HVAC System - Automatic GMC Sierra 2500

Fastener Tightening Specifications

Fastener Tightening Specifications

Sensor Resistance Table

Sensor Resistance Table

Scheme 40

Scheme 41

Scheme 42

Scheme 43

Scheme 44

Scheme 45

Diagnostic Code Index

DIAGNOSTIC CODE INDEX

Diagnostic Instructions

1. Perform the «Diagnostic System Check - Vehicle»(/gmc/sierra-2500/2012-2012/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures) prior to using this diagnostic procedure.
2. Review «Strategy Based Diagnosis»(/gmc/sierra-2500/2012-2012/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»(/gmc/sierra-2500/2012-2012/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__diagnostic-procedure-instructions) provides an overview of each diagnostic category.

Diagnostic Fault Information

Circuit/System Description

Air Temperature Sensors

The air temperature sensors are a 2-wire negative temperature co-efficient thermistor. The vehicle uses the following air temperature sensors

1. Ambient Air Temperature Sensor
2. Inside Air Temperature Sensor Assembly
3. Upper Left Air Temperature Sensor
4. Upper Right Air Temperature Sensor
5. Lower Left Air Temperature Sensor
6. Lower Right Air Temperature Sensor

A signal and low reference circuit enables the sensor to operate. As the air temperature surrounding the sensor increases, the sensor resistance decreases. The sensor signal voltage decreases as the resistance decreases. The sensor operates within a temperature range between -40 to +101°C (-40 to +215°F). The sensor signal varies between 0-5 volts. The HVAC control module converts the signal to a range between 0-255 counts. As the air temperature increases the count value will decrease. If the HVAC control module or auxiliary HVAC control module detects a malfunctioning sensor, then the control module software will use a defaulted air temperature value. The default value for the duct air temperature sensors will be displayed on the scan tool. The default value for the ambient and inside air temperature sensors will not be displayed on the scan tool. The scan tool parameter for the ambient and inside air temperature sensors are the actual state of the signal circuit. The default action ensures that the HVAC system can adjust the inside air temperature near the desired temperature until the condition is corrected.

Diagnostic Aids

Ambient Air Temperature Display Update

Conditions for Running the DTC

Ignition ON.

Conditions for Setting the DTC

The HVAC control module detects the temperature sensor signal circuit is less than -35°C (-39°F) or greater than 85°C (185°F) for greater than 15 seconds.

Action Taken When the DTC Sets

The system operates using a default value.

Conditions for Clearing the DTC

1. The DTC will become history if the HVAC control module no longer detects the condition that set the DTC.
2. The history DTC will clear after 100 fault-free ignition cycles have occurred.

Reference Information

Schematic Reference

HVAC Schematics

Connector End View Reference

WIRING SYSTEMS AND POWER MANAGEMENT - COMPONENT CONNECTOR END VIEWS - INDEX

Description and Operation

1. «Air Temperature Description and Operation»(/gmc/sierra-2500/2012-2012/remont/automatic-hvac-system/#hvac-system-automatic__air-temperature-description-and-operation)
2. «Air Delivery Description and Operation»(/gmc/sierra-2500/2012-2012/remont/automatic-hvac-system/#hvac-system-automatic__air-delivery-description-and-operation)

Electrical Information Reference

1. «Circuit Testing»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__circuit-testing)
2. «Connector Repairs»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__connector-repairs)
3. «Testing for Intermittent Conditions and Poor Connections»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__testing-for-intermittent-conditions-and-poor)
4. «Wiring Repairs»(/gmc/sierra-2500/2012-2012/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 Testing

1. Ignition OFF, all vehicle systems OFF, and the scan tool disconnected, disconnect the harness connector at the appropriate temperature sensor. It may take up to 2 minutes for all vehicle systems to power down.
2. Test for less than 5 ohms between the low reference circuit terminal listed below and ground: Ambient air temperature sensor terminal B Inside air temperature sensor terminal D Left upper air temperature sensor terminal A Right upper air temperature sensor terminal A Left lower air temperature sensor terminal A Right lower air temperature sensor terminal A If 5 ohms or greater Ignition OFF, disconnect the X2 harness connector at the HVAC control module. Test for less than 2 ohms in the low reference circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, replace the HVAC control module. If less than 5 ohms
3. Ignition ON.
4. Test for 4.8-5.2 V between the signal circuit terminal listed below and ground: Ambient air temperature sensor terminal A Inside air temperature sensor terminal A Left upper air temperature sensor terminal B Right upper air temperature sensor terminal B Left lower air temperature sensor terminal B Right lower air temperature sensor terminal B If less than 4.8 V Ignition OFF, disconnect the appropriate X1, X2, or X3 harness connector at the HVAC control module. Test for infinite resistance between the signal circuit and ground. If less than infinite resistance, repair the short to ground on the circuit. If infinite resistance Test for less than 2 ohms in the signal circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, replace the HVAC control module. If greater than 5.2 V Ignition OFF, disconnect the appropriate X1, X2, or X3 harness connector at the HVAC control module. Test for less than 1 V between the signal circuit and ground. If 1 V or greater, repair the short to voltage on the circuit. If less than 1 V, replace the HVAC control module. If between 4.8-5.2 V
5. Replace the temperature sensor.
6. Verify the DTC does not set while operating the vehicle under the Conditions for Running the DTC. If the DTC sets Replace the HVAC control module. If the DTC does not set
7. All OK.

Component Testing

1. Ignition OFF, disconnect the harness connector at the appropriate temperature sensor.
2. Test for the appropriate resistance value between the signal and the low reference terminals. Refer to «Sensor Resistance Table»(/gmc/sierra-2500/2012-2012/remont/automatic-hvac-system/#hvac-system-automatic__sensor-resistance-table) for resistance values. If not within 10 % of the specified value Replace the temperature sensor. If within 10 % of the specified value
3. All OK.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the repair.

1. «Duct Air Temperature Sensor Replacement - Upper Right Side»(/gmc/sierra-2500/2012-2012/remont/automatic-hvac-system/#hvac-system-automatic)
2. «Duct Air Temperature Sensor Replacement - Upper Left Side»(/gmc/sierra-2500/2012-2012/remont/automatic-hvac-system/#hvac-system-automatic)
3. «Duct Air Temperature Sensor Replacement - Lower Left Side»(/gmc/sierra-2500/2012-2012/remont/automatic-hvac-system/#hvac-system-automatic)
4. «Duct Air Temperature Sensor Replacement - Lower Right Side»(/gmc/sierra-2500/2012-2012/remont/automatic-hvac-system/#hvac-system-automatic)
5. «Ambient Air Temperature Sensor Replacement»(/gmc/sierra-2500/2012-2012/remont/automatic-hvac-system/#hvac-system-automatic)
6. «Inside Air Temperature Sensor Replacement»(/gmc/sierra-2500/2012-2012/remont/automatic-hvac-system/#hvac-system-automatic)
7. «Control Module References»(/gmc/sierra-2500/2012-2012/remont/communication-devices/#programming-and-setup-all-systems__control-module-references) for HVAC control module replacement, programming and setup

1. Perform the «Diagnostic System Check - Vehicle»(/gmc/sierra-2500/2012-2012/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures) prior to using this diagnostic procedure.
2. Review «Strategy Based Diagnosis»(/gmc/sierra-2500/2012-2012/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»(/gmc/sierra-2500/2012-2012/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__diagnostic-procedure-instructions) provides an overview of each diagnostic category.

Circuit Description

The sunload sensor is a 2-wire photo diode. The vehicle uses left and right sunload sensors. The two sensors are integrated into the sunload sensor assembly along with the ambient light sensor. Ground and signal circuits enable the sensors to operate. As the sunload increases, the sensor signal decreases. The sensor signal varies between 0 and 5 volts. The HVAC control module converts the signal to a range between 0 and 255 counts. The sunload sensor provides the HVAC control module with a measurement of the amount of light shining on the vehicle. Bright or high intensity light causes the vehicles interior temperature to increase. The HVAC system compensates for the increased temperature by diverting additional cool air into the vehicle.

The following DTCs are for the left and right sunload sensors.

1. B0183 is for the driver sunload sensor.
2. B0188 is for the passenger sunload sensor.

Ignition ON.

The HVAC control module detects the signal circuit is less than 5 counts or greater than 250 counts.

1. The driver information center (DIC) will display SERVICE A/C SYSTEM.
2. The system will operate as if no sunload condition exists.

1. The DTC will become history if the HVAC control module no longer detects the condition that set the DTC.
2. The history DTC will clear after 100 fault-free ignition cycles have occurred.

Schematic Reference

HVAC Schematics

Connector End View Reference

WIRING SYSTEMS AND POWER MANAGEMENT - COMPONENT CONNECTOR END VIEWS - INDEX

Description and Operation

1. «Air Temperature Description and Operation»(/gmc/sierra-2500/2012-2012/remont/automatic-hvac-system/#hvac-system-automatic__air-temperature-description-and-operation)
2. «Air Delivery Description and Operation»(/gmc/sierra-2500/2012-2012/remont/automatic-hvac-system/#hvac-system-automatic__air-delivery-description-and-operation)

Electrical Information Reference

1. «Circuit Testing»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__circuit-testing)
2. «Connector Repairs»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__connector-repairs)
3. «Testing for Intermittent Conditions and Poor Connections»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__testing-for-intermittent-conditions-and-poor)
4. «Wiring Repairs»(/gmc/sierra-2500/2012-2012/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

Ignition ON, observe the appropriate scan tool Sunload Sensor parameter. The reading should be between 5 and 250 counts and change with sunlight intensity.

1. Ignition OFF and all vehicle systems OFF, disconnect the harness connector at the ambient light/sunload sensor. It may take up to 2 minutes for all vehicle systems to power down.
2. Test for less than 10 ohms between the ground circuit terminal C and ground. If 10 ohms or greater Ignition OFF, disconnect the X1 harness connector at the HVAC control module. Test for less than 2 ohms in the ground circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, repair the open/high resistance in the ground connection. If less than 10 ohms
3. Ignition ON.
4. Test for 4.8-5.2 V between the ground circuit terminal C and the signal circuit terminals listed below: Driver sunload sensor signal terminal A. Passenger sunload sensor signal terminal B. If less than 4.8 V Ignition OFF, disconnect the appropriate X1 harness connector at the HVAC control module. Test for infinite resistance between the signal circuit and ground. If less than infinite resistance, repair the short to ground on the circuit. If infinite resistance Test for less than 2 ohms in the signal circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, replace the HVAC control module. If greater than 5.2 V Ignition OFF, disconnect the appropriate X1 harness connector at the HVAC control module. Test for less than 1 V between the signal circuit and ground. If 1 V or greater, repair the short to voltage on the circuit. If less than 1 V, replace the HVAC control module. If between 4.8-5.2 V
5. Test or replace the ambient light/sunload sensor.
6. Verify the DTC does not set when operating the vehicle under the Conditions for Running the DTC. If the DTC sets Replace the HVAC control module. If the DTC does not set
7. All OK.

Perform the Diagnostic Repair Verification after completing the repair.

1. «Sun Load Temperature Sensor Replacement»(/gmc/sierra-2500/2012-2012/remont/automatic-hvac-system/#hvac-system-automatic)
2. «Control Module References»(/gmc/sierra-2500/2012-2012/remont/communication-devices/#programming-and-setup-all-systems__control-module-references) for HVAC control module replacement, programming and setup

1. Perform the «Diagnostic System Check - Vehicle»(/gmc/sierra-2500/2012-2012/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures) prior to using this diagnostic procedure.
2. Review «Strategy Based Diagnosis»(/gmc/sierra-2500/2012-2012/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»(/gmc/sierra-2500/2012-2012/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__diagnostic-procedure-instructions) provides an overview of each diagnostic category.

The HVAC control module controls the HVAC door actuators to regulate the airflow through the HVAC system. Each actuator consists of an electric motor and a potentiometer. The module supplies a low reference and 5 V reference source voltage to the potentiometer. The HVAC control module monitors the voltage drop across the potentiometer on the door position signal circuit. When the actuator shaft rotates, the voltage on the door position signal circuit changes. The control circuit uses either a 0, 2.5 or 5 V signal to command the actuator movement. When the actuator is at rest, the control circuit value is 2.5 V. When actuator movement is commanded in one direction the voltage toggles between 2.5-5 V, then, when commanded in the opposite direction the voltage toggles between 2.5-0 V.

1. B0228 is for the recirculation actuator.
2. B0413 is for the drivers air temperature actuator.
3. B0423 is for the passenger air temperature actuator.
4. B3779 is for the mode actuator.

1. Ignition ON.
2. The HVAC module is ON.

The actual door position differs from the commanded door position by more than 4 counts or the HVAC control module detects the door position signal circuit is less than 3 counts or greater than 253 counts.

The control circuit is deactivated for the appropriate actuator.

1. The DTC becomes history when the HVAC control module no longer detects the condition that set the DTC.
2. The history DTC will clear after 100 fault-free ignition cycles have occurred.

Not all intermittent conditions will cause a DTC to be stored.

Reposition tightly pulled wire harness actuator connections to relieve taught wires at connectors, and apply dielectric grease to actuator terminals to eliminate/minimize intermittent conditions.

Wiggle the harness near the connector to inspect terminal joints for loose connections.

Schematic Reference

HVAC Schematics

Connector End View Reference

WIRING SYSTEMS AND POWER MANAGEMENT - COMPONENT CONNECTOR END VIEWS - INDEX

Description and Operation

1. «Air Delivery Description and Operation»(/gmc/sierra-2500/2012-2012/remont/automatic-hvac-system/#hvac-system-automatic__air-delivery-description-and-operation)
2. «Air Temperature Description and Operation»(/gmc/sierra-2500/2012-2012/remont/automatic-hvac-system/#hvac-system-automatic__air-temperature-description-and-operation)

Electrical Information Reference

1. «Circuit Testing»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__circuit-testing)
2. «Connector Repairs»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__connector-repairs)
3. «Testing for Intermittent Conditions and Poor Connections»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__testing-for-intermittent-conditions-and-poor)
4. «Wiring Repairs»(/gmc/sierra-2500/2012-2012/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 appropriate actuator in both directions with a scan tool. The scan tool door position parameter reading should be between 3 and 253 counts.

Note. Refer to bulletin 09-06-03-004 before replacing any components.

1. Ignition OFF, disconnect the harness connector at the appropriate actuator.
2. Test for less than 40 ohms between the low reference circuit terminal 7 and ground. If 40 ohms or greater Ignition OFF, disconnect the X3 harness connector at the HVAC control module. Test for less than 2 ohms in the low reference circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, replace the HVAC control module. If less than 40 ohms
3. Ignition ON.
4. Verify that a test lamp illuminates between the ignition circuit terminal 5 and ground. If the test lamp does not illuminate and the circuit fuse is good Ignition OFF. Test for less than 2 ohms in the ignition circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, verify the fuse is OK and there is voltage at the fuse. If the test lamp does not illuminate and the circuit fuse is open Ignition OFF. Test for infinite resistance between the ignition circuit and ground. If less than infinite resistance, repair the short to ground on the circuit. If infinite resistance, replace the actuator. If the test lamp illuminates
5. Test for 4.8-5.2 V between the 5 V reference circuit terminal 10 and ground. If less than 4.8 V Ignition OFF, disconnect the X3 harness connector at the HVAC control module. Test for infinite resistance between the 5 V reference circuit and ground. If less than infinite resistance, repair the short to ground on the circuit. If infinite resistance Test for less than 2 ohms in the 5 V reference circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, replace the HVAC control module. If greater than 5.2 V Ignition OFF, disconnect the X3 harness connector at the HVAC control module, ignition ON. Test for less than 1 V between the 5 V reference circuit and ground. If 1 V or greater, repair the short to voltage on the circuit. If less than 1 V, replace the HVAC control module. If between 4.8-5.2 V
6. Verify the appropriate scan tool parameter listed below is greater than 250 counts: Mode Door Actual Right Temp. Dr. Actual Air Inlet. Dr. Actual Left Temp. Dr. Actual If 250 counts or less Ignition OFF, disconnect the harness connector at the HVAC control module. Test for infinite resistance between the signal circuit and ground. If less than infinite resistance, repair the short to ground on the circuit. If infinite resistance, replace the HVAC control module. If greater than 250 counts
7. Install a 3 A fused jumper wire between the signal circuit terminal 9 and the low reference circuit terminal 7.
8. Verify the appropriate scan tool parameter listed below is less than 5 counts. Mode Door Actual Right Temp. Dr. Actual Air Inlet Dr. Actual Left Temp. Dr. Actual If 5 counts or greater Ignition OFF, disconnect the X3 harness connector at the HVAC control module, ignition ON. Test for less than 1 V between the signal circuit and ground. If 1 V or greater, repair the short to voltage on the circuit. If less than 1 V Ignition OFF. Test for less than 2 ohms in the signal circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, replace the HVAC control module. If less than 5 counts
9. Test for 2.2-2.8 V between the control circuit terminal 6 and ground. If less than 2.2 V Ignition OFF, disconnect the X3 harness connector at the HVAC control module. Test for infinite resistance between the control circuit and ground. If less than infinite resistance, repair the short to ground on the circuit. If infinite resistance Test for less than 2 ohms in the control circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, replace the HVAC control module. If greater than 2.8 V Ignition OFF, disconnect the X3 harness connector at the HVAC control module, ignition ON. Test for less than 1 V between the control circuit and ground. If 1 V or greater, repair the short to voltage on the circuit. If less than 1 V, replace the HVAC control module. If between 2.2-2.8 V
10. Verify the voltage reading toggles when commanding the appropriate actuator listed below in both directions with a scan tool. Air Inlet Door Left Temp. Door Position Mode Door Position Right Temp. Door Position If the voltage does not toggle Replace the HVAC control module. If voltage toggles
11. Test or replace the actuator.

Perform the Diagnostic Repair Verification after completing the repair.

1. «Air Inlet Valve Actuator Replacement»(/gmc/sierra-2500/2012-2012/remont/automatic-hvac-system/#hvac-system-automatic)
2. «Mode Valve Actuator Replacement»(/gmc/sierra-2500/2012-2012/remont/automatic-hvac-system/#hvac-system-automatic)
3. «Temperature Valve Actuator Replacement - Left Side»(/gmc/sierra-2500/2012-2012/remont/automatic-hvac-system/#hvac-system-automatic)
4. «Temperature Valve Actuator Replacement - Right Side»(/gmc/sierra-2500/2012-2012/remont/automatic-hvac-system/#hvac-system-automatic)
5. «Control Module References»(/gmc/sierra-2500/2012-2012/remont/communication-devices/#programming-and-setup-all-systems__control-module-references) for HVAC control module replacement, programming and setup

1. Perform the «Diagnostic System Check - Vehicle»(/gmc/sierra-2500/2012-2012/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures) prior to using this diagnostic procedure.
2. Review «Strategy Based Diagnosis»(/gmc/sierra-2500/2012-2012/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»(/gmc/sierra-2500/2012-2012/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__diagnostic-procedure-instructions) provides an overview of each diagnostic category.

This DTC is not associated with any wiring. It is an internal fault inside the HVAC control module for a stuck or shorted control button.

Battery voltage is between 9-16 V and data link communications operate normally.

The HVAC control module has internal fault inside the HVAC control module for a stuck or shorted control button.

1. The DTC will become history if the HVAC module no longer detects a failure.
2. The history DTC will clear after 40 consecutive fault free ignition cycles have occurred.

1. Ignition ON
2. Verify DTC B1023 is not set. If DTC B1023 is set Program the K33 HVAC control module. Verify the DTC does not set. If the DTC sets, replace the K33 HVAC control module. If the DTC does not set All OK If DTC B1023 is not set
3. All OK

Perform the Diagnostic Repair Verification after completing the repair.

Control Module References for control module replacement, programming, and setup

1. Perform the «Diagnostic System Check - Vehicle»(/gmc/sierra-2500/2012-2012/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures) prior to using this diagnostic procedure.
2. Review «Strategy Based Diagnosis»(/gmc/sierra-2500/2012-2012/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»(/gmc/sierra-2500/2012-2012/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__diagnostic-procedure-instructions) provides an overview of each diagnostic category.

The HVAC control module supplies the evaporator air temperature sensor with a low reference circuit and 5 V signal circuit. The HVAC control module determines the voltage drop across the sensor, which is proportional to temperature. As the air temperature increases, the sensor resistance decreases and the voltage signal decreases. As the air temperature decreases, the sensor resistance increases and the voltage signal increases.

The ignition is turned ON.

The HVAC control module detects the evaporator air temperature sensor signal circuit is less than -36°C (-38°F) or more than 215°C (419°F) for more than 15 seconds.

The A/C compressor will be disabled.

1. The DTC will become history if the HVAC control module no longer detects a failure.
2. The history DTC will clear after 100 fault-free ignition cycles.

Schematic Reference

HVAC Schematics

Connector End View Reference

WIRING SYSTEMS AND POWER MANAGEMENT - COMPONENT CONNECTOR END VIEWS - INDEX

Description and Operation

1. «Air Temperature Description and Operation»(/gmc/sierra-2500/2012-2012/remont/automatic-hvac-system/#hvac-system-automatic__air-temperature-description-and-operation)
2. «Air Delivery Description and Operation»(/gmc/sierra-2500/2012-2012/remont/automatic-hvac-system/#hvac-system-automatic__air-delivery-description-and-operation)

Electrical Information Reference

1. «Circuit Testing»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__circuit-testing)
2. «Connector Repairs»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__connector-repairs)
3. «Testing for Intermittent Conditions and Poor Connections»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__testing-for-intermittent-conditions-and-poor)
4. «Wiring Repairs»(/gmc/sierra-2500/2012-2012/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
2. Verify the scan tool A/C Evaporator Temperature Sensor parameter is between-35°C (-39°F) and 85°C (185°F) and changes with evaporator air temperature changes. If not between -35°C (-39°F) and 85°C (185°F) or does not change Refer to Circuit/System Testing below. If between -35°C (-39°F) and 85°C (185°F) changes
3. All OK

1. Ignition OFF and all vehicle systems OFF, disconnect the harness connector at the evaporator air temperature sensor. It may take up to 2 minutes for all vehicle systems to power down.
2. Test for less than 5 ohms between the low reference circuit terminal B and ground. If 5 ohms or greater Ignition OFF, disconnect the X3 harness connector at the HVAC control module. Test for less than 2 ohms in the low reference circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, replace the HVAC control module. If less than 5 ohms
3. Ignition ON
4. Verify the scan tool A/C Evaporator Temperature Sensor parameter is less than -35°C (-39°F). If -35°C (-39°F) or greater Ignition OFF, disconnect the X3 harness connector at the HVAC control module. Test for infinite resistance between the signal circuit terminal A and ground. If less than infinite resistance, repair the short to ground on the circuit. If infinite resistance, replace the HVAC control module. If less than -35°C (-39°F)
5. Install a 3 A fused jumper wire between the signal circuit terminal A and the low reference circuit terminal B.
6. Verify the scan tool A/C Evaporator Temperature Sensor parameter is greater than 85°C (185°F). If 85°C (185°F) or less Ignition OFF, disconnect the X3 harness connector at the HVAC control module, Ignition ON. Test for less than 1 V between the signal circuit terminal A and ground. If 1 V or greater, repair the short to voltage on the circuit. If less than 1 V Test for less than 2 ohms in the signal circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, replace the HVAC control module. If greater than 85°C (185°F)
7. Test or replace the evaporator air temperature sensor.

1. Ignition OFF, disconnect the harness connector at the evaporator temperature sensor.
2. Measure the resistance between terminal A and terminal B.
3. Verify the resistance is within 5 % of the specified readings contained in the «Sensor Resistance Table»(/gmc/sierra-2500/2012-2012/remont/automatic-hvac-system/#hvac-system-automatic__sensor-resistance-table) . If not within 5 % Replace the evaporator air temperature sensor If within 5 %
4. All OK.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

1. «Air Conditioning Refrigerant Temperature Sensor Replacement»(/gmc/sierra-2500/2012-2012/remont/automatic-hvac-system/#hvac-system-automatic)
2. «Control Module References»(/gmc/sierra-2500/2012-2012/remont/communication-devices/#programming-and-setup-all-systems__control-module-references) for HVAC control module replacement, setup, and programming

1. Perform the «Diagnostic System Check - Vehicle»(/gmc/sierra-2500/2012-2012/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures) prior to using this diagnostic procedure.
2. Review «Strategy Based Diagnosis»(/gmc/sierra-2500/2012-2012/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»(/gmc/sierra-2500/2012-2012/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__diagnostic-procedure-instructions) provides an overview of each diagnostic category.

The engine control module (ECM) monitors the high side refrigerant pressure through the A/C refrigerant pressure sensor. The ECM supplies a 5 V 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 V.

1. The ECM detects that the A/C pressure is less than 1 psi (0.01 V) sets DTC P0532.
2. The ECM detects that the A/C pressure is more than 428 psi (4.92 V) 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 DTC will become history if the ECM no longer detects a failure.
2. The history DTC will clear after 40 consecutive fault free ignition cycles have occurred.

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

Schematic Reference

HVAC Schematics

Connector End View Reference

WIRING SYSTEMS AND POWER MANAGEMENT - COMPONENT CONNECTOR END VIEWS - INDEX

Description and Operation

1. «Air Temperature Description and Operation»(/gmc/sierra-2500/2012-2012/remont/automatic-hvac-system/#hvac-system-automatic__air-temperature-description-and-operation)
2. «Air Delivery Description and Operation»(/gmc/sierra-2500/2012-2012/remont/automatic-hvac-system/#hvac-system-automatic__air-delivery-description-and-operation)

Electrical Information Reference

1. «Circuit Testing»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__circuit-testing)
2. «Connector Repairs»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__connector-repairs)
3. «Testing for Intermittent Conditions and Poor Connections»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__testing-for-intermittent-conditions-and-poor)
4. «Wiring Repairs»(/gmc/sierra-2500/2012-2012/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
2. Verify DTC P0641 is not set. If DTC P0641 is set Refer to «Diagnostic Trouble Code (DTC) List - Vehicle»(/gmc/sierra-2500/2012-2012/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__diagnostic-trouble-code-dtc-list) . If DTC P0641 is not set
3. Refer to Circuit/System Testing below.

1. Ignition OFF and all vehicle systems OFF, disconnect the harness connector at the A/C refrigerant pressure sensor. It may take up to 2 minutes for all vehicle systems to power down.
2. Test for less than 5 ohms between the low reference circuit terminal 1 and ground. If 5 ohms or greater Ignition OFF, disconnect the X1 harness connector at the HVAC control module. Test for less than 2 ohms in the low reference circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, replace the HVAC control module. If less than 5 ohms
3. Disconnect the X1 harness connector at the ECM.
4. Test for infinite resistance between the low reference circuit terminal 13 and ground. If less than infinite resistance Repair the short to ground on the circuit. If infinite resistance
5. Ignition ON
6. Test for 4.8-5.2 V between the 5 V reference circuit terminal 2 and ground. If less than 4.8 V Ignition OFF, disconnect the X1 harness connector at the HVAC control module. Test for infinite resistance between the 5 V reference circuit and ground. If less than infinite resistance, repair the short to ground on the circuit. If infinite resistance Test for less than 2 ohms on the 5 V reference circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, replace the HVAC control module. If greater than 5.2 V Ignition OFF, disconnect the X1 harness connector at the HVAC control module, ignition ON. Test for less than 1 V between the 5 V reference circuit and ground. If 1 V or greater, repair the short to voltage on the circuit. If less than 1 V, replace the HVAC control module. If between 4.8-5.2 V
7. Verify the scan tool A/C High Side Pressure Sensor parameter is less than 0.1 V (1 psi). If 0.1 V (1 psi) or greater Ignition OFF, disconnect the X1 harness connector at the HVAC control module, ignition ON. Test for less than 1 V between the signal circuit terminal 3 and ground. If greater than 1 V, repair the short to voltage on the circuit. If less than 1 V, replace the HVAC control module. If less than 0.1 V (1 psi)
8. Install a 3 A fused jumper wire between the signal circuit terminal 3 and the 5 V reference circuit terminal 2.
9. Verify the scan tool A/C High Side Pressure Sensor parameter is greater than 4.9 V (490 psi). If 4.9 V (490 psi) or less Ignition OFF, disconnect the X1 harness connector at the HVAC control module. Test for infinite resistance between the signal circuit and ground. If less than infinite resistance, repair the short to ground on the circuit. If infinite resistance Test for less than 2 ohms on the signal circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, replace the HVAC control module. If greater than 4.9 V (490 psi)
10. Test or replace the A/C refrigerant pressure sensor.

Perform the Diagnostic Repair Verification after completing the repair.

1. «Air Conditioning (A/C) Refrigerant Pressure Sensor Replacement (Non-HP2)»(/gmc/sierra-2500/2012-2012/remont/automatic-hvac-system/#heating-ventilation-and-air-conditioning__air-conditioning-ac-refrigerant-pressure-sensor) , «Air Conditioning (A/C) Refrigerant Pressure Sensor Replacement (LGH, LML)»(/gmc/sierra-2500/2012-2012/remont/automatic-hvac-system/#heating-ventilation-and-air-conditioning)
2. «Control Module References»(/gmc/sierra-2500/2012-2012/remont/communication-devices/#programming-and-setup-all-systems__control-module-references) for the ECM replacement, programming, and setup

1. Perform the «Diagnostic System Check - Vehicle»(/gmc/sierra-2500/2012-2012/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures) prior to using this diagnostic procedure.
2. Review «Strategy Based Diagnosis»(/gmc/sierra-2500/2012-2012/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»(/gmc/sierra-2500/2012-2012/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__diagnostic-procedure-instructions) provides an overview of each diagnostic category.

Circuit System Description

Ignition voltage is supplied directly to the A/C compressor clutch relay. The engine control module (ECM) controls the relay by grounding the A/C clutch relay control circuit. When the ECM is commanding a component ON, the voltage of the control circuit should be near 0 volt. When the ECM is commanding the control circuit to a component OFF, the voltage potential of the circuit should be near battery voltage.

1. The ignition voltage is between 11-18 volts.
2. The engine speed is greater than 600 RPM.
3. An A/C request is made.

Conditions for Setting the DTCs

The ECM detects an open, short to ground, or short to voltage on the control circuit of the A/C compressor clutch relay when commanded OFF with the engine in crank or run status.

The ECM will store conditions which were present when the DTC set as Failure Records data only. This information will not be stored as Freeze Frame data.

A history DTC clears after 40 consecutive warm-up cycles have occurred without a malfunction.

Schematic Reference

HVAC Schematics

Connector End View Reference

WIRING SYSTEMS AND POWER MANAGEMENT - COMPONENT CONNECTOR END VIEWS - INDEX

Description and Operation

1. «Air Delivery Description and Operation»(/gmc/sierra-2500/2012-2012/remont/automatic-hvac-system/#hvac-system-automatic__air-delivery-description-and-operation)
2. «Air Temperature Description and Operation»(/gmc/sierra-2500/2012-2012/remont/automatic-hvac-system/#hvac-system-automatic__air-temperature-description-and-operation)

Electrical Information Reference

1. «Circuit Testing»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__circuit-testing)
2. «Connector Repairs»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__connector-repairs)
3. «Testing for Intermittent Conditions and Poor Connections»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__testing-for-intermittent-conditions-and-poor)
4. «Wiring Repairs»(/gmc/sierra-2500/2012-2012/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. Feel/listen for the A/C relay to click.

1. Ignition OFF, disconnect the A/C compressor relay.
2. Ignition ON.
3. Verify that a test lamp illuminates between the ignition circuit terminal 86 and ground. If the test lamp does not illuminate Repair the open/high resistance in the circuit. If the test lamp illuminates
4. Verify that a test lamp illuminates between the relay B+ circuit terminal 30 and ground. If the test lamp does not illuminate Replace the underhood fuse block. If the test lamp illuminates
5. Connect a test lamp between the ignition circuit terminal 86 and the control circuit terminal 85.
6. Verify the test lamp turns ON and OFF when commanding the A/C relay ON and OFF with a scan tool. If the test lamp is always OFF Ignition OFF, disconnect the X1 harness connector at the engine control module, ignition ON. Test for less than 1 V between the control circuit and ground. If 1 V or greater, repair the short to voltage on the circuit. If less than 1 V Ignition OFF. Test for less than 2 ohms in the control circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, replace the engine control module. If the test lamp is always ON Ignition OFF, disconnect the X1 harness connector at the engine control module. Test for infinite resistance between the control circuit and ground. If less than infinite resistance, repair the short to ground on the circuit. If infinite resistance, replace the engine control module. If the test lamp turns ON and OFF
7. Verify that a test lamp does not illuminate between the control circuit terminal 87 and ground. If the test lamp illuminates Repair the short to voltage on the circuit. If the test lamp does not illuminate
8. Ignition OFF and all vehicle systems OFF, disconnect the harness connector at the A/C compressor clutch. It may take up to 2 minutes for all vehicle systems to power down.
9. Test for less than 5 ohms between the ground circuit terminal A and ground. If 5 ohms or greater Ignition OFF. Test for less than 2 ohms in the ground circuit end to end. If 2 ohms or greater, repair the open/high resistance in the ground circuit. If less than 2 ohms, repair the open/high resistance in the ground connection. If less than 5 ohms
10. Connect the harness connector at the A/C compressor clutch.
11. Ignition ON, connect a 10 A fused jumper wire between the B+ circuit terminal 30 and control circuit terminal 87.
12. Verify the A/C compressor clutch is activated. If the A/C compressor clutch does not activate Ignition OFF. Test for less than 2 ohms in the control circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, test or replace the A/C compressor clutch. If the A/C compressor clutch activates
13. Test or replace the A/C compressor relay.

1. Ignition OFF, disconnect the A/C compressor relay.
2. Test for 60-180 ohms between terminals 85 and 86. If less than 60 ohms or greater than 180 ohms Replace the A/C compressor relay. If between 60-180 ohms
3. Test for infinite resistance between the terminals listed below: 30 and 86 30 and 87 30 and 85 85 and 87 If less than infinite resistance Replace the A/C compressor relay. If infinite resistance
4. Install a 30 A fused jumper wire between relay terminal 86 and 12 V. Install a jumper wire between relay terminal 85 and ground. Test for less than 2 ohms between terminals 30 and 87.
5. Test for less than 2 ohms between terminals 30 and 87. If 2 ohms or greater Replace the A/C compressor relay. If less than 2 ohms
6. All OK.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

1. «Relay Replacement (Within an Electrical Center)»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-repair-instructions__relay-replacement-within-an-electrical-center) , «Relay Replacement (Attached to Wire Harness)»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-repair-instructions)
2. «Control Module References»(/gmc/sierra-2500/2012-2012/remont/communication-devices/#programming-and-setup-all-systems__control-module-references) for ECM replacement, setup, and programming

Symptoms - HVAC Systems - Automatic

Visual/Physical Inspection

1. Inspect for aftermarket devices which could affect the operation of the HVAC System. Refer to «Checking Aftermarket Accessories»(/gmc/sierra-2500/2012-2012/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»(/gmc/sierra-2500/2012-2012/remont/automatic-hvac-system/#hvac-system-automatic__air-temperature-description-and-operation) .
5. The following could 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. «Blower Motor Malfunction»(/gmc/sierra-2500/2012-2012/remont/automatic-hvac-system/#hvac-system-automatic)
2. «Air Conditioning Compressor Malfunction»(/gmc/sierra-2500/2012-2012/remont/automatic-hvac-system/#hvac-system-automatic)
3. «Air Temperature Malfunction»(/gmc/sierra-2500/2012-2012/remont/automatic-hvac-system/#hvac-system-automatic)
4. «Leak Testing»(/gmc/sierra-2500/2012-2012/remont/automatic-hvac-system/#heating-ventilation-and-air-conditioning)
5. «Noise Diagnosis - HVAC Module»(/gmc/sierra-2500/2012-2012/remont/automatic-hvac-system/#heating-ventilation-and-air-conditioning__noise-diagnosis-hvac-module)
6. «Noise Diagnosis - Air Conditioning (A/C) System»(/gmc/sierra-2500/2012-2012/remont/automatic-hvac-system/#heating-ventilation-and-air-conditioning__noise-diagnosis-air-conditioning-ac)
7. «Noise Diagnosis - Blower Motor»(/gmc/sierra-2500/2012-2012/remont/automatic-hvac-system/#heating-ventilation-and-air-conditioning__noise-diagnosis-blower-motor)
8. «Odor Diagnosis»(/gmc/sierra-2500/2012-2012/remont/automatic-hvac-system/#heating-ventilation-and-air-conditioning__odor-diagnosis)

1. Perform the «Diagnostic System Check - Vehicle»(/gmc/sierra-2500/2012-2012/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures) prior to using this diagnostic procedure.
2. Review «Strategy Based Diagnosis»(/gmc/sierra-2500/2012-2012/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»(/gmc/sierra-2500/2012-2012/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__diagnostic-procedure-instructions) provides an overview of each diagnostic category.

When the A/C switch is pressed, the HVAC control module grounds the A/C request signal circuit. This input will request the ECM to ground the A/C compressor clutch relay control circuit, which will switch the A/C compressor 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 to turn on the 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 greater than 600 RPM
4. Engine speed is less than 4, 760 RPM
5. A/C high side pressure is between 2929-269 kPa (39-425 psi)
6. Throttle position is less than 100 percent
7. Evaporator temperature is greater than 2°C (34°F)
8. ECM does not detect excessive torque load
9. ECM does not detect insufficient idle quality
10. The ambient temperature is above 1°C (34°F)

Schematic Reference

HVAC Schematics

Connector End View Reference

WIRING SYSTEMS AND POWER MANAGEMENT - COMPONENT CONNECTOR END VIEWS - INDEX

Description and Operation

1. «Air Temperature Description and Operation»(/gmc/sierra-2500/2012-2012/remont/automatic-hvac-system/#hvac-system-automatic__air-temperature-description-and-operation)
2. «Air Delivery Description and Operation»(/gmc/sierra-2500/2012-2012/remont/automatic-hvac-system/#hvac-system-automatic__air-delivery-description-and-operation)

Electrical Information Reference

1. «Circuit Testing»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__circuit-testing)
2. «Connector Repairs»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__connector-repairs)
3. «Testing for Intermittent Conditions and Poor Connections»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__testing-for-intermittent-conditions-and-poor)
4. «Wiring Repairs»(/gmc/sierra-2500/2012-2012/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. Feel/listen for the A/C relay to click.

1. Ignition OFF, disconnect the A/C compressor relay.
2. Ignition ON.
3. Verify that a test lamp illuminates between the ignition circuit terminal 86 and ground. If the test lamp does not illuminate Repair the open/high resistance in the circuit. If the test lamp illuminates
4. Verify that a test lamp illuminates between the relay B+ circuit terminal 30 and ground. If the test lamp does not illuminate Replace the underhood fuse block. If the test lamp illuminates
5. Connect a test lamp between the ignition circuit terminal 86 and the control circuit terminal 85.
6. Verify the test lamp turns ON and OFF when commanding the A/C relay ON and OFF with a scan tool. If the test lamp is always OFF Ignition OFF, disconnect the X1 harness connector at the engine control module, ignition ON. Test for less than 1 V between the control circuit and ground. If 1 V or greater, repair the short to voltage on the circuit. If less than 1 V Ignition OFF. Test for less than 2 ohms in the control circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, replace the engine control module. If the test lamp is always ON Ignition OFF, disconnect the X1 harness connector at the engine control module. Test for infinite resistance between the control circuit and ground. If less than infinite resistance, repair the short to ground on the circuit. If infinite resistance, replace the engine control module. If the test lamp turns ON and OFF
7. Verify that a test lamp does not illuminate between the control circuit terminal 87 and ground. If the test lamp illuminates Repair the short to voltage on the circuit. If the test lamp does not illuminate
8. Ignition OFF and all vehicle systems OFF, disconnect the harness connector at the A/C compressor clutch. It may take up to 2 minutes for all vehicle systems to power down.
9. Test for less than 5 ohms between the ground circuit terminal A and ground. If 5 ohms or greater Ignition OFF. Test for less than 2 ohms in the ground circuit end to end. If 2 ohms or greater, repair the open/high resistance in the ground circuit. If less than 2 ohms, repair the open/high resistance in the ground connection. If less than 5 ohms
10. Connect the harness connector at the A/C compressor clutch.
11. Ignition ON, connect a 10 A fused jumper wire between the B+ circuit terminal 30 and control circuit terminal 87.
12. Verify the A/C compressor clutch is activated. If the A/C compressor clutch does not activate Ignition OFF. Test for less than 2 ohms in the control circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, test or replace the A/C compressor clutch. If the A/C compressor clutch activates
13. Test or replace the A/C compressor relay.

1. Ignition OFF, disconnect the A/C compressor relay.
2. Test for 60-180 ohms between terminals 85 and 86. If less than 60 ohms or greater than 180 ohms Replace the A/C compressor relay. If between 60-180 ohms
3. Test for infinite resistance between the terminals listed below: 30 and 86 30 and 87 30 and 85 85 and 87 If less than infinite resistance Replace the A/C compressor relay. If infinite resistance
4. Install a 30 A fused jumper wire between relay terminal 86 and 12 V. Install a jumper wire between relay terminal 85 and ground. Test for less than 2 ohms between terminals 30 and 87.
5. Test for less than 2 ohms between terminals 30 and 87. If 2 ohms or greater Replace the A/C compressor relay. If less than 2 ohms
6. All OK.

Perform the Diagnostic Repair Verification after completing the repair.

1. «Air Conditioning Compressor Replacement (LU3)»(/gmc/sierra-2500/2012-2012/remont/automatic-hvac-system/#heating-ventilation-and-air-conditioning__air-conditioning-compressor-replacement-lu3) , «Air Conditioning Compressor Replacement (LZ1, L20, LC9, L9H, L92, LMG)»(/gmc/sierra-2500/2012-2012/remont/automatic-hvac-system/#heating-ventilation-and-air-conditioning__air-conditioning-compressor-replacement-lz1-l20) , «Air Conditioning Compressor Replacement (LGH, LML)»(/gmc/sierra-2500/2012-2012/remont/automatic-hvac-system/#heating-ventilation-and-air-conditioning)
2. «Compressor Clutch Plate/Hub Assembly Replacement»(/gmc/sierra-2500/2012-2012/remont/automatic-hvac-system/#heating-ventilation-and-air-conditioning)
3. «Control Module References»(/gmc/sierra-2500/2012-2012/remont/communication-devices/#programming-and-setup-all-systems__control-module-references) for HVAC control module and ECM replacement, programming, and setup.

1. Perform the «Diagnostic System Check - Vehicle»(/gmc/sierra-2500/2012-2012/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures) prior to using this diagnostic procedure.
2. Review «Strategy Based Diagnosis»(/gmc/sierra-2500/2012-2012/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»(/gmc/sierra-2500/2012-2012/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__diagnostic-procedure-instructions) provides an overview of each diagnostic category.

The blower motor control module is an interface between the HVAC control module and the blower motor. The blower motor speed control, battery positive and ground circuits enable the control module to operate. The HVAC control module provides a variable voltage to the blower motor control module to request the selected blower speed. The blower motor control module provides a pulse width modulation (PWM) signal to the blower motor in order to control the blower motor speed. The module supplies 12 volts to the blower motor through the blower motor voltage supply circuit.

Prior to motor replacement connect a direct independent B+ and ground to verify operation.

Inspect the motor shaft for rust or other foreign material which may prohibit proper motor operation.

If the motor operates properly please reinstall it, check for PIs or TSBs, and refer to Testing for Intermittent Conditions and Poor Connections in the appropriate Electrical Information Reference section of this document.

Schematic Reference

HVAC Schematics

Connector End View Reference

WIRING SYSTEMS AND POWER MANAGEMENT - COMPONENT CONNECTOR END VIEWS - INDEX

Description and Operation

1. «Air Delivery Description and Operation»(/gmc/sierra-2500/2012-2012/remont/manual-hvac-system/#hvac-system-manual__air-delivery-description-and-operation)
2. «Air Temperature Description and Operation»(/gmc/sierra-2500/2012-2012/remont/manual-hvac-system/#hvac-system-manual__air-temperature-description-and-operation)

Electrical Information Reference

1. «Circuit Testing»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__circuit-testing)
2. «Connector Repairs»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__connector-repairs)
3. «Testing for Intermittent Conditions and Poor Connections»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__testing-for-intermittent-conditions-and-poor)
4. «Wiring Repairs»(/gmc/sierra-2500/2012-2012/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 OFF, and all vehicle systems OFF. Disconnect the X2 harness connector at the blower motor control module. It may take up to 2 minutes for all vehicle systems to power down.
2. Test for less than 5 ohms between the ground circuit terminal 5 and ground. If 5 ohms or greater Test for less than 2 ohms in the ground circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, repair the open/high resistance in the ground connection. If less than 5 ohms
3. Ignition ON
4. Verify a test lamp illuminates between the B+ circuit terminal 6 and ground. If the test lamp does not illuminate and the circuit fuse is good Ignition OFF Test for less than 2 ohms in the B+ circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, verify the fuse is not open and there is voltage at the fuse. If the test lamp does not illuminate and the circuit fuse is open Ignition OFF Test for infinite resistance between the B+ circuit and ground. If less than infinite resistance, repair the short to ground on the circuit. If infinite resistance, replace the blower motor control module. If the test lamp illuminates
5. Connect a DMM between the control circuit terminal 3 and ground.
6. Verify the resistance value is between.1 Mohms and 3.3 Mohms and there is a noticeable change when moving between the commanded fan speeds. If not between.1 Mohms and 3.3 Mohms or there is no noticeable change Ignition OFF, disconnect the X3 harness connector at the HVAC control module, Ignition ON. Test for less than 1 V between the control circuit and ground. If 1 V or greater, repair the short to voltage on the circuit. If less than 1 V Ignition OFF Test for infinite resistance between the control circuit and ground. If less than infinite resistance, repair the short to ground on the circuit. If infinite resistance Test for less than 2 ohms in the control circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, replace the HVAC control module. If between.1 Mohms and 3.3 Mohms and there is a noticeable change
7. Ignition OFF, connect the X2 harness connector at the blower motor control module, and disconnect the harness connector at the blower motor, ignition ON and blower ON.
8. Verify a test lamp illuminates between the B+ circuit terminal A and ground. If the test lamp does not illuminate Test for infinite resistance between the B+ circuit and ground. If less than infinite resistance, repair the short to ground on the circuit. If infinite resistance Test for less than 2 ohms in the B+ circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, replace the blower motor control module. If the test lamp illuminates
9. Connect a test lamp between the control circuit terminal B and the B+ circuit terminal A.
10. Verify the test lamp turns ON and OFF when moving the blower switch between the ON and OFF positions. If the test lamp is always OFF Test for less than 1 V between the control circuit and ground. If 1 V or greater, repair the short to voltage on the circuit. If less than 1 V Test for less than 2 ohms in the control circuit from end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, replace the blower motor control module. If the test lamp is always ON Test for infinite resistance between the control circuit and ground. If less than infinite resistance, repair the short to ground on the circuit. If infinite resistance, replace the blower motor control module. If the test lamp turns ON and OFF
11. Test or replace the blower motor.

Perform the Diagnostic Repair Verification after completing the repair.

1. «Blower Motor Control Module Replacement»(/gmc/sierra-2500/2012-2012/remont/automatic-hvac-system/#heating-ventilation-and-air-conditioning)
2. «Blower Motor Replacement»(/gmc/sierra-2500/2012-2012/remont/automatic-hvac-system/#heating-ventilation-and-air-conditioning)
3. «Control Module References»(/gmc/sierra-2500/2012-2012/remont/communication-devices/#programming-and-setup-all-systems__control-module-references) for ECM, and HVAC control module setup, programming, and setup

1. Perform the «Diagnostic System Check - Vehicle»(/gmc/sierra-2500/2012-2012/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures) prior to using this diagnostic procedure.
2. Review «Strategy Based Diagnosis»(/gmc/sierra-2500/2012-2012/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»(/gmc/sierra-2500/2012-2012/remont/oem-general-information/#vehicle-diagnostic-information-diagnostic-information-and-procedures__diagnostic-procedure-instructions) provides an overview of each diagnostic category.

Schematic Reference

HVAC Schematics

Connector End View Reference

WIRING SYSTEMS AND POWER MANAGEMENT - COMPONENT CONNECTOR END VIEWS - INDEX

Description and Operation

1. «Air Delivery Description and Operation»(/gmc/sierra-2500/2012-2012/remont/automatic-hvac-system/#hvac-system-automatic__air-delivery-description-and-operation)
2. «Air Temperature Description and Operation»(/gmc/sierra-2500/2012-2012/remont/automatic-hvac-system/#hvac-system-automatic__air-temperature-description-and-operation)

Electrical Information Reference

1. «Circuit Testing»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__circuit-testing)
2. «Connector Repairs»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__connector-repairs)
3. «Testing for Intermittent Conditions and Poor Connections»(/gmc/sierra-2500/2012-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-diagnostic-information-and-procedures__testing-for-intermittent-conditions-and-poor)
4. «Wiring Repairs»(/gmc/sierra-2500/2012-2012/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

Note. Check for bulletins before proceeding.

1. Ignition ON, move the blower motor switch into each speed position one at a time.
2. Verify that the blower motor operates properly in all speeds. If the blower motor does not operate properly in all speeds Refer to «Blower Motor Malfunction»(/gmc/sierra-2500/2012-2012/remont/automatic-hvac-system/#hvac-system-automatic) If the blower motor does operate properly in all speeds
3. Using the scan tool observe the mode, temperature and recirculation door positions. Verify the scan tool HVAC actual and commanded door positions are within 4 counts of each other. If not within the specified range Refer to «DTC B0228, B0413, B0423, or B3779»(/gmc/sierra-2500/2012-2012/remont/automatic-hvac-system/#hvac-system-automatic) Circuit/System Testing below. If within the specified range
4. Engine ON, A/C ON, place the temperature control in the coldest position. Verify that the A/C compressor clutch engages. If the A/C compressor clutch does not engage Refer to «Air Conditioning Compressor Malfunction»(/gmc/sierra-2500/2012-2012/remont/automatic-hvac-system/#hvac-system-automatic) If the A/C compressor is engaged, but the air is insufficiently cooled Refer to «Air Conditioning (A/C) System Performance Test (Gas Engine with Electric Cooling Fan)»(/gmc/sierra-2500/2012-2012/remont/automatic-hvac-system/#heating-ventilation-and-air-conditioning__air-conditioning-ac-system-performance-test) , «Air Conditioning (A/C) System Performance Test (Diesel Engine)»(/gmc/sierra-2500/2012-2012/remont/automatic-hvac-system/#heating-ventilation-and-air-conditioning__air-conditioning-ac-system-performance-test) , «Air Conditioning (A/C) System Performance Test (HP2)»(/gmc/sierra-2500/2012-2012/remont/automatic-hvac-system/#heating-ventilation-and-air-conditioning) , «Air Conditioning (A/C) System Performance Test (Gas Engine with Engine Driven Fan)»(/gmc/sierra-2500/2012-2012/remont/automatic-hvac-system/#heating-ventilation-and-air-conditioning__air-conditioning-ac-system-performance-test) If the A/C compressor clutch is engaged and the air is sufficiently cooled
5. Turn the A/C OFF and place the temperature control in the warmest position. If the air is insufficiently heated Refer to «Heating Performance Diagnostic»(/gmc/sierra-2500/2012-2012/remont/automatic-hvac-system/#heating-ventilation-and-air-conditioning__heating-performance-diagnostic) If the air is sufficiently heated
6. Engine OFF, ignition ON, cover the sunload sensor assembly with a shop towel or other suitable item.
7. Verify the scan tool Right Sunload Sensor and Left Sunload Sensor parameters are within 3 counts of each other. If not within the specified range Refer to «DTC B0183 or B0188»(/gmc/sierra-2500/2012-2012/remont/automatic-hvac-system/#hvac-system-automatic) If within the specified range
8. Measure actual outside air temperature and actual temperature at each air outlet duct using a thermometer.
9. Verify the scan tool Outside Air Temp. Raw and each Duct Actual parameter is within 5 degrees of the thermometer reading. If any are not within the specified range Refer to «DTC B0158, B0163, B0173, B0178, B0509, or B0514»(/gmc/sierra-2500/2012-2012/remont/automatic-hvac-system/#hvac-system-automatic) If all are within the specified range
10. Measure actual inside air temperature using a thermometer.
11. Verify the scan tool Inside Air Temp. Sensor is within 5 degrees of the thermometer reading. If not within the specified range Refer to Inside Air Temperature Sensor Circuit Malfunction below. If within the specified range
12. Ignition ON, observe the scan tool A/C Evaporator Temperature Sensor Raw parameter.
13. Verify the reading is between -35°C (-39°F) and 98°C (208°F) and changes with evaporator air temperature changes. If not within the specified range Refer to «DTC B3933»(/gmc/sierra-2500/2012-2012/remont/automatic-hvac-system/#hvac-system-automatic) If within the specified range
14. All OK

Inside Air Temperature Sensor Circuit Malfunction

1. Ignition OFF, disconnect the harness connector at the inside air temperature sensor.
2. Test for less than 10 ohms between the ground circuit terminal C and ground. If 10 ohms or greater Test for less than 2 ohms in the ground circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, repair the open/high resistance in the ground connection. If less than 10 ohms
3. Ignition ON
4. Verify a test lamp illuminates between the control circuit terminal B and ground. If the test lamp does not illuminate Ignition OFF Test for infinite resistance between the control circuit and ground. If less than infinite resistance, repair the short to ground on the circuit. If infinite resistance Test for less than 2 ohms in the control circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, replace the HVAC control module. If the test lamp does illuminate
5. Ignition OFF
6. Test for less than 10 ohms between the low reference circuit terminal D and ground. If 10 ohms or greater Test for less than 2 ohms in the low reference circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, replace the HVAC control module. If less than 10 ohms
7. Ignition ON
8. Verify the scan tool Inside Air Temp Sensor parameter is less than -35°C (-39°F). If -35°C (-39°F) or greater Ignition OFF, disconnect the X1 harness connector at the HVAC control module. Test for infinite resistance between the signal circuit terminal A and ground. If less than infinite resistance, repair the short to ground on the circuit. If infinite resistance, replace the HVAC control module. If less than -35°C (-39°F)
9. Install a 3-amp fused jumper wire between the signal circuit terminal A and the low reference circuit terminal B.
10. Verify the scan tool Inside Air Temp Sensor parameter is greater than 85°C (185°F). If 85°C (185°F) or less Disconnect the X1 harness connector at the HVAC control module. Test for less than 1 V between the signal circuit and ground. If 1 V or greater, repair the short to voltage on the circuit. If less than 1 V Ignition OFF Test for less than 2 ohms in the signal circuit end to end. If 2 ohms or greater, repair the open/high resistance in the circuit. If less than 2 ohms, replace the HVAC control module. If greater than 85°C (185°F)
11. Replace the inside air temperature sensor.

1. Ignition OFF, disconnect the harness connector at the appropriate temperature sensor.
2. Measure the resistance between the signal terminal A or 1 and the low reference terminal B or 2.
3. Verify the resistance is within 5% of the readings contained in the «Sensor Resistance Table»(/gmc/sierra-2500/2012-2012/remont/automatic-hvac-system/#hvac-system-automatic__sensor-resistance-table) . If not within 5% Replace the appropriate sensor If within 5%
4. All OK.

Perform the Diagnostic Repair Verification after completing the repair.

1. «Duct Air Temperature Sensor Replacement - Lower Left Side»(/gmc/sierra-2500/2012-2012/remont/automatic-hvac-system/#hvac-system-automatic)
2. «Duct Air Temperature Sensor Replacement - Lower Right Side»(/gmc/sierra-2500/2012-2012/remont/automatic-hvac-system/#hvac-system-automatic)
3. «Duct Air Temperature Sensor Replacement - Upper Left Side»(/gmc/sierra-2500/2012-2012/remont/automatic-hvac-system/#hvac-system-automatic)
4. «Duct Air Temperature Sensor Replacement - Lower Left Side»(/gmc/sierra-2500/2012-2012/remont/automatic-hvac-system/#hvac-system-automatic)
5. «Air Conditioning Refrigerant Temperature Sensor Replacement»(/gmc/sierra-2500/2012-2012/remont/automatic-hvac-system/#hvac-system-automatic)
6. «Ambient Air Temperature Sensor Replacement»(/gmc/sierra-2500/2012-2012/remont/automatic-hvac-system/#hvac-system-automatic)
7. «Ambient Light Sensor Replacement»(/gmc/sierra-2500/2012-2012/remont/exterior-lights/#lighting-system)
8. «Control Module References»(/gmc/sierra-2500/2012-2012/remont/communication-devices/#programming-and-setup-all-systems__control-module-references) for control module replacement, programming and setup

Afterblow Enabling

The afterblow mode can be enabled using the scan tool. The afterblow mode allows the blower motor to operate after the engine has been turned off. This operation of the blower motor dries the evaporator core, which reduces the amount of microbial growth which can create undesirable odors.

Use the following procedure in order to enable the afterblow mode

1. Connect the Scan Tool.
2. Turn ON the ignition, with the engine OFF.
3. Build the vehicle with the scan tool.
4. Select HVAC Control Module
5. Select Module Setup.
6. Select Afterblow Option.
7. Upon selecting the afterblow option a asterix will appear next to the word afterblow meaning the function is enabled.
8. Select the save option in the lower left of the screen.

When afterblow has been enabled by the scan tool the blower motor will operate at 68 percent blower speed for 2 minutes 30 seconds to 4 minutes after the engine has been in Key OFF for 30 minutes.

The following conditions must be met for the HVAC module to operate the afterblow

1. The outside air temperature must be at least 21°C (70°F).
2. The A/C compressor must have operated during the latest key cycle.
3. The engine must be turned off for at least 30 minutes.
4. The system voltage must be at least 12 volts.

Actuator Recalibration

When replacing the HVAC control module it will be necessary to allow the HVAC control module to perform a calibration process. When installing the HVAC control module be sure to perform the following

1. Place the ignition switch to the OFF position.
2. Disconnect the scan tool.
3. Install the HVAC control module.
4. Connect all previously disconnected components.
5. Start the vehicle.
6. Wait 40 seconds for the HVAC control module to self-calibrate.
7. Verify that no DTCs have set as current DTCs.

When replacing the HVAC actuator it will be necessary to allow the HVAC control module to perform a calibration process. When installing the HVAC actuator be sure to perform one of the following

Preferred Method (w/Scan Tool)

1. Clear all DTCs.
2. Place the ignition switch in the OFF position.
3. Install the HVAC actuator.
4. Connect all previously disconnected components.
5. Start the vehicle.
6. With the scan tool, initiate the Motor Re-calibration feature of the Heating and Air Conditioning Special Functions menu.
7. Verify that no DTCs have set as current DTCs.

Alternate Method (w/o Scan Tool)

1. Clear all DTCs.
2. Place the ignition switch to the OFF position.
3. Install the HVAC actuator.
4. Connect all previously disconnected components.
5. Remove the HVAC/ECAS fuse for a minimum of 10 seconds.
6. Install the HVAC/ECAS fuse.
7. Start the vehicle.
8. Wait 40 seconds for the HVAC control module to self-calibrate.
9. Verify that no DTCs have set as current DTCs.

Scheme 46

HVAC Control Module Replacement

Scheme 47

Air Inlet Valve Actuator Replacement

Scheme 48

Mode Valve Actuator Replacement

Scheme 49

Temperature Valve Actuator Replacement - Right Side

Scheme 50

Temperature Valve Actuator Replacement - Left Side

Removal Procedure

1. Remove the instrument panel compartment door assembly. Refer to «Instrument Panel Compartment Door Replacement (With RPO SLT)»(/gmc/sierra-2500/2012-2012/remont/exteriorinterior-trim/#instrument-panel-trim-and-console-trim) .
2. Remove the instrument panel inflatable restraint module. Refer to «Instrument Panel Inflatable Restraint Module Replacement (Without SLT)»(/gmc/sierra-2500/2012-2012/remont/airbag/#supplemental-inflatable-restraint-system) , «Instrument Panel Inflatable Restraint Module Replacement (With SLT)»(/gmc/sierra-2500/2012-2012/remont/airbag/#supplemental-inflatable-restraint-system) .
3. Disconnect the air conditioning refrigerant temperature sensor connector (1).
4. Test the resistance reading of the air conditioning refrigerant temperature sensor. Refer to «Sensor Resistance Table»(/gmc/sierra-2500/2012-2012/remont/automatic-hvac-system/#hvac-system-automatic__sensor-resistance-table) .
5. Remove the right side instrument panel insulator. Refer to «Instrument Panel Insulator Replacement (With RPO SLT)»(/gmc/sierra-2500/2012-2012/remont/exteriorinterior-trim/#instrument-panel-trim-and-console-trim) , «Instrument Panel Insulator Replacement (Without RPO SLT)»(/gmc/sierra-2500/2012-2012/remont/exteriorinterior-trim/#instrument-panel-trim-and-console-trim)
6. Remove the rubber plug from the bottom of the air conditioning and heater module assembly if equipped, and proceed to step 13. If air conditioning and heater module assembly is not equipped with rubber plug proceed to the next step.
7. Open the template by clicking on the magnifying glass.
8. Above the template image, click on the printer icon next to the 1:1 in order to print in the correct scale. NOTE: No other printing method is acceptable as scale changes print size.
9. Make a copy of the template using a copy machine, and re-size the template vertical and horizontal axis to a scale 50 mm.
10. Cut the template out along the printed ribs.
11. Secure the template to the bottom of the air conditioning and heater module assembly (1) with tape. The template should fit snugly between the molded ribs.
12. Slowly drill a hole through the air conditioning and heater module assembly using a 1-1/4 inch (32 mm) hole saw following the template outline.
13. Inspect the air conditioning refrigerant temperature sensor through the newly drilled hole. The air conditioning refrigerant temperature sensor should be secure to the center of the evaporator core.
14. If the air conditioning refrigerant temperature sensor (1) is not secured to the evaporator core (2), use a pair of long needle nose pliers to grip the air conditioning refrigerant temperature sensor at the plastic base, and insert air conditioning refrigerant temperature sensor into the evaporator core.
15. Perform the air conditioning refrigerant temperature sensor calibration check using the scan tool.
16. If it is determine that the air conditioning refrigerant temperature sensor is defective and needs to be replaced, use a pair of long needle nose pliers to grip the air conditioning refrigerant temperature sensor at the plastic base. Pull the air conditioning refrigerant temperature sensor out away from the evaporator core and out of the newly drilled hole.
17. Secure 1 wire, 30 inches (762 mm) in length to the air conditioning refrigerant temperature sensor side of the sensor.
18. Secure 1 wire, 30 inches (762 mm) in length to the air conditioning refrigerant temperature sensor connector side of the sensor.
19. Remove the air conditioning refrigerant temperature sensor harness grommet (1) from the top of the air conditioning and heater module assembly (2).
20. Pull the air conditioning refrigerant temperature sensor (1) up and out of the air conditioning and heater module assembly (2), leaving part of the secured wire exiting the newly drilled hole.

Installation Procedure

1. Secure the new air conditioning refrigerant temperature sensor to the wire that was secured to the air conditioning refrigerant temperature sensor side.
2. Pull the wire exiting the newly drilled hole, routing the air conditioning refrigerant temperature sensor (1) back into the air conditioning and heater module assembly (2).
3. Install the air conditioning refrigerant temperature sensor harness grommet (1) back into the top of the air conditioning and heater module assembly (2).
4. Connect the air conditioning refrigerant temperature sensor connector (1).
5. Use a pair of long needle nose pliers to grip the air conditioning refrigerant temperature sensor at the plastic base (1), and insert air conditioning refrigerant temperature sensor into the center of the evaporator core (2).
6. Perform the air conditioning refrigerant temperature sensor calibration check using the scan tool.
7. Install 1 1/4 (32 mm) inch plug (P/N 94535734) into the newly drilled hole.
8. Apply silicon sealer (GM#88861417) around the perimeter of the plug.
9. Install the right side instrument panel insulator. Refer to «Instrument Panel Insulator Replacement (With RPO SLT)»(/gmc/sierra-2500/2012-2012/remont/exteriorinterior-trim/#instrument-panel-trim-and-console-trim) , «Instrument Panel Insulator Replacement (Without RPO SLT)»(/gmc/sierra-2500/2012-2012/remont/exteriorinterior-trim/#instrument-panel-trim-and-console-trim)
10. Install the instrument panel inflatable restraint module. Refer to «Instrument Panel Inflatable Restraint Module Replacement (Without SLT)»(/gmc/sierra-2500/2012-2012/remont/airbag/#supplemental-inflatable-restraint-system) , «Instrument Panel Inflatable Restraint Module Replacement (With SLT)»(/gmc/sierra-2500/2012-2012/remont/airbag/#supplemental-inflatable-restraint-system) .
11. Install the instrument panel compartment door assembly. Refer to «Instrument Panel Compartment Door Replacement (With RPO SLT)»(/gmc/sierra-2500/2012-2012/remont/exteriorinterior-trim/#instrument-panel-trim-and-console-trim) .

Scheme 51

Duct Air Temperature Sensor Replacement - Upper Right Side

Scheme 52

Duct Air Temperature Sensor Replacement - Upper Left Side

Scheme 53

Duct Air Temperature Sensor Replacement - Lower Left Side

Scheme 54

Duct Air Temperature Sensor Replacement - Lower Right Side

Scheme 55

Ambient Air Temperature Sensor Replacement

1. Remove the left windshield garnish molding. Refer to «Windshield Pillar Garnish Molding Replacement»(/gmc/sierra-2500/2012-2012/remont/exteriorinterior-trim/#interior-trim-and-interior-paneling) .
2. Remove the left center pillar assist handle. Refer to «Roof Rail Rear Assist Handle Replacement»(/gmc/sierra-2500/2012-2012/remont/exteriorinterior-trim/#interior-trim-and-interior-paneling) .
3. Remove the center pillar garnish molding. Refer to «Center Pillar Upper Garnish Molding Replacement»(/gmc/sierra-2500/2012-2012/remont/exteriorinterior-trim/#interior-trim-and-interior-paneling) .
4. Remove the left sunshade. Refer to «Sunshade Replacement»(/gmc/sierra-2500/2012-2012/remont/exteriorinterior-trim/#interior-trim-and-interior-paneling) .
5. Gently pull down the headliner.
6. Disconnect the electrical connector from the inside air temperature sensor.
7. Partially remove the inside air temperature sensor from the headliner.
8. Remove the sensor grille from the inside air temperature sensor.
9. Remove the inside air temperature sensor from the headliner.

1. Install the new sensor grille to the headliner.
2. Install the inside air temperature sensor to the headliner and sensor grille.
3. Connect the electrical connector to the inside air temperature sensor.
4. Install the left sunshade. Refer to «Sunshade Replacement»(/gmc/sierra-2500/2012-2012/remont/exteriorinterior-trim/#interior-trim-and-interior-paneling) .
5. Install the left center pillar garnish molding. Refer to «Center Pillar Upper Garnish Molding Replacement»(/gmc/sierra-2500/2012-2012/remont/exteriorinterior-trim/#interior-trim-and-interior-paneling) .
6. Install the left center assist handle. Refer to «Roof Rail Rear Assist Handle Replacement»(/gmc/sierra-2500/2012-2012/remont/exteriorinterior-trim/#interior-trim-and-interior-paneling) .
7. Install the left windshield garnish molding. Refer to «Windshield Pillar Garnish Molding Replacement»(/gmc/sierra-2500/2012-2012/remont/exteriorinterior-trim/#interior-trim-and-interior-paneling) .

Scheme 56

Sun Load Temperature Sensor Replacement

Air Delivery Description and Operation

The air delivery description and operation is divided into 7 areas

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

HVAC Control Components

HVAC Control Module

The HVAC control module is a GMLAN device that interfaces between the operator and the HVAC system to maintain air temperature and distribution settings. The battery positive voltage circuit provides power that the control module uses for keep alive memory (KAM). If the battery positive voltage circuit loses power, all HVAC DTCs and settings will be erased from KAM. The body control module (BCM), which is the vehicle mode master, provides a device on signal. The control module supports the following features

Auxiliary HVAC Control Module

The auxiliary HVAC control module is a GMLAN device that receives analog Inputs from the front HVAC control assembly and GMLAN message inputs from the rear seat audio (RSA) control module to maintain auxiliary air temperature and auxiliary air distribution settings. The battery positive voltage circuit provides power that the control module uses for KAM. If the battery positive voltage circuit loses power, all auxiliary HVAC DTCs and settings will be erased from KAM. The auxiliary HVAC control module will perform a recalibration of the electric actuators when commanded with a scan tool or if KAM is lost. This will ensure the actuators are moving with in the calibrated range.

RSA Control Module

The RSA Control Module is a GMLAN device that interfaces between the rear seat passengers and the auxiliary HVAC control module. The battery positive voltage circuit provides power that the control module uses for KAM. Air temperature, blower motor and air delivery rocker type switches are located on the face of the module.

These switches enable the module to send a GMLAN serial data message to the auxiliary HVAC control module for the change request. The module does not store auxiliary HVAC DTCs.

Mode Actuator

The mode actuator is a 5-wire bi-directional electric motor that incorporates a feedback potentiometer. Ignition 3 voltage, low reference, control, 5-volt reference and position signal circuits enable the actuator to operate. The control circuit uses either a 0, 2.5 or 5-volt signal to command the actuator movement. When the actuator is at rest, the control circuit value is 2.5 volts. A 0 or 5-volt control signal commands the actuator movement in opposite directions. When the actuator shaft rotates, the potentiometers adjustable contact changes the door position signal between 0-5 volts.

The HVAC control module uses a range of 0-255 counts to index the actuator position. The door position signal voltage is converted to a 0-255 count range. When the module sets a commanded, or targeted, value, the control signal is changed to either 0 or 5 volts depending upon the direction that the actuator needs to rotate to reach the commanded value. As the actuator shaft rotates the changing position signal is sent to the module. Once the position signal and the commanded value are the same, the module changes the control signal to 2.5 volts.

Auxiliary Mode Actuator

The auxiliary mode actuator is a 5-wire bi-directional electric motor that incorporates a feedback potentiometer. Ignition 3 voltage, low reference, control, 5-volt reference and position signal circuits enable the actuator to operate. The control circuit uses either a 0, 2.5 or 5-volt signal to command the actuator movement. When the actuator is at rest, the control circuit value is 2.5 volts. A 0 or 5-volt control signal commands the actuator movement in opposite directions. When the actuator shaft rotates, the potentiometers adjustable contact changes the door position signal between 0-5 volts.

The auxiliary HVAC control module uses a range of 0-255 counts to index the actuator position. The door position signal voltage is converted to a 0-255 count range. When the module sets a commanded, or targeted, value, the control signal is changed to either 0 or 5 volts depending upon the direction that the actuator needs to rotate to reach the commanded value. As the actuator shaft rotates the changing position signal is sent to the module.

Once the position signal and the commanded value are the same, the module changes the control signal to 2.5 volts.

Blower Motor Control Processor

The blower motor control module is an interface between the HVAC control module and the blower motor. The blower motor speed control, battery positive and ground circuits enable the control module to operate. The HVAC control module provides a variable voltage to the blower motor control module to request the selected blower speed. The blower motor control module provides a pulse width modulation (PWM) signal to the blower motor in order to control the blower motor speed. The module supplies 12 volts to the blower motor through the blower motor voltage supply circuit.

Auxiliary Blower Motor Control Processor

The auxiliary blower motor control processor controls the speed of the blower motor by increasing or decreasing the voltage drop on the ground side of the auxiliary blower motor. The auxiliary HVAC control module or rear seat audio module (RSA) provides a voltage signal to the auxiliary blower motor control processor over the auxiliary blower motor speed control circuit. As the requested blower speed increases, the auxiliary HVAC control module or rear seat audio module (RSA) increases the amount of time that the speed signal is modulated to ground. As the requested blower speed decreases, the auxiliary HVAC control module or rear seat audio module (RSA) decreases the amount of time that the signal is modulated to ground.

Air Speed - Front Control

The blower control switch is integrated into the HVAC control module. The 2 rocker type switches provide the vehicle operator the ability to select several blower speeds. The HVAC control module uses a bar graph type display to indicate the selected blower speed. The blower motor control module is an interface between the HVAC control module and the blower motor. The blower motor speed control, battery positive and ground circuits enable the control module to operate. The HVAC control module provides a variable voltage to the blower motor control module to request the selected blower speed. The blower motor control module provides a pulse width modulation (PWM) signal to the blower motor in order to control the blower motor speed. The module supplies 12 volts to the blower motor through the blower motor voltage supply circuit. When the HVAC control module is operating in AUTO mode, the system automatically controls the blower speed. If an OnStar® call is initiated while the blower is in the high speed position the blower speed will be lowered to reduce background noise.

Air Speed - Auxiliary

A rocker type switch on the RSA control module provides the operator the ability to select several blower speeds. The RSA control module uses a bar graph to indicate the selected blower speed. The auxiliary blower motor control processor supplies a 5-volt reference to the auxiliary HVAC control module on the auxiliary blower motor speed control circuit. The auxiliary HVAC control module pulls the 5-volt reference low towards ground to provide a blower motor speed signal. As the voltage decreases the blower speed increases. Power and ground are provided to the auxiliary blower motor control processor through the battery positive voltage and ground circuits. The auxiliary HVAC control module can not request A/C operation from the powertrain control module (PCM).

Air Distribution

The HVAC control module controls the distribution of air by the use of a mode actuator. The modes that may be selected are

1. Defrost
2. Defog
3. Panel
4. Bi-Level
5. Floor

The mode actuator is connected to the mode door by a cam type linkage system. Depending on the position of the door, air is directed through the HVAC module and distributed through various ducts leading to the outlets in the dash. If the HVAC control module detects a fault with the mode door the HVAC control module will try to drive the actuator for a predetermined amount of time, to defrost, which is the defaulted position for the mode door actuator. When the mode switch is placed in the defrost or defog positions the A/C is commanded on and the recirculation door is moved to the outside air position to help reduce window fogging. A/C is available in all modes and recirculation is only available in the panel and bi-level modes.

Mode Actuator

The mode actuator is an electronic stepper motor with feedback potentiometers. The HVAC control module sends signals to the mode door actuator through the mode door control circuit. Zero volts drive the actuator in one direction while 5 volts move the actuator in the opposite direction. When the actuator receives 2.5 volts, the actuator rotation stops. A 5-volt reference signal is sent out over the 5-volt reference circuit to the mode actuator. When you select a desired mode setting, logic determines the value of the mode actuator signals. The HVAC control modules software uses this reference voltage in order to determine the position of the mode actuator through the mode door position signal circuit. The motor moves the mode door to the desired position.

Front Defrost

When defrost is selected, the A/C compressor is activated. The A/C compressor clutch will engage when ambient temperatures are above 3°C (38 F). The blower motor will be activated, regardless of the coolant temperature. The HVAC control module will override the auxiliary HVAC control module so a high volume of air is delivered to the front defrost vents. The rear window defogger does not affect the HVAC system.

Air Distribution - Auxiliary Control

The auxiliary HVAC system provides ventilation for the rear seat occupants. The rear seat occupants will exercise control of the auxiliary air delivery modes, air speed and air temperature setting.

When the auxiliary mode switch is toggled, a signal is sent to the auxiliary mode actuator through the auxiliary mode door control circuit. Power and ground are supplied to the auxiliary mode actuator through the ignition 3 voltage and ground circuits.

A rocker type switch on the RSA control module provides the operator the ability to select several blower speeds. The RSA control module uses a bar graph to indicate the selected blower speed.

Recirculation Operation

The HVAC control module controls the air intake through the recirculation actuator. The recirculation switch closes the recirculation door in order to circulate the air within the vehicle. The outside air switch opens the recirculation door in order to route outside air into the vehicle. Regardless of the blower motor switch position, recirculation is available only in the panel and bi-level mode switch positions. Including the OFF position. The mode switch must be placed in either the panel or bi-level position before the blower motor switch is placed in the OFF position. In order to reduce windshield fogging, outside air is circulated when the mode switch is in the defrost or defog positions. If the recirculation switch is pressed into the ON position when the mode switch is in an unavailable mode position, then the recirculation switch LED will flash 3 times. If the HVAC control module detects a fault with the recirc door the HVAC control module will try to drive the actuator for a predetermined amount of time, to outside air, which is the defaulted position for the recirculation actuator.

Automatic Operation

In automatic operation, the HVAC control module will maintain the comfort level inside of the vehicle by controlling the A/C compressor clutch, the blower motor, the air temperature actuators, mode actuator and circulation.

To place the HVAC system in Automatic mode, the following is required

1. The Auto switch must be activated
2. The air temperature switch must be in any other position other than full hot or full cold position

Once the desired temperature is reached, the blower motor, mode, recirculation and temperature actuators will automatically be adjusted to maintain the temperature selected. The HVAC control module performs the following functions to maintain the desired air temperature

Monitor the following sensors

1. Inside Air Temperature Sensor
2. Ambient Air Temperature Sensor
3. Lower Left Air Temperature Sensor
4. Lower Right Air Temperature Sensor
5. Upper Left Air Temperature Sensor
6. Upper Right Air Temperature Sensor Regulate blower motor speed Position the air temperature actuator Position the mode actuator Position the recirculation actuator Request A/C operation

Remote Start

Remote Start Activation

The following describes the HVAC control head functionality upon receiving the remote start active serial data message and a power mode status is set to off/awake. The outside air temperature (OAT) sensor on automatic systems, is utilized to determine the moding of the following features: Blower Mode, Bi-level, Floor, Defrost, Recirc and Rear Defrost. Calibratable temperatures are utilized to provide low, mid and high temperature ranges for the selectable feature. Blower and mode have the range to select any valid feature positions. When the remote start active serial data is received, ignition-OFF loop HVAC algorithms will act the same as if a run power mode was received, i.e. re-calibration, afterblow, ignition-OFF motor positioning etc. The OFF timer and the ignition ON timer have the functionality as in the Run mode.

The remote start system operates in one of three zones of operation

1. Cold ambient temperature that is below 5°C (41°F)
2. Hot ambient temperature that is above 30°C (86°F)
3. Mid ambient temperature that is anything between the cold and hot values

1. In cold ambient, the system uses 74°F setpoint, auto blower, defrost mode, rear defrost and/or heated mirrors on, heated seats on, rear in mimic.
2. In mid ambient, the system uses 74°F setpoint, auto blower, auto mode, rear in mimic.
3. In hot ambient, the system uses 74°F setpoint (60°F setpoint in 2008), auto blower, auto mode, rear in mimic.

Remote Start De-activation

When the remote start is exited, GMLAN power mode equals run mode or remote start engine. In the case of automatic settings, the displays will revert to the actual state of operation of the features, on the basis of their normal control algorithms.

Air Temperature Description and Operation

The air temperature controls are divided into 7 areas

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

The HVAC control module is a GMLAN device that interfaces between the operator and the HVAC system to maintain air temperature and distribution settings. The battery positive voltage circuit provides power that the control module uses for keep alive memory (KAM). If the battery positive voltage circuit loses power, all HVAC DTCs and settings will be erased from KAM. The body control module (BCM), which is the vehicle mode master, provides a device on signal. The control module supports the following features

Auxiliary HVAC Control Module

The auxiliary HVAC control module is a GMLAN device that receives analog inputs from the front HVAC control assembly and GMLAN message inputs from the rear seat audio control module to maintain auxiliary air temperature and auxiliary air distribution settings. The battery positive voltage circuit provides power that the control module uses for KAM. If the battery positive voltage circuit loses power, all auxiliary HVAC DTCs and settings will be erased from KAM. The auxiliary HVAC control module will perform a recalibration of the electric actuators when commanded with a scan tool or if KAM is lost. This will ensure the actuators are moving with in the calibrated range.

Rear Seat Audio Control Module

The rear seat audio control module is a GMLAN device that interfaces between the rear seat passengers and the auxiliary HVAC control module. The battery positive voltage circuit provides power that the control module uses for KAM. Air temperature, blower motor and air delivery rocker type switches are located on the face of the module. Pressing a switch enables the module to send a GMLAN serial data message to the auxiliary HVAC control module for the change request. The module does not store auxiliary HVAC DTCs.

Air Temperature Actuator

The air temperature actuators are a 5-wire bi-directional electric motor that incorporates a feedback potentiometer. Ignition 3 voltage, low reference, control, 5-volt reference and position signal circuits enable the actuator to operate. The control circuit uses either a 0, 2.5 or 5 volt signal to command the actuator movement. When the actuator is at rest, the control circuit value is 2.5 volts. A 0 or 5-volt control signal commands the actuator movement in opposite directions. When the actuator shaft rotates, the potentiometers adjustable contact changes the door position signal between 0-5 volts.

The HVAC control module uses a range of 0-255 counts to index the actuator position. The door position signal voltage is converted to a 0-255 count range. When the module sets a commanded, or targeted, value, the control signal is changed to either 0 or 5 volts depending upon the direction that the actuator needs to rotate to reach the commanded value. As the actuator shaft rotates the changing position signal is sent to the module. Once the position signal and the commanded value are the same, the module changes the control signal to 2.5 volts.

Auxiliary Air Temperature Actuator

The auxiliary air temperature actuator is a 5-wire bi-directional electric motor that incorporates a feedback potentiometer. Ignition 3 voltage, low reference, control, 5-volt reference and position signal circuits enable the actuator to operate. The control circuit uses either a 0, 2.5 or 5-volt signal to command the actuator movement. When the actuator is at rest, the control circuit value is 2.5 volts. A 0 or 5-volt control signal commands the actuator movement in opposite directions. When the actuator shaft rotates, the potentiometers adjustable contact changes the door position signal between 0-5 volts. The auxiliary HVAC control module uses a range of 0-255 counts to index the actuator position. The door position signal voltage is converted to a 0-255 count range. When the module sets a commanded, or targeted, value, the control signal is changed to either 0 or 5 volts depending upon the direction that the actuator needs to rotate to reach the commanded value. As the actuator shaft rotates the changing position signal is sent to the module. Once the position signal and the commanded value are the same, the module changes the control signal to 2.5 volts.

Air Temperature Sensor

The air temperature sensors are a 2-wire negative temperature co-efficient thermistor. The vehicle uses the following air temperature sensors

1. Ambient Air Temperature Sensor
2. Inside Air Temperature Sensor Assembly
3. Upper Left Air Temperature Sensor
4. Upper Right Air Temperature Sensor
5. Lower Left Air Temperature Sensor
6. Lower Right Air Temperature Sensor
7. Upper Air Temperature Sensor - Auxiliary
8. Lower Air Temperature Sensor - Auxiliary

A signal and low reference circuit enables the sensor to operate. As the air temperature surrounding the sensor increases, the sensor resistance decreases. The sensor signal voltage decreases as the resistance decreases. The sensor operates within a temperature range between -40 to +101°C (-40 to +215°F). The sensor signal varies between 0-5 volts.

The input of the duct air temperature sensors are different from the ambient and inside air temperature sensors. The HVAC control module converts the signal to a range between 0-255 counts. As the air temperature increases the count value will decrease. If the HVAC control module or auxiliary HVAC control module detects a malfunctioning sensor, then the control module software will use a defaulted air temperature value. The default value for the ambient and inside air temperature sensors will be displayed on the scan tool. The default value for the duct air temperature sensors will not be displayed on the scan tool. The scan tool parameter for the duct air temperature sensors are the actual state of the signal circuit. The default action ensures that the HVAC system can adjust the inside air temperature near the desired temperature until the condition is corrected.

The ambient air temperature sensor mounts underhood and can be affected by city traffic, by idling, and by restarting a hot engine. Therefore, the HVAC control module filters the value of the ambient air temperature sensor for temperature display. The ambient air temperature value is updated under the following conditions

The scan tool has the ability to update the displayed ambient air temperature. To update the ambient air temperature display on the HVAC control module, perform the following procedure: Turn ON the ignition. Simultaneously press the A/C and Recirc switches for 5 seconds.

Evaporator Temperature Sensor

The evaporator temperature sensor is a 2-wire negative temperature co-efficient thermistor. The sensor operates within a temperature range of -40 to +85°C (-40 to +185°F). The sensor is installed at the evaporator and measures its temperature. If the temperature drops under 3°C (38°F), the compressor will be switched off in order to prevent a frozen evaporator.

Sunload Sensor Assembly

The sunload sensor is a 2-wire photo diode. The vehicle uses left and right sunload sensors. The 2 sensors are integrated into the sunload sensor assembly. Low reference and signal circuits enable the sensor to operate. As the light shining upon the sensor gets brighter, the sensor resistance increases. The sensor signal decreases as the resistance increases. The sensor operates within an intensity range between completely dark and bright. The sensor signal varies between 0-5 volts. The HVAC control module converts the signal to a range between 0-255 counts. The sunload sensor provides the HVAC control module a measurement of the amount of light shining on the vehicle. Bright, or high intensity, light causes the vehicles inside temperature to increase. The HVAC system compensates for the increased temperature by diverting additional cool air into the vehicle. If the HVAC control module detects a malfunctioning sensor, then the control module software will use a defaulted sunload value. This value will not be displayed on the scan tool. The default action ensures that the HVAC system can adjust the inside air temperature near the desired temperature until the condition is fixed. The scan tool parameter for the sunload sensor is the actual state of the signal circuit.

A/C Refrigerant Pressure Sensor

The A/C refrigerant pressure sensor is a 3-wire piezoelectric pressure transducer. A 5-volt reference, low reference, and signal circuits enable the sensor to operate. The A/C pressure signal can be between 0-5 volts. When the A/C refrigerant pressure is low, the signal value is near 0 volts. When the A/C refrigerant pressure is high, the signal value is near 5 volts. The powertrain control module (PCM) converts the voltage signal to a pressure value.

The A/C refrigerant pressure sensor protects the A/C system from operating when an excessively high pressure condition exists. The PCM disables the compressor clutch if the A/C pressure is more than 2957 kPa (429 psi). The clutch will be enabled after the pressure decreases to less than 1578 kPa (229 psi).

The A/C low pressure switch protects the A/C system from a low pressure condition that could damage the A/C compressor or cause evaporator icing. The HVAC control module applies 12 volts to the A/C low pressure switch signal circuit. The switch will open when the A/C low side pressure reaches 151 kPa (22 psi). This prevents the A/C compressor from operating. The switch will then close when A/C low pressure side reaches 275 kPa (40 psi). This enables the A/C compressor to turn back ON.

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. The vehicle passenger can offset the passenger temperature as much as 16.7°C (30°F). Regardless of the temperature setting, the following can affect the rate that the HVAC system can achieve the desired temperature

1. Recirculation actuator setting
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 control module makes the following actions when automatic operation is not selected, and an air temperature setting is selected

1. When the air temperature switch is placed in the warmest position, the control module commands the air temperature door to divert maximum air past the heater core.
2. When the air temperature switch is placed in the coldest position, the control module commands the air temperature door to direct air to bypass the heater core.

When the air temperature switch is placed between the warmest and coldest positions, the control module monitors the following sensor inputs to determine the air temperature door position that diverts the appropriate amount of air past the heater core in order to achieve the desired temperature

1. Sunload
2. Duct temperatures
3. Ambient temperature
4. Inside temperature

The A/C system can be engaged by either pressing the A/C switch or during automatic operation. The HVAC control module sends a GMLAN message to the powertrain control module (PCM) for A/C compressor engagement. The PCM will provide a ground for the A/C compressor relay enabling it to close its internal contacts to send battery voltage to the A/C compressor clutch coil. The A/C compressor diode will prevent a voltage spike, resulting from the collapse of the magnetic field of the coil, from entering the vehicle electrical system when the compressor is disengaged.

The following conditions must be met in order for the A/C compressor clutch to turn ON if they are not all met and an A/C request is made the LED on the A/C switch will flash

1. Ambient air temperature above 7°C (45°F)
2. A/C low pressure switch signal circuit is grounded
3. A/C refrigerant pressure sensor parameter is less than 2957 kPa (429 psi)
4. PCM receives an A/C request from the HVAC control module
5. Engine coolant temperature (ECT) is less than 121°C (250°F)
6. The engine RPM is more than 550 RPM
7. The throttle position is less than 100 percent

The HVAC control module monitors the A/C low pressure switch signal circuit. If the voltage signal on this circuit has no voltage drop the module will interpret this condition as a low pressure, disabling the A/C request. The A/C low pressure switch will open its internal contacts at 151 kPa (22 psi). Then close the contacts at 275 kPa (40 psi) to resume A/C operation. This switch assists in cycling the A/C compressor and prevents A/C compressor operation if system has a low refrigerant level.

The PCM monitors the A/C refrigerant pressure sensor signal circuit. The voltage signal on this circuit is proportional to the refrigerant pressure inside the A/C high side pressure line. As the pressure inside the line increases, so does the voltage signal. If the pressure is above 2957 kPa (429 psi), the A/C compressor output is disabled. When the pressure lowers to 1578 kPa (229 psi), the PCM enables the compressor to operate.

The sensor information is used by the PCM to determine the following

1. The A/C high side pressure
2. An A/C system load on the engine
3. An excessive A/C high side pressure
4. The heat load at the A/C condenser

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

1. Ambient air temperature is less than 7°C (45°F)
2. Throttle position is 100 percent
3. The A/C low pressure switch is open
4. A/C high side pressure is more than 2957 kPa (429 psi)
5. A/C low side pressure is less than 151 kPa (22 psi)
6. ECT is more than 121°C (250°F)
7. Engine speed is more than 5500 RPM
8. Transmission shift
9. PCM detects excessive torque load
10. PCM detects insufficient idle quality
11. PCM detects a hard launch condition

In automatic operation, the HVAC control module will maintain the comfort level inside of the vehicle by controlling the A/C compressor clutch, the blower motor, the air temperature actuators, mode actuator and recirculation.

To place the HVAC system in Automatic mode, the following is required

1. The Auto switch must be activated
2. The air temperature switch must be in any other position other than full hot or full cold position

Once the desired temperature is reached, the blower motor, mode, recirculation and temperature actuators will automatically be adjusted to maintain the temperature selected. The HVAC control module performs the following functions to maintain the desired air temperature

Monitor the following sensors

1. Inside Air Temperature Sensor
2. Ambient Air Temperature Sensor
3. Lower Left Air Temperature Sensor
4. Lower Right Air Temperature Sensor
5. Upper Left Air Temperature Sensor
6. Upper Right Air Temperature Sensor
7. Regulate blower motor speed.
8. Position the air temperature actuator.
9. Position the mode actuator.
10. Position the recirculation actuator.
11. Request A/C operation.

In automatic operation, the auxiliary HVAC control module will maintain the comfort level inside of the vehicle by controlling the auxiliary blower motor, the auxiliary air temperature actuator and the auxiliary mode actuator.

To place the auxiliary HVAC system in Automatic mode, the following is required

1. The auxiliary blower motor switch on the auxiliary HVAC control assembly must be in the Auto position.
2. The auxiliary mode switch on the auxiliary HVAC control assembly must be in the Auto position.
3. The auxiliary air temperature switch must be in any other position other than full hot or full cold position.

Once the desired temperature is reached, the auxiliary blower motor, auxiliary mode and auxiliary temperature actuator will automatically be adjusted to maintain the temperature selected. The auxiliary HVAC control module performs the following functions to maintain the desired air temperature

1. Upper Air Temperature Sensor - Auxiliary
2. Lower Air Temperature Sensor - Auxiliary
3. Regulate auxiliary blower motor speed
4. Position the auxiliary air temperature actuator
5. Position the auxiliary mode actuator

Engine Coolant

Engine coolant is the essential element of the heating system. The thermostat controls the normal 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 ambient air drawn through the HVAC module absorbs the heat of the coolant flowing through the heater core. Heated air is distributed to the passenger compartment, through the HVAC module, for passenger comfort. Opening or closing the air temperature door controls the amount of heat delivered to the passenger compartment. The coolant exits the heater core through the return heater hose and recirculated back through the engine cooling system.

Remote Start Activation

The following describes the HVAC control head functionality upon receiving the remote start active serial data message and a power mode status is set to off/awake. The outside air temperature (OAT) sensor on automatic systems, is utilized to determine the moding of the following features: Blower Mode, Bi-level, Floor, Defrost, Recirc and Rear Defrost. Calibratable temperatures are utilized to provide low, mid and high temperature ranges for the selectable feature. Blower and mode have the range to select any valid feature positions. When the remote start active serial data is received, ignition-OFF loop HVAC algorithms will act the same as if a run power mode was received, i.e. re-calibration, afterblow, ignition-OFF motor positioning etc. The OFF timer and the ignition ON timer have the functionality as in the Run mode.

The remote start system operates in one of three zones of operation

1. Cold ambient temperature that is below 5°C (41°F)
2. Hot ambient temperature that is above 30°C (86°F)
3. Mid ambient temperature that is anything between the cold and hot values

1. In cold ambient, the system uses 74°F setpoint, auto blower, defrost mode, rear defrost and/or heated mirrors on, heated seats on, rear in mimic.
2. In mid ambient, the system uses 74°F setpoint, auto blower, auto mode, rear in mimic.
3. In hot ambient, the system uses 74°F setpoint in 2007, in 2008 and beyond a 60°F setpoint will be used, auto blower, auto mode, rear in mimic.

Remote Start De-activation

When the remote start is exited, GMLAN power mode equals run mode or remote start engine. In the case of automatic settings, the displays will revert to the actual state of operation of the features, on the basis of their normal control algorithms.

Special Tools

Illustration Tool Number/Description J 43600 ACR 2000 Air Conditioning Service Center

Scheme 57

See also:
• Diagnostic System Check - Vehicle
• Strategy Based Diagnosis
• Diagnostic Procedure Instructions
• WIRING SYSTEMS AND POWER MANAGEMENT - COMPONENT CONNECTOR END VIEWS - INDEX
• Circuit Testing
• Connector Repairs
• Testing for Intermittent Conditions and Poor Connections
• Wiring Repairs
• Control Module References
• Diagnostic Repair Verification
• Diagnostic Trouble Code (DTC) List - Vehicle
• Air Conditioning (A/C) Refrigerant Pressure Sensor Replacement (Non-HP2)
• Air Conditioning (A/C) Refrigerant Pressure Sensor Replacement (LGH, LML)
• Relay Replacement (Within an Electrical Center)
• Relay Replacement (Attached to Wire Harness)
• Checking Aftermarket Accessories
• Noise Diagnosis - HVAC Module
• Noise Diagnosis - Air Conditioning (A/C) System
• Noise Diagnosis - Blower Motor
• Odor Diagnosis
• Air Conditioning Compressor Replacement (LU3)
• Air Conditioning Compressor Replacement (LZ1, L20, LC9, L9H, L92, LMG)
• Air Delivery Description and Operation
• Air Temperature Description and Operation
• Air Conditioning (A/C) System Performance Test (Gas Engine with Electric Cooling Fan)
• Heating Performance Diagnostic
• Ambient Light Sensor Replacement
• Instrument Panel Accessory Trim Plate Replacement (with RPO SLT)
• Accessory Switch Replacement (without RPO SLT)
• Fastener Caution
• Instrument Panel Inflatable Restraint Module Replacement (Without SLT)
• Actuator Recalibration
• Instrument Panel Service Positioning (without SLT)
• Instrument Panel Service Positioning (with SLT)
• Radio Front Floor Console Speaker Replacement
• Radiator Grille Replacement (GMC)
• Windshield Pillar Garnish Molding Replacement
• DTC B0158, B0163, B0173, B0178, B0509, or B0514
• Air Temperature Description and Operation
• Air Delivery Description and Operation
• Sensor Resistance Table
• Actuator Recalibration