auxiliary HVAC Control Assembly with Rear Auxiliary HVAC Control Assembly

The auxiliary temperature switch in the front auxiliary HVAC control assembly allows the vehicle operator to adjust the temperature in the rear of the vehicle. Power is provided to both the front auxiliary HVAC control assembly and the auxiliary air temperature actuator from the (I/P) fuse block on the ignition 3 voltage circuit.

Voltage delivered to the front auxiliary HVAC control assembly on the ignition 3 voltage circuit is sent to a varied resistor. Based on the placement of the temperature switch, a varied voltage is sent to the auxiliary air temperature actuator on the auxiliary air temperature door control circuit, and auxiliary HVAC control processor. The auxiliary air temperature actuator positions the temperature door to divert the appropriate amount of air past the heater core in order to achieve the desired temperature

Heater Mode - Rear Auxiliary HVAC Control Assembly

The auxiliary temperature switch in the rear auxiliary HVAC control assembly allows the rear seat passengers to adjust the temperature in the rear of the vehicle. Power is provided to the rear auxiliary HVAC control assembly, auxiliary HVAC control processor and the auxiliary air temperature actuator from the (I/P) fuse block on the ignition 3 voltage circuit.

To activate the rear auxiliary HVAC control assembly, the front auxiliary HVAC control assembly must be placed in the REAR CNTL position. Ignition 3 voltage is sent to the auxiliary HVAC control processor. When the switch is placed in the REAR CNTL position, the voltage is grounded through the auxiliary blower motor switch control, front auxiliary HVAC control assembly and the ground circuit to allow the rear auxiliary HVAC control assembly to operate the auxiliary temperature actuator. Voltage delivered to the rear auxiliary HVAC control assembly on the ignition 3 voltage circuit is sent to a variable resistor. Based on the placement of the temperature switch, a varied voltage is sent to the auxiliary air temperature actuator on the auxiliary air temperature door control circuit, and auxiliary HVAC control processor. The auxiliary air temperature actuator positions the temperature door to divert the appropriate amount of air past the heater core in order to achieve the desired temperature.

A/C Mode - Front Auxiliary HVAC Control Assembly Only

The auxiliary temperature switch in the front auxiliary HVAC control assembly allows the vehicle operator to adjust the temperature in the rear of the vehicle. Power is provided to both the front auxiliary HVAC control assembly and the auxiliary air temperature actuator from the (I/P) fuse block on the ignition 3 voltage circuit.

Voltage delivered to the front auxiliary HVAC control assembly on the ignition 3 voltage circuit is sent to a variable resistor. Based on the placement of the temperature switch, a varied voltage is sent to the auxiliary air temperature actuator on the auxiliary air temperature door control circuit. The auxiliary air temperature actuator positions the temperature door to divert the appropriate amount of air past the heater core in order to achieve the desired temperature.

A/C Mode - Front Auxiliary HVAC Control Assembly with Rear Auxiliary HVAC Control Assembly

The auxiliary temperature switch in the front auxiliary HVAC control assembly allows the vehicle operator to adjust the temperature in the rear of the vehicle. Power is provided to both the front auxiliary HVAC control assembly and the auxiliary air temperature actuator from the (I/P) fuse block on the ignition 3 voltage circuit.

Voltage delivered to the front auxiliary HVAC control assembly on the ignition 3 voltage circuit is sent to a variable resistor. Based on the placement of the temperature switch, a varied voltage is sent to the auxiliary air temperature actuator on the auxiliary air temperature door control circuit, and auxiliary HVAC control processor. The auxiliary air temperature actuator positions the temperature door to divert the appropriate amount of air past the heater core in order to achieve the desired temperature.

A/C Mode - Rear Auxiliary HVAC Control Assembly

The auxiliary temperature switch in the rear auxiliary HVAC control assembly allows the rear seat passengers to adjust the temperature in the rear of the vehicle. Power is provided to the rear auxiliary HVAC control assembly, auxiliary HVAC control processor and the auxiliary air temperature actuator from the (I/P) fuse block on the ignition 3 voltage circuit.

To activate the rear auxiliary HVAC control assembly, the front auxiliary HVAC control assembly must be placed in the REAR CNTL position. Ignition 3 voltage is sent to the auxiliary HVAC control processor. When the switch is placed in the REAR CNTL position, the voltage is grounded through the auxiliary blower motor switch control, front auxiliary HVAC control assembly and the ground circuit to allow the rear auxiliary HVAC control assembly to operate the auxiliary temperature actuator. Voltage delivered to the rear auxiliary HVAC control assembly on the ignition 3 voltage circuit is sent to a varied resistor. Based on the placement of the temperature switch, a varied voltage is sent to the auxiliary air temperature actuator on the auxiliary air temperature door control circuit, and auxiliary HVAC control processor. The auxiliary air temperature actuator positions the temperature door to divert the appropriate amount of air past the heater core in order to achieve the desired temperature.

Engine Coolant

Engine coolant is the key element of the heating system. The thermostat controls engine operating coolant temperature. The thermostat also creates a restriction for the cooling system that promotes a positive coolant flow and helps prevent cavitation. Coolant enters the heater core through the inlet heater hose, in a pressurized state.

The heater core is located inside the HVAC module. The heat of the coolant flowing through the heater core is absorbed by the ambient air drawn through the HVAC module. Heated air is distributed to the passenger compartment, through the HVAC module, for passenger comfort.

The amount of heat delivered to the passenger compartment is controlled by opening or closing the HVAC module air temperature door. The coolant exits the heater core through the return heater hose and recirculated back through the engine cooling system.

Coolant Heater (K08)

The coolant heater function is to provide additional heat to the passenger compartment. The coolant heater burns diesel fuel, to heat up the engine coolant when the vehicle is running and will only operate during conditions where ambient temperature is below 4°C (39°F) and a fuel tank level greater than 12.5 percent. The heat of the hot engine coolant is transferred to the HVAC module to heat the passenger compartment. The coolant heater does not heat up instantly. It must go through a self test and start up procedure before normal operation. The vehicle must be running to start the unit but after the unit is no longer commanded on a two minute shut down (purge) procedure starts. The coolant flow is from the engine to the fuel operated heater through the heat exchanger back to the engine.

Battery voltage and ground is supplied to the coolant heater. The electronic control unit inside the coolant heater determines when the unit will turn ON and OFF as well as how it will function. The electronic control unit also uses GMLAN communication and the engine control module (ECM) to transfer coolant heater information that the scan tool can read. The fuel operated heater contains flame sensors to disable the glow plug once the flame is established or to abort the startup attempt if the flame is not established.

Inputs to the coolant heater electronic control unit

  1. Coolant sensor
  2. Overheat sensor
  3. Combustion sensor
  4. GMLAN ECM

Outputs from the coolant heater electronic control unit

  1. Fuel pump
  2. Glow plug
  3. Blower motor
  4. GMLAN ECM

The coolant heater controls the coolant temperature with 3 operating modes.

  1. HIGH-If coolant temperature is in a range between -40 to +75°C (-40 to +176°F), the coolant heater fuel pump will pump fuel at maximum capacity to increase the coolant temperature as fast as possible. Note: Ambient temperature must be below 4°C (39°F), fuel tank level greater than 12.5 percent and the engine should be running.
  2. LOW-If coolant temperature is in a range between 85-90°C (185-194°F), the coolant heater fuel pump will pump fuel at minimum capacity to increase the coolant temperature at a slower rate.
  3. OFF-If coolant temperature is above 90°C (195°F), the coolant heater fuel pump will stop pumping fuel and allow the remaining fuel in the combustion chamber to burn out. The coolant heater fuel pump will not start pumping fuel again until the coolant temperature reaches 75°C (167°F).

FUNCTIONAL PRINCIPLES

  1. The vehicle coolant pump continuously circulates the coolant over the heat exchanger inside the fuel operated heater and throughout the coolant system.
  2. The coolant heater fuel pump pumps the fuel from the vehicle fuel tank to the combustion chamber.
  3. Coolant heater blower blows the oxygen, which is necessary for the combustion process, into the combustion chamber.
  4. A Coolant heater glow plug generates the evaporation energy and creates the temperature which is necessary to ignite the Air-Fuel mixture
  5. The heat exchanger inside the fuel operated heater transfers the energy of the combustion process into the engine coolant.
  6. Depending on the coolant temperature, which is detected by the coolant sensors, the heater chooses either high or low setting or gets shut off.

SELF TEST OF THE UNIT

Before every start of the heater, the operation of the individual components is tested.

  1. Fuel operated heater control unit check
  2. Flame sensor
  3. Coolant sensor
  4. Overheating sensor
  5. Glow plug
  6. Fuel pump
  7. Blower motor

The fuel operated heater will only start after the self test of the heating unit is successful. Should a fault be detected, a fault notification will be output through the vehicle diagnosis.

DESCRIPTION OF SAFETY MECHANISM

During start up the ECU is performing a random access memory (RAM), read-only memory (ROM) and electrically erasable programmable read-only memory (EEPROM) test. If failures occur during a self test of the unit, the unit will not start.

  1. If the power supply voltage exceeds 16 volts the unit will not start or shut off with after purge time of 120 seconds.
  2. If the power supply voltage goes below 10.2 V for more than 40 seconds the unit will shut off and try to restart after a purge time of 120 seconds. If the failure occurs 3 times, then unit is not going to restart till next key off.

Description of component checks

  1. Coolant Heater Blower Motor-After the unit is commanded on and before normal operation the blower is tested for an open circuit. While the heater is activated the blower is tested for a short to ground.
  2. Flame sensor-The flame sensor is tested continuously during operation for a short to ground, short to voltage or open circuit.
  3. Glow plug-After the unit is commanded and before normal operation the glow plug is tested for an open circuit. While the heater is activated the glow plug is tested for a short to ground.
  4. Coolant Heater Fuel Pump-After the coolant heater is commanded on and before normal operation is activated, the fuel pump is tested for an open circuit. While the coolant heater is activated the fuel pump is tested for a short to ground.
  5. Overheating Sensor and Coolant sensor-The overheat sensor and coolant sensor are tested continuously during operation for a short to ground, short to voltage or open circuit.

FIRST START OF THE UNIT (125 seconds)

After the self test was successfully completed a first start procedure sequence is attempted.

  1. The ceramic glow plug starts to heat the combustion chamber.
  2. After a delay, the blower switches on. During the start procedure, the blower continuously increases blowing speed.
  3. The fuel pump pumps fuel into the combustion chamber. The cycle frequency of the fuel pump is also continuously increased during the start procedure.
  4. The glow plug starts to vaporize the fuel, and creates the temperature to ignite the fuel.
  5. After ignition, the heater runs continuously to reach the maximum heating power.
  6. After the flame sensor has detected the flame, the start procedure is complete, and the glow plug switches off.

SECOND START OF THE UNIT (125 seconds)

If the first start is not successful, the heater attempts a second restart process. In doing this, the glow plug voltage is increased, in order to obtain better starting conditions. The first start sequence is then repeated.

UNSUCCESSFUL SECOND START

If the second start is not successful in igniting the heater, a fault code is output from the heater.

  1. A new attempt to start will only occur after the ignition switch is cycled.
  2. After 10 failed ignition cycles one after the other, all further start attempts are stopped by the control unit. This inhibit state can only be released by clearing the codes with a scan tool.

A/C Cycle

Refrigerant is the key element in an air conditioning system. R-134a is presently the only EPA approved refrigerant for automotive use. R-134a is an very low temperature gas that can transfer the undesirable heat and moisture from the passenger compartment to the outside air.

The A/C compressor is belt driven and operates when the magnetic clutch is engaged. The compressor builds pressure on the vapor refrigerant. Compressing the refrigerant also adds heat to the refrigerant. The refrigerant is discharged from the compressor, through the discharge hose, and forced to flow to the condenser and then through the balance of the A/C system. The A/C system is mechanically protected with the use of a high pressure relief valve. If the high pressure switch were to fail or if the refrigerant system becomes restricted and refrigerant pressure continued to rise, the high pressure relief will pop open and release refrigerant from the system.

Compressed refrigerant enters the condenser in a high temperature, high pressure vapor state. As the refrigerant flows through the condenser, the heat of the refrigerant is transferred to the ambient air passing through the condenser. Cooling the refrigerant causes the refrigerant to condense and change from a vapor to a liquid state.

The condenser is located in front of the radiator for maximum heat transfer. The condenser is made of aluminum tubing and aluminum cooling fins, which allows rapid heat transfer for the refrigerant. The semi-cooled liquid refrigerant exits the condenser and flows through the liquid line, to the orifice tube.

The orifice tube is located in the liquid line between the condenser and the evaporator. The orifice tube is the dividing point for the high and the low pressure sides of the A/C system. As the refrigerant passes through the orifice tube, the pressure on the refrigerant is lowered. Due to the pressure differential on the liquid refrigerant, the refrigerant will begin to vaporize at the orifice tube. The orifice tube also meters the amount of liquid refrigerant that can flow into the evaporator.

Refrigerant exiting the orifice tube flows into the evaporator core in a low pressure, liquid state. Ambient air is drawn through the HVAC module and passes through the evaporator core. Warm and moist air will cause the liquid refrigerant boil inside of the evaporator core. The boiling refrigerant absorbs heat from the ambient air and draws moisture onto the evaporator. The refrigerant exits the evaporator through the suction line and back to the compressor, in a vapor state, and completing the A/C cycle of heat removal. At the compressor, the refrigerant is compressed again and the cycle of heat removal is repeated.

The conditioned air is distributed through the HVAC module for passenger comfort. The heat and moisture removed from the passenger compartment will also change form, or condense, and is discharged from the HVAC module as water.

A/C Cycle with Auxiliary

The auxiliary A/C system operates from the vehicles primary A/C system. The front or primary A/C system must be ON to allow the rear A/C system to function.

Refrigerant is the key element in an air conditioning system. R-134a is presently the only EPA approved refrigerant for automotive use. R-134a is an very low temperature gas that can transfer the undesirable heat and moisture from the passenger compartment to the outside air.

The A/C system used on this vehicle is a non cycling system. Non cycling A/C systems use a high pressure switch to protect the A/C system from excessive pressure. The high pressure switch will OPEN the electrical signal, to the compressor clutch, in the event that the refrigerant pressure becomes excessive. After the high and low side of the A/C system pressure equalize, the high pressure switch will CLOSE. Closing the high pressure switch will complete the electrical circuit to the compressor clutch. The A/C system is also mechanically protected with the use of a high pressure relief valve. If the high pressure switch were to fail or if the refrigerant system becomes restricted and refrigerant pressure continued to rise, the high pressure relief will pop open and release refrigerant from the system.

The A/C compressor is belt driven and operates when the magnetic clutch is engaged. The compressor builds pressure on the vapor refrigerant. Compressing the refrigerant also adds heat to the refrigerant. The refrigerant is discharged from the compressor, through the discharge hose, and forced to flow to the condenser and then through the balance of the A/C system.

Compressed refrigerant enters the condenser in a high temperature, high pressure vapor state. As the refrigerant flows through the condenser, the heat of the refrigerant is transferred to the ambient air passing through the condenser. Cooling the refrigerant causes the refrigerant to condense and change from a vapor to a liquid state.

The condenser is located in front of the radiator for maximum heat transfer. The condenser is made of aluminum tubing and aluminum cooling fins, which allows rapid heat transfer for the refrigerant. The semi-cooled liquid refrigerant exits the condenser and flows through the liquid line. The liquid line flow is split and the liquid refrigerant flows to both the front or primary A/C system, and to the liquid line for the rear A/C system.

The liquid refrigerant, flowing to the rear A/C system, flows into the rear TXV. The rear TXV is located at the rear evaporator inlet. The TXV is the dividing point for the high and the low pressure sides of the rear A/C system. As the refrigerant passes through the TXV, the pressure on the refrigerant is lowered. Due to the pressure differential on the liquid refrigerant, the refrigerant will begin to boil at the expansion device. The TXV also meters the amount of liquid refrigerant that can flow into the evaporator.

Refrigerant exiting the TXV flows into the evaporator core in a low pressure, liquid state. Ambient air is drawn through the rear A/C module and passes through the evaporator core. Warm and moist air will cause the liquid refrigerant boil inside of the evaporator core. The boiling refrigerant absorbs heat from the ambient air and draws moisture onto the evaporator. The refrigerant exits the evaporator through the suction line and back to the primary A/C systems suction line. Refrigerant in the primary A/C system suction line flows back to the compressor, in a vapor state, and completes the A/C cycle of heat removal. At the compressor, the refrigerant is compressed again and the cycle of heat removal is repeated.

The conditioned air is distributed through the rear A/C module for passenger comfort. The heat and moisture removed from the rear passenger compartment will also change form, or condense, and is discharged from the rear A/C module as water.

See also:
• Diagnostic System Check - Vehicle
• Strategy Based Diagnosis
• Diagnostic Procedure Instructions
• COMPONENT CONNECTOR END VIEWS - INDEX
• Circuit Testing
• Connector Repairs
• Testing for Intermittent Conditions and Poor Connections
• Wiring Repairs
• Control Module References
• Diagnostic Repair Verification
• Heater Coolant Heater Glow Plug Replacement
• Relay Replacement (Within an Electrical Center)
• Checking Aftermarket Accessories
• Defrosting Insufficient
• Noise Diagnosis - Blower Motor
• Noise Diagnosis - Air Conditioning (A/C) System
• Noise Diagnosis - HVAC Module
• Odor Diagnosis
• Instrument Panel Cluster Trim Plate Bezel Replacement
• Fastener Caution
• Battery Replacement (Primary)
• Headlining Front Trim Panel Replacement
• Body Side Trim Panel Replacement - Left Side
• DTC B0440, B0441, or B0442
• Air Temperature Description and Operation
• Air Delivery Description and Operation
• Vacuum Control System Diagnostic

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