HVAC System - Automatic Chevrolet Silverado 1500

Fastener Tightening Specifications

Fastener Tightening Specifications

Sensor Resistance Table (Primary HVAC)

Sensor Resistance Table (Primary HVAC)

Scheme 28

Scheme 29

Scheme 30

Scheme 31

Scheme 32

Scheme 33

Scheme 34

Scheme 35

Scheme 36

Scheme 37

Scheme 38

Scheme 39

Scheme 40

Scheme 41

Scheme 42

Scheme 43

Scheme 44

A/C Compressor Clutch Connector Parts Information

A/C Compressor Clutch Connector Terminal Identification

Scheme 45

A/C Low Pressure Switch Connector Parts Information

A/C Low Pressure Switch Connector Terminal Identification

Scheme 46

A/C Refrigerant Pressure Sensor Connector Parts Information

A/C Refrigerant Pressure Sensor (Gas) Connector Terminal Identification

Scheme 47

A/C Refrigerant Pressure Sensor (Diesel) Connector Parts Information

A/C Refrigerant Pressure Sensor (Diesel) Connector Terminal Identification

Scheme 48

Air Temperature Actuator - Left Connector Parts Information

Air Temperature Actuator - Left Connector Terminal Identification

Air Temperature Actuator - Right

Air Temperature Actuator - Right Connector Parts Information

Air Temperature Actuator - Right Connector Terminal Identification

Scheme 49

Air Temperature Sensor - Upper Left Connector Parts Information

Air Temperature Sensor - Upper Left Connector Terminal Identification

Air Temperature Sensor - Upper Right

Air Temperature Sensor - Upper Right Connector Parts Information

Air Temperature Sensor - Upper Right Connector Terminal Identification

Air Temperature Sensor - Lower Left

Air Temperature Sensor - Lower Left Connector Parts Information

Air Temperature Sensor - Lower Left Connector Terminal Identification

Air Temperature Sensor - Lower Right

Air Temperature Sensor - Lower Right Connector Parts Information

Air Temperature Sensor - Lower Right Connector Terminal Identification

Scheme 50

Ambient Air Temperature Sensor - HVAC Connector Parts Information

Ambient Air Temperature Sensor - HVAC Connector Terminal Identification

Scheme 51

Ambient Light/Sunload Sensor Assembly Connector Parts Information

Ambient Light/Sunload Sensor Assembly Connector Terminal Identification

Scheme 52

Blower Motor Connector Parts Information

Blower Motor Connector Terminal Identification

Scheme 53

Blower Motor Control Module X1 Connector Parts Information

Blower Motor Control Module X1 Connector Terminal Identification

Scheme 54

Blower Motor Control Module X2 Connector Parts Information

Blower Motor Control Module X2 Connector Terminal Identification

Scheme 55

HVAC Control Module X1 Connector Parts Information

HVAC Control Module X1 Connector Terminal Identification

Scheme 56

HVAC Control Module X2 Connector Parts Information

HVAC Control Module X2 Connector Terminal Identification

Scheme 57

HVAC Control Module X3 Connector Parts Information

HVAC Control Module X3 Connector Terminal Identification

Scheme 58

Inside Air Temperature Sensor - Front Connector Parts Information

Inside Air Temperature Sensor - Front Connector Terminal Identification

Mode Actuator

Mode Actuator Connector Parts Information

Mode Actuator Connector Terminal Identification

Recirculation Actuator

Recirculation Actuator Connector Parts Information

Recirculation Actuator Connector Terminal Identification

DIAGNOSTIC CODE INDEX

DIAGNOSTIC CODE INDEX

Scan Tool Output Controls

HVAC Control Module Scan Tool Output Controls

PCM Scan Tool Output Controls

Rear HVAC/RSA Module

Scan Tool Data List

BCM Scan Tool Data List

HVAC Control Module Scan Tool Data List

PCM Scan Tool Data List

Diagnostic Instructions

1. Perform the «Diagnostic System Check - Vehicle»(/chevrolet/silverado-1500/2007-2007/remont/oem-general-information/#vehicle-diagnostic-information__diagnostic-system-check-vehicle) prior to using this diagnostic procedure.
2. Review «Strategy Based Diagnosis»(/chevrolet/silverado-1500/2007-2007/remont/oem-general-information/#vehicle-diagnostic-information__strategy-based-diagnosis) for an overview of the diagnostic approach.
3. «Diagnostic Procedure Instructions»(/chevrolet/silverado-1500/2007-2007/remont/oem-general-information/#vehicle-diagnostic-information__diagnostic-procedure-instructions) provides an overview of each diagnostic category.

Diagnostic Fault Information

DTC B0158, B0163, B0173, B0178, B0509, or B0514

Circuit/System Description

Air temperature sensors allow the HVAC control module to monitor the temperature of the discharge air in the HVAC ducts. The module applies 5 volts to internal input resistors that are connected to the signal circuits of the air temperature sensors. The module provides ground to the air temperature sensors through the low reference circuit. The HVAC control module monitors the voltage drops across the air temperature sensors and uses the inputs for automatic control calculations. When the duct air temperatures are cold, the resistances of the sensors are high and the voltage signals are high. When the duct air temperatures are hot, the resistances of the sensors are low and the voltage signals are low. The HVAC control module converts the voltage values to count values where one volt is approximately equal to 51 counts.

DTC B0158

This DTC is for the Outside Air Temperature Sensor

DTC B0163

This DTC is for the Passenger Compartment Air Temperature Sensor

DTC B0173

This DTC is for the Left Upper Air Temperature Sensor

DTC B0178

This DTC is for the Left Lower Air Temperature Sensor

DTC B0509

This DTC is for the Right Upper Air Temperature Sensor

DTC B0514

This DTC is for the Right Lower Air Temperature Sensor

Conditions for Running the DTC

The ignition is turned On.

Conditions for Setting the DTC

The HVAC control module detects the signal circuit is less than 0.09 volts (5 counts) or more than 4.90 volts (250 counts).

Action Taken When the DTC Sets

The Auto feature of the HVAC control module will be inoperative.

Conditions for Clearing the DTC

1. The DTC will become history if the HVAC control module no longer detects a failure.
2. The history DTC will clear after 50 fault-free ignition cycles.

Reference Information

Schematic Reference

HVAC Schematics

Connector End View Reference

HVAC Connector End Views

Description and Operation

Air Temperature Description and Operation

Electrical Information Reference

1. «Circuit Testing»(/chevrolet/silverado-1500/2007-2007/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-troubleshooting-diagnosis__circuit-testing)
2. «Connector Repairs»(/chevrolet/silverado-1500/2007-2007/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-troubleshooting-diagnosis__connector-repairs)
3. «Testing for Intermittent Conditions and Poor Connections»(/chevrolet/silverado-1500/2007-2007/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-troubleshooting-diagnosis__testing-for-intermittent-conditions-and-poor)
4. «Wiring Repairs»(/chevrolet/silverado-1500/2007-2007/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-troubleshooting-diagnosis__wiring-repairs)

Scan Tool Reference

1. «Scan Tool Output Controls»(/chevrolet/silverado-1500/2007-2007/remont/automatic-hvac-system/#hvac-system-automatic__scan-tool-output-controls)
2. «Scan Tool Data List»(/chevrolet/silverado-1500/2007-2007/remont/automatic-hvac-system/#hvac-system-automatic__scan-tool-data-list)
3. «Scan Tool Data Definitions»(/chevrolet/silverado-1500/2007-2007/remont/automatic-hvac-system/#hvac-system-automatic)

Circuit/System Testing

1. Ignition OFF, disconnect the harness connector at the appropriate temperature sensor.
2. Ignition OFF, test for less than 1.0 ohm of resistance between the appropriate ground circuit terminal and ground. Duct temperature sensor ground circuit terminal A Ambient temperature sensor ground circuit terminal B Inside air temperature sensor ground circuit terminal C If greater than the specified range, test the ground circuit for an open/high resistance.
3. Ignition ON, verify the appropriate scan tool temperature sensor parameter is greater than 250 counts. If less than the specified range, test the appropriate signal circuit terminal for a short to ground. If the circuit tests normal, replace the HVAC control module. Duct temperature sensor signal circuit terminal B Ambient temperature sensor signal circuit terminal A Inside air temperature sensor signal circuit terminal B
4. Install a 3A fused jumper wire between the appropriate signal circuit terminal and ground. Verify the appropriate scan tool temperature sensor parameter is less than 5 counts. Duct temperature sensor signal circuit terminal B Ambient temperature sensor signal circuit terminal A Inside air temperature sensor signal circuit terminal B If greater than the specified range, test the signal circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the HVAC control module.
5. If all circuits test normal, test or replace the appropriate temperature sensor.

Repair Procedures

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

1. «Air Temperature Sensor Replacement - Lower Left Side»(/chevrolet/silverado-1500/2007-2007/remont/automatic-hvac-system/#hvac-system-automatic)
2. «Air Temperature Sensor Replacement - Lower Right Side»(/chevrolet/silverado-1500/2007-2007/remont/automatic-hvac-system/#hvac-system-automatic)
3. «Ambient Air Temperature Sensor Replacement»(/chevrolet/silverado-1500/2007-2007/remont/automatic-hvac-system/#hvac-system-automatic)
4. «Inside Air Temperature Sensor Assembly Replacement»(/chevrolet/silverado-1500/2007-2007/remont/automatic-hvac-system/#hvac-system-automatic)
5. «Control Module References»(/chevrolet/silverado-1500/2007-2007/remont/communication-devices/#programming-and-setup-all-systems__control-module-references) for HVAC control module replacement, setup, and programming

Circuit Description

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

1. B0183 is for the left sunload sensor.
2. B0188 is for the right sunload sensor.

The left and right sunload sensors provide the HVAC control module with inputs as to the amount heat load the sun is placing on the interior of the vehicle. The sunload sensors are photodiodes that are sensitive to light intensity. The body control module (BCM) applies 5 volts to internal input resistors that are connected to the left and right signal circuits of the sunload sensor assembly. The BCM provides ground to the sensors through the low reference circuit. The BCM monitors the voltage drops across the sunload sensors and converts the voltage values to count values where 1 volt is approximately equal to 51 counts. As the light intensity increases, the sunload sensors allow more current to travel through the circuits and the signal voltages decrease. As the light intensity decreases, the sunload sensors allow less current to travel through the circuits and the signal voltages increase. The BCM transmits the data to the HVAC control module over the GM LAN data circuit.

DTC Descriptors

This diagnostic procedure supports the following DTCs

1. DTC B0183 05 Solar Load Sensor 1 Circuit Short to Short to Battery or Open
2. DTC B0183 02 Solar Load Sensor 1 Circuit Short to Ground
3. DTC B0188 05 Solar Load Sensor 2 Circuit Short to Short to Battery or Open
4. DTC B0188 02 Solar Load Sensor 2 Circuit Short to Ground

The ignition is ON.

The BCM determines that the value of the sunload sensor signal is less than 5 counts or greater than 250 counts.

The action taken will be for the BCM to revert to a calibrated default value.

1. The DTC will become history if the BCM no longer detects a failure.
2. The history DTC will clear after 100 fault-free ignition cycles.
3. The DTC can be cleared with a scan tool.

Test Description

The numbers below refer to the step numbers on the diagnostic table.

1. 2: This step verifies that the value displayed is within the specified range.
2. 3: This step tests for the proper operation of the circuit in the high voltage range.
3. 4: This step tests for the proper operation of the circuit in the low voltage range. If the fuse in the jumper opens when you perform this test, the signal circuit is shorted to voltage.

DTC B0183 or B0188

1. Perform the «Diagnostic System Check - Vehicle»(/chevrolet/silverado-1500/2007-2007/remont/oem-general-information/#vehicle-diagnostic-information__diagnostic-system-check-vehicle) prior to using this diagnostic procedure.
2. Review «Strategy Based Diagnosis»(/chevrolet/silverado-1500/2007-2007/remont/oem-general-information/#vehicle-diagnostic-information__strategy-based-diagnosis) for an overview of the diagnostic approach.
3. «Diagnostic Procedure Instructions»(/chevrolet/silverado-1500/2007-2007/remont/oem-general-information/#vehicle-diagnostic-information__diagnostic-procedure-instructions) provides an overview of each diagnostic category.

DTC B0228, B0413, B0423, or B3779

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-volt 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-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.

DTC B0228

This DTC is for the recirculate actuator.

DTC B0413

This DTC is for the drivers air temperature actuator.

DTC B0423

This DTC is for the passenger air temperature actuator.

DTC B3779

This DTC is for the mode actuator.

1. The ignition is ON.
2. Ignition voltage is between 9-16 volts.
3. 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 7 counts or greater than 250 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 50 fault-free ignition cycles.
3. The DTC can be cleared with a scan tool.

Schematic Reference

HVAC Schematics

Connector End View Reference

HVAC Connector End Views

Description and Operation

1. «Air Delivery Description and Operation»(/chevrolet/silverado-1500/2007-2007/remont/automatic-hvac-system/#hvac-system-automatic__air-delivery-description-and-operation)
2. «Air Temperature Description and Operation»(/chevrolet/silverado-1500/2007-2007/remont/automatic-hvac-system/#hvac-system-automatic__air-temperature-description-and-operation)

Electrical Information Reference

1. «Circuit Testing»(/chevrolet/silverado-1500/2007-2007/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-troubleshooting-diagnosis__circuit-testing)
2. «Connector Repairs»(/chevrolet/silverado-1500/2007-2007/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-troubleshooting-diagnosis__connector-repairs)
3. «Testing for Intermittent Conditions and Poor Connections»(/chevrolet/silverado-1500/2007-2007/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-troubleshooting-diagnosis__testing-for-intermittent-conditions-and-poor)
4. «Wiring Repairs»(/chevrolet/silverado-1500/2007-2007/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-troubleshooting-diagnosis__wiring-repairs)

Scan Tool Reference

1. «Scan Tool Output Controls»(/chevrolet/silverado-1500/2007-2007/remont/automatic-hvac-system/#hvac-system-automatic__scan-tool-output-controls)
2. «Scan Tool Data List»(/chevrolet/silverado-1500/2007-2007/remont/automatic-hvac-system/#hvac-system-automatic__scan-tool-data-list)
3. «Scan Tool Data Definitions»(/chevrolet/silverado-1500/2007-2007/remont/automatic-hvac-system/#hvac-system-automatic)

Circuit/System Verification

Ignition ON, operate the applicable actuator using the HVAC controls. The applicable scan tool parameter should transition from 7 counts to 250 counts.

1. Ignition OFF, disconnect the harness connector at the applicable actuator.
2. Ignition OFF, test for less than 1 ohm of resistance between the low reference circuit terminal 7 and ground. If greater than the specified range, test the low reference circuit for an open/high resistance. If the circuit tests normal, replace the HVAC control module.
3. Ignition ON, test for 4.8-5.2 volts between the 5-volt reference circuit terminal 10 and ground. If greater than the specified range, test the 5-volt reference circuit for a short to voltage. If the circuit tests normal, replace the HVAC control module. If less then specified range, test the 5-volt reference circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the HVAC control module.
4. Verify the applicable scan tool parameter is less than 7 counts. If greater than the specified range, test the signal circuit terminal 9 for a short to ground. If the circuit tests normal, replace the HVAC control module.
5. Install a 3A fused jumper wire between the signal circuit terminal 9 and the low reference circuit terminal 7. Verify the applicable scan tool parameter is greater than 250 counts. If less than the specified range, test the signal circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the HVAC control module.
6. Verify that a test lamp illuminates between the ignition circuit terminal 5 and ground. If the test lamp does not illuminate, test the ignition circuit for a short to ground or an open/high resistance.
7. Test for 2.5 volts between the control circuit terminal 6 and ground. If greater than the specified range, test the control circuit for a short to voltage. If the circuit tests normal, replace the HVAC control module. If less then specified range, test the 5-volt reference circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the HVAC control module.
8. Install a DMM between the control circuit terminal 6 and ground. Command the actuator in each direction. Voltage on the control circuit should change from 0 volts when commanding the actuator in one direction to 5 volts in the other direction and return to 2.5 volts in the at rest state. If the voltage does not change as specified, replace the HVAC control module.
9. If all circuits test normal, test or replace the applicable actuator.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

1. «Recirculation Actuator Replacement»(/chevrolet/silverado-1500/2007-2007/remont/automatic-hvac-system/#hvac-system-automatic)
2. «Mode Actuator Replacement»(/chevrolet/silverado-1500/2007-2007/remont/automatic-hvac-system/#hvac-system-automatic)
3. «Air Temperature Actuator Replacement - Right Side»(/chevrolet/silverado-1500/2007-2007/remont/automatic-hvac-system/#hvac-system-automatic)
4. «Air Temperature Actuator Replacement - Left Side»(/chevrolet/silverado-1500/2007-2007/remont/automatic-hvac-system/#hvac-system-automatic)

The engine control module (ECM) monitors the high side refrigerant pressure through an A/C refrigerant pressure sensor. 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. The ECM sends the A/C pressure data to the body control module (BCM) over the GM LAN serial data circuit. This keeps the high side pressure in a normal operating range. This will prevent the A/C compressor clutch from disengaging under normal operating conditions. The BCM will not request A/C compressor clutch engagement if the A/C pressure is too high.

This diagnostic procedure supports the following DTCs

1. DTC P0532 Air Conditioning (A/C) Refrigerant Pressure Sensor Circuit Low Voltage
2. DTC P0533 Air Conditioning (A/C) Refrigerant Pressure Sensor Circuit High Voltage

The engine is running.

1. A/C pressure of less than 0.3 volts or more than 4.92 volts.
2. The condition must be present for more than 5 seconds.

1. The ECM will not illuminate the malfunction indicator lamp (MIL).
2. The ECM will store the conditions present when the DTC set as Fail Records data only.

1. The history DTC will clear after 40 consecutive warm-up cycles have occurred without a malfunction.
2. The DTC can be cleared by using the scan tool Clear DTC Information function.

Diagnostic Aids

Test the following conditions

1. Visually inspect the sensor for contamination or damage.
2. Inspect for the following that may affect the sensors accuracy: A malfunction within the refrigerant system causing low pressure Visually inspect the A/C components and lines for damage.
3. Refer to «Testing for Intermittent Conditions and Poor Connections»(/chevrolet/silverado-1500/2007-2007/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-troubleshooting-diagnosis__testing-for-intermittent-conditions-and-poor) .

The numbers below refer to the step numbers on the diagnostic table.

1. 4: This step tests for the proper operation of the circuit in the low voltage range.
2. 5: This step tests for the proper operation of the circuit in the high voltage range. If the fuse in the jumper opens when you perform this test, the signal circuit is shorted to ground.
3. 6: This step tests for a short to voltage in the 5-volt reference circuit.
4. 7: This step tests for a high resistance or an open in the low reference circuit.

DTC P0532 or P0533

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 via an internal solid state device called a driver. The primary function of the driver is to supply the ground for the component being controlled. The driver has a fault line which is monitored by the ECM. When the ECM is commanding a component ON, the voltage of the control circuit should be near 0 volts. When the ECM is commanding the control circuit to a component OFF, the voltage potential of the circuit should be near battery voltage. If the fault detection circuit senses a voltage other than what is expected, this DTC will set.

The ECM will monitor the control circuit for the following

1. A short to ground
2. A short to voltage
3. An open circuit
4. An open relay coil
5. An internally shorted or excessively low resistance relay coil

When the ECM detects any of the above malfunctions, this DTC is set and the affected driver is disabled.

This diagnostic procedure supports the following DTC

DTC P0645 Air Conditioning (A/C) Clutch Relay Control Circuit

1. The ignition voltage is between 9-18 volts.
2. The engine speed is more than 80 RPM.
3. The ECM driver transitions from ON to OFF or from OFF to ON.

The ECM detects an open on the control circuit of the A/C compressor clutch relay.

1. The ECM will not illuminate the malfunction indicator lamp (MIL).
2. 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.

1. A History DTC clears after 40 consecutive warm-up cycles have occurred without a malfunction.
2. The DTC can be cleared by using a scan tool.

If DTC P0645 cannot be duplicated, reviewing the Failure Records vehicle millage since the diagnostic test last failed may help determine how often the condition that caused the DTC to set occurs. This may assist in diagnosing the condition.

If the condition is not present, refer to Testing for Intermittent Conditions and Poor Connections .

The numbers below refer to the step numbers on the diagnostic table.

1. 2: Listen for an audible click when the A/C compressor clutch relay operates. Command both the ON and OFF states. Repeat the commands as necessary.
2. 3: This step tests for voltage at the coil side of the A/C compressor clutch relay. The 10-amp fuse supplies power to the coil side of the A/C compressor clutch relay.
3. 4: This step verifies that the engine control module is providing ground to the A/C compressor clutch relay. If light always on circuit shorted to ground.
4. 8: This step tests for a short to voltage or an open.
5. 10: If the A/C fuse is open be sure to test the A/C compressor clutch supply voltage circuit for a short to ground.

DTC P0645

1. Perform the «Diagnostic System Check - Vehicle»(/chevrolet/silverado-1500/2007-2007/remont/oem-general-information/#vehicle-diagnostic-information__diagnostic-system-check-vehicle) prior to using this diagnostic procedure.
2. Review «Strategy Based Diagnosis»(/chevrolet/silverado-1500/2007-2007/remont/oem-general-information/#vehicle-diagnostic-information__strategy-based-diagnosis) for an overview of the diagnostic approach.
3. «Diagnostic Procedure Instructions»(/chevrolet/silverado-1500/2007-2007/remont/oem-general-information/#vehicle-diagnostic-information__diagnostic-procedure-instructions) provides an overview of each diagnostic category.

DTC P0646 or P0647

The engine control module (ECM)/powertrain control module (PCM) controls the A/C compressor clutch based on an A/C request serial data message from the HVAC control module. The ECM/PCM monitors the A/C refrigerant pressure sensor and if pressure is within a specified range, will engage the A/C compressor by grounding the A/C compressor clutch relay control circuit.

B+ is applied to the A/C relay in the RUN/START position and with the A/C compressor clutch relay control circuit grounded by the ECM/PCM, current flows through the coil side of the A/C relay. With current flowing through the coil side of the relay, a magnetic field is created which pulls the switch side of the relay closed, sending current to the A/C compressor clutch, allowing the A/C compressor to be engaged.

An A/C request is received from the HVAC module.

A short to voltage, short to ground, or open/high resistance is seen on the A/C compressor clutch relay control circuit.

DTC P0646 and DTC P0647 are Type C DTCs

DTC P0646 and DTC P0647 are Type C DTCs

Schematic Reference

HVAC Schematics

Connector End View Reference

HVAC Connector End Views

Description and Operation

Air Temperature Description and Operation

Electrical Information Reference

1. «Circuit Testing»(/chevrolet/silverado-1500/2007-2007/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-troubleshooting-diagnosis__circuit-testing)
2. «Connector Repairs»(/chevrolet/silverado-1500/2007-2007/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-troubleshooting-diagnosis__connector-repairs)
3. «Testing for Intermittent Conditions and Poor Connections»(/chevrolet/silverado-1500/2007-2007/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-troubleshooting-diagnosis__testing-for-intermittent-conditions-and-poor)
4. «Wiring Repairs»(/chevrolet/silverado-1500/2007-2007/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-troubleshooting-diagnosis__wiring-repairs)

DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

Scan Tool Reference

Scan Tool Output Controls

Engine running, command the A/C Relay On and OFF with a scan tool. The A/C compressor clutch should engage and disengage.

1. Ignition OFF, disconnect the A/C relay.
2. Ignition ON, verify a test lamp illuminates between the relay coil B+ circuit terminal and ground. If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance.
3. Connect a test lamp between the relay coil B+ circuit terminal and the A/C compressor clutch relay control circuit terminal.
4. Engine running, command the A/C relay ON and OFF. The test lamp should turn ON and OFF when changing between the commanded states. If the test lamp is always ON, test the control circuit for a short to ground. If the circuit tests normal, replace the ECM/PCM. If the test lamp is always OFF< test the control circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the ECM/PCM.
5. If all circuits test normal, test or replace the A/C relay.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

Control Module References for ECM/PCM 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»(/chevrolet/silverado-1500/2007-2007/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-troubleshooting-diagnosis__checking-aftermarket-accessories) .
2. Inspect the easily accessible or visible system components for obvious damage or conditions which could cause the symptom.
3. Verify the A/C compressor clutch turns freely and is not seized.
4. The A/C compressor will not operate in cold outside air temperatures. Refer to «Air Temperature Description and Operation»(/chevrolet/silverado-1500/2007-2007/remont/manual-hvac-system/#hvac-system-manual__air-temperature-description-and-operation) .
5. The following conditions may cause window fogging: Wet carpet or mats High humidity Interior water leak Blocked A/C evaporator drain tube Maximum passenger capacity Blocked body pressure relief valves
6. Inspect the air distribution system for causes of reduced air flow: Obstructed or dirty passenger compartment air filter, if equipped. Blocked or damaged air inlet or outlet vents.

Intermittent

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

Symptom List

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

1. «HVAC Compressor Clutch Does Not Engage»(/chevrolet/silverado-1500/2007-2007/remont/manual-hvac-system/#hvac-system-manual)
2. «HVAC Compressor Clutch Does Not Disengage»(/chevrolet/silverado-1500/2007-2007/remont/manual-hvac-system/#hvac-system-manual)
3. «Blower Motor Always On»(/chevrolet/silverado-1500/2007-2007/remont/manual-hvac-system/#hvac-system-manual)
4. «Blower Motor Inoperative»(/chevrolet/silverado-1500/2007-2007/remont/manual-hvac-system/#hvac-system-manual__blower-motor-inoperative)
5. «Blower Motor Malfunction»(/chevrolet/silverado-1500/2007-2007/remont/manual-hvac-system/#hvac-system-manual)
6. «Too Hot in Vehicle»(/chevrolet/silverado-1500/2007-2007/remont/manual-hvac-system/#hvac-system-manual__too-hot-in-vehicle)
7. «Too Cold in Vehicle»(/chevrolet/silverado-1500/2007-2007/remont/manual-hvac-system/#hvac-system-manual__too-cold-in-vehicle)
8. «Air Delivery Improper»(/chevrolet/silverado-1500/2007-2007/remont/manual-hvac-system/#hvac-system-manual)
9. «Air Recirculation Malfunction»(/chevrolet/silverado-1500/2007-2007/remont/manual-hvac-system/#hvac-system-manual__air-recirculation-malfunction)
10. «Leak Testing»(/chevrolet/silverado-1500/2007-2007/remont/automatic-hvac-system/#heating-ventilation-and-air-conditioning__leak-testing) .
11. «Noise Diagnosis - Blower Motor»(/chevrolet/silverado-1500/2007-2007/remont/automatic-hvac-system/#heating-ventilation-and-air-conditioning__noise-diagnosis-blower-motor) .
12. «Noise Diagnosis - Air Conditioning (A/C) System»(/chevrolet/silverado-1500/2007-2007/remont/automatic-hvac-system/#heating-ventilation-and-air-conditioning__noise-diagnosis-air-conditioning-ac) .
13. «Noise Diagnosis - HVAC Module»(/chevrolet/silverado-1500/2007-2007/remont/automatic-hvac-system/#heating-ventilation-and-air-conditioning__noise-diagnosis-hvac-module) .
14. «Odor Diagnosis»(/chevrolet/silverado-1500/2007-2007/remont/automatic-hvac-system/#heating-ventilation-and-air-conditioning__odor-diagnosis) .

A/C compressor clutch will not engage under the following conditions

1. The A/C high side line pressure is over 2957 kPa (429 psi).
2. The A/C low side line pressure is under 138-172 kPa (20-25 psi).
3. Throttle angle is at 100 percent.
4. Engine speed is more than 5,500 RPM.
5. Engine coolant temperature (ECT) is more than 121°C (250°F).
6. Ambient air temperature is less than 5°C (40°F).
7. Engine is idling at a low unstable RPM

Compressor clutch engagement cannot be used to determine status of the low pressure switch. The low pressure switch is one of several inputs to the HVAC control module for A/C request authorization. A/C request is one of several inputs to the engine control module (ECM) that control A/C compressor clutch engagement.

To accurately determine what pressure the A/C low pressure switch opens and closes at use Kent Moore GE-47742 which will allow the technician to measure the switch point pressure at the switch.

Using a scan tool, monitor the "low pressure switch" status while monitoring the "low side" pressure at the switch to determine the switch points of the low pressure switch.

The low pressure switch "connector seal" must be removed before plugging it into the switch for testing. The "plunger effect" of plugging the connector with seal into the switch induces a pressure on the back side of the switch, this pressure will skew the opening/closing characteristics of the switch 5-10 psi until the pressure bleeds off. The time required for the connection induced pressure to bleed off can take 20 minutes or longer.

The numbers below refer to the step numbers on the diagnostic table.

1. 2: The A/C compressor output is disabled if the engine is idling at a low unstable RPM.
2. 3: The A/C compressor relay output is disabled if engine coolant temperature is above 121°C (250°F). The engine coolant indicator will illuminate at this temperature.
3. 4: This step ensures that the HVAC control module is receiving an input from the A/C switch.
4. 5: These actions will enable the A/C compressor to operate.
5. 6: This test ensures that there is sufficient refrigerant in the A/C system. The specific values come from the A/C System Performance Test.
6. 8: The A/C Low Pressure Switch parameter is out of range when the HVAC control module interprets the signal being below 138-172 kPa (20-25 psi).
7. 9: This action will simulate a closed switch condition. If the Pressure Cycle Switch parameter reads Low Pressure than there is a circuit condition or a condition with the HVAC control module.
8. 12: The A/C compressor relay output from the ECM is disabled if the A/C high side system pressure is interpreted to be higher than 2 958 kPa (429 psi).

HVAC Compressor Clutch Does Not Engage

The number below refers to the step number on the diagnostic table.

1. 2: These actions will disable the HVAC control module output to powertrain control module (PCM) or engine control module (ECM).

HVAC Compressor Clutch Does Not Disengage

The number below refers to the step number on the diagnostic table.

1. 4: The blower motor parameter must be commanded ON before an OFF command will function.

Blower Motor Always On

Blower Motor Inoperative

Blower Motor Inoperative

The numbers below refer to the step numbers on the diagnostic table.

1. 2: This step verifies that the HVAC control module Fan Up Switch parameter matches the requested state of the blower motor switch.
2. 3: This step verifies that the HVAC control module Fan Down Switch parameter matches the requested state of the blower motor switch.

Blower Motor Malfunction

Too Hot in Vehicle

Too Hot in Vehicle

Too Cold in Vehicle

Too Cold in Vehicle

1. The condition may be intermittent. Refer to «Testing for Intermittent Conditions and Poor Connections»(/chevrolet/silverado-1500/2007-2007/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-troubleshooting-diagnosis__testing-for-intermittent-conditions-and-poor) .
2. Inspect the air delivery system for the following conditions: A dirty HVAC air filter, if applicable An obstruction to the airflow Air leaks Misaligned air ducts Broken or binding linkages or doors

Air Delivery Improper

Air Recirculation Malfunction

Air Recirculation Malfunction

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 59

HVAC Control Module Replacement

Removal Procedure

Note. In order to avoid actuator damage, DO NOT apply power to the actuator when it is not installed in the HVAC module.

1. Remove the air distribution duct. Refer to «Air Distributor Duct Replacement»(/chevrolet/silverado-1500/2007-2007/remont/automatic-hvac-system/#heating-ventilation-and-air-conditioning) .
2. Disconnect the electrical connection from the recirculation actuator (1).
3. Remove the recirculation actuator retaining screws.
4. Remove the recirculation actuator.

Installation Procedure

1. Install the recirculation actuator.
2. Install the recirculation actuator retaining screws. Tighten: Tighten the screws to 1.6 N.m (14 lb in).
3. Connect the electrical connector to the recirculation actuator (1).
4. Install the air distribution duct. Refer to «Air Distributor Duct Replacement»(/chevrolet/silverado-1500/2007-2007/remont/automatic-hvac-system/#heating-ventilation-and-air-conditioning) .
5. Re-calibrate the recirculation actuator. Refer to «Actuator Recalibration»(/chevrolet/silverado-1500/2007-2007/remont/automatic-hvac-system/#hvac-system-automatic__actuator-recalibration) .

Scheme 60

Mode Actuator Replacement

Scheme 61

Air Temperature Actuator Replacement - Right Side

Scheme 62

Air Temperature Actuator Replacement - Left Side

Scheme 63

Air Temperature Sensor Replacement - Lower Left Side

Scheme 64

Air Temperature Sensor Replacement - Lower Right Side

Scheme 65

Ambient Air Temperature Sensor Replacement

1. Remove the left windshield garnish molding. Refer to «Windshield Pillar Garnish Molding Replacement»(/chevrolet/silverado-1500/2007-2007/remont/exteriorinterior-trim/#interior-trim-and-paneling) .
2. Remove the left center pillar assist handle. Refer to «Roof Rail Rear Assist Handle Replacement»(/chevrolet/silverado-1500/2007-2007/remont/exteriorinterior-trim/#interior-trim-and-paneling) .
3. Remove the center pillar garnish molding. Refer to «Center Pillar Upper Garnish Molding Replacement»(/chevrolet/silverado-1500/2007-2007/remont/exteriorinterior-trim/#interior-trim-and-paneling) .
4. Remove the left sunshade. Refer to «Sunshade Replacement»(/chevrolet/silverado-1500/2007-2007/remont/exteriorinterior-trim/#interior-trim-and-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»(/chevrolet/silverado-1500/2007-2007/remont/exteriorinterior-trim/#interior-trim-and-paneling) .
5. Install the left center pillar garnish molding. Refer to «Center Pillar Upper Garnish Molding Replacement»(/chevrolet/silverado-1500/2007-2007/remont/exteriorinterior-trim/#interior-trim-and-paneling) .
6. Install the left center assist handle. Refer to «Roof Rail Rear Assist Handle Replacement»(/chevrolet/silverado-1500/2007-2007/remont/exteriorinterior-trim/#interior-trim-and-paneling) .
7. Install the left windshield garnish molding. Refer to «Windshield Pillar Garnish Molding Replacement»(/chevrolet/silverado-1500/2007-2007/remont/exteriorinterior-trim/#interior-trim-and-paneling) .

Scheme 66

Sun Load 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 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

Air Delivery Description and Operation

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.

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 processor controls the speed of the blower motor by increasing or decreasing the voltage drop on the ground side of the blower motor. The HVAC control module provides a low side pulse width modulated signal to the blower motor control processor over the blower motor speed control circuit. As the requested blower speed increases, the HVAC control module increases the amount of time that the speed signal is modulated to ground. As the requested blower speed decreases, the HVAC control module decreases the amount of time that the signal is modulated to ground.

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 low side pulse width modulated 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 processor supplies a 5-volt reference to the HVAC control module on the blower motor speed control circuit. The 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 blower motor control processor through the battery positive voltage and ground circuits. 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.

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 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. These features are determined by the IAT during activation sequence and are maintained for the duration of engine run time. 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 10°C (50°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

HVAC Control Components

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

Air Temperature Description and Operation

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

Air Temperature Description and Operation

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.

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.

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. These features are determined by the intake air temperature (IAT) during activation sequence and are maintained for the duration of engine run time. 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 10°C (50°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.

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

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

Scheme 67

See also:
• Diagnostic System Check - Vehicle
• Strategy Based Diagnosis
• Diagnostic Procedure Instructions
• Circuit Testing
• Connector Repairs
• Testing for Intermittent Conditions and Poor Connections
• Wiring Repairs
• Diagnostic Repair Verification
• Control Module References
• Air Conditioning (A/C) Refrigerant Pressure Sensor Replacement
• Powertrain Diagnostic Trouble Code (DTC) Type Definitions
• Air Delivery Description and Operation
• Air Temperature Description and Operation
• Checking Aftermarket Accessories
• HVAC Compressor Clutch Does Not Engage
• Blower Motor Inoperative
• Too Hot in Vehicle
• Too Cold in Vehicle
• Air Recirculation Malfunction
• Leak Testing
• Noise Diagnosis - Blower Motor
• Noise Diagnosis - Air Conditioning (A/C) System
• Noise Diagnosis - HVAC Module
• Odor Diagnosis
• Symptoms - Engine Controls
• Engine Overheating
• Air Conditioning (A/C) System Performance Test (Gas Engine w/Engine Driven Fan)
• Actuator Recalibration
• Diagnostic Trouble Code (DTC) List - Vehicle
• Heating Performance Diagnostic
• Instrument Panel Accessory Trim Plate Replacement (without RPO SLT)
• Fastener Notice
• Radiator Grille Replacement (GMC)
• Windshield Pillar Garnish Molding Replacement
• DTC B0158, B0163, B0173, B0178, B0509, or B0514
• Air Temperature Description and Operation
• Scan Tool Output Controls
• Scan Tool Data List
• Sensor Resistance Table (Primary HVAC)
• Air Delivery Description and Operation
• Actuator Recalibration