HVAC System - Automatic: Other Chevrolet Traverse I

Sensor Resistance Table

Scheme 74

Scheme 75

Scheme 76

Scheme 77

Scheme 78

Reference Information

Schematic Reference

HVAC Schematics

Connector End View Reference

Component Connector End Views

Description and Operation

1. «Air Temperature Description and Operation»(ref-365293-S39512887082010070600000)
2. «Air Delivery Description and Operation»(ref-365293-S15177643062010070600000)

Electrical Information Reference

1. «Circuit Testing»(ref-365275-S00040570812010070600000)
2. «Connector Repairs»(ref-365275-S19060558252010070600000)
3. «Testing for Intermittent Conditions and Poor Connections»(ref-365275-S00287822652010070600000)
4. «Wiring Repairs»(ref-365275-S21384576672010070600000)

Scan Tool Reference

Control Module References for scan tool information

Circuit/System Verification

Ignition ON, observe the scan tool Outside Air Temp. Sensor Raw parameter. The reading should be between -35°C (-39°F) and 85°C (185°F) and change with ambient air temperature changes.

Repair Procedures

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

1. «Ambient Air Temperature Sensor Replacement»(ref-365293-S02259717912010070600000)
2. «Control Module References»(ref-365276-S01454229382010070600000) for HVAC control module replacement, setup, and programming

Schematic Reference

HVAC Schematics

Connector End View Reference

Component Connector End Views

Description and Operation

1. «Air Temperature Description and Operation»(ref-365293-S39512887082010070600000)
2. «Air Delivery Description and Operation»(ref-365293-S15177643062010070600000)

Electrical Information Reference

1. «Circuit Testing»(ref-365275-S00040570812010070600000)
2. «Connector Repairs»(ref-365275-S19060558252010070600000)
3. «Testing for Intermittent Conditions and Poor Connections»(ref-365275-S00287822652010070600000)
4. «Wiring Repairs»(ref-365275-S21384576672010070600000)

Scan Tool Reference

Control Module References for scan tool information

Ignition ON, observe the scan tool Inside Air Temperature Sensor parameter. The reading should be between -35°C (-39°F) and 98°C (208°F) and change with inside air temperature changes.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

1. «Inside Air Temperature Sensor Aspirator Replacement»(ref-365293-S07175053742010070600000)
2. «Control Module References»(ref-365276-S01454229382010070600000) for HVAC control module replacement, setup and programming

Schematic Reference

HVAC Schematics

Connector End View Reference

Component Connector End Views

Description and Operation

1. «Air Temperature Description and Operation»(ref-365293-S39512887082010070600000)
2. «Air Delivery Description and Operation»(ref-365293-S15177643062010070600000)

Electrical Information Reference

1. «Circuit Testing»(ref-365275-S00040570812010070600000)
2. «Connector Repairs»(ref-365275-S19060558252010070600000)
3. «Testing for Intermittent Conditions and Poor Connections»(ref-365275-S00287822652010070600000)
4. «Wiring Repairs»(ref-365275-S21384576672010070600000)

Scan Tool Reference

Control Module References for scan tool information

Ignition ON, observe the appropriate scan tool air duct temperature sensor. The reading should be between -35°C (-39°F) and 98°C (208°F) and change with duct air temperature changes.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

1. «Duct Air Temperature Sensor Replacement - Upper Right Side»(ref-365293-S04831888682010070600000)
2. «Duct Air Temperature Sensor Replacement - Upper Left Side»(ref-365293-S12229562792010070600000)
3. «Duct Air Temperature Sensor Replacement - Lower Left Side»(ref-365293-S37075198982010070600000)
4. «Duct Air Temperature Sensor Replacement - Lower Right Side»(ref-365293-S30810056772010070600000)
5. «Control Module References»(ref-365276-S01454229382010070600000) for HVAC control module replacement, setup and programming

Schematic Reference

HVAC Schematics

Connector End View Reference

Component Connector End Views

Description and Operation

1. «Air Temperature Description and Operation»(ref-365293-S39512887082010070600000)
2. «Air Delivery Description and Operation»(ref-365293-S15177643062010070600000)

Electrical Information Reference

1. «Circuit Testing»(ref-365275-S00040570812010070600000)
2. «Connector Repairs»(ref-365275-S19060558252010070600000)
3. «Testing for Intermittent Conditions and Poor Connections»(ref-365275-S00287822652010070600000)
4. «Wiring Repairs»(ref-365275-S21384576672010070600000)

Scan Tool Reference

Control Module References for scan tool information

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

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

1. «Daytime Running Lamp (DRL) Ambient Light Sensor Replacement (With UV6)»(ref-365239-S18984478512010070600000) or «Daytime Running Lamp (DRL) Ambient Light Sensor Replacement (Without UV6)»(ref-365239-S31429892092010070600000)
2. «Control Module References»(ref-365276-S01454229382010070600000) for HVAC control module replacement, setup, and programming

Schematic Reference

HVAC Schematics

Connector End View Reference

Component Connector End Views

Description and Operation

1. «Air Delivery Description and Operation»(ref-365293-S15177643062010070600000)
2. «Air Temperature Description and Operation»(ref-365293-S39512887082010070600000)

Electrical Information Reference

1. «Circuit Testing»(ref-365275-S00040570812010070600000)
2. «Connector Repairs»(ref-365275-S19060558252010070600000)
3. «Testing for Intermittent Conditions and Poor Connections»(ref-365275-S00287822652010070600000)
4. «Wiring Repairs»(ref-365275-S21384576672010070600000)

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.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

1. «Air Inlet Valve Actuator Replacement»(ref-365293-S34318144572010070600000)
2. «Mode Valve Actuator Replacement»(ref-365293-S07914770242010070600000)
3. «Temperature Valve Actuator Replacement - Left Side»(ref-365293-S26051587352010070600000)
4. «Temperature Valve Actuator Replacement - Right Side»(ref-365293-S10691364412010070600000)
5. «Auxiliary Temperature Valve Actuator Replacement»(ref-365293-S34049687012010070600000)
6. «Auxiliary Mode Valve Actuator Replacement»(ref-365293-S01182652862010070600000)
7. «Control Module References»(ref-365276-S01454229382010070600000) for HVAC control module and HVAC Auxiliary control module or rear seat audio (RSA) replacement, setup, and programming

Schematic Reference

HVAC Schematics

Connector End View Reference

Component Connector End Views

Description and Operation

1. «Air Delivery Description and Operation»(ref-365293-S15177643062010070600000) Air Temperature Description and Operation
2. «Air Temperature Description and Operation»(ref-365293-S39512887082010070600000) Air Delivery Description and Operation

Electrical Information Reference

1. «Circuit Testing»(ref-365275-S00040570812010070600000)
2. «Connector Repairs»(ref-365275-S19060558252010070600000)
3. «Testing for Intermittent Conditions and Poor Connections»(ref-365275-S00287822652010070600000)
4. «Wiring Repairs»(ref-365275-S21384576672010070600000)

Scan Tool Reference

Control Module References for scan tool information

1. Reprogram the HVAC control module. The module should successfully reprogram. If the module will not reprogram, replace the HVAC control module that set the DTC.
2. With a scan tool, clear the DTC.
3. Ignition OFF.
4. Wait 60 seconds, then recheck for DTCs. DTC B1023 should not set. If DTC B1023 sets, replace the module.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

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

Schematic Reference

HVAC Schematics

Connector End View Reference

Component Connector End Views

Description and Operation

1. «Air Temperature Description and Operation»(ref-365293-S39512887082010070600000)
2. «Air Delivery Description and Operation»(ref-365293-S15177643062010070600000)

Electrical Information Reference

1. «Circuit Testing»(ref-365275-S00040570812010070600000)
2. «Connector Repairs»(ref-365275-S19060558252010070600000)
3. «Testing for Intermittent Conditions and Poor Connections»(ref-365275-S00287822652010070600000)
4. «Wiring Repairs»(ref-365275-S21384576672010070600000)

Scan Tool Reference

Control Module References for scan tool information

Ignition ON, observe the scan tool A/C Evaporator Temperature Sensor parameter. The reading should be between -39°F (-35°C) and 208°F (98°C) and change with evaporator air temperature changes.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

1. «Evaporator Air Temperature Sensor Replacement»(ref-365250-S36639118632010070600000)
2. «Control Module References»(ref-365276-S01454229382010070600000) for HVAC control module replacement, setup, and programming

Schematic Reference

HVAC Schematics

Connector End View Reference

Component Connector End Views

Description and Operation

1. «Air Temperature Description and Operation»(ref-365293-S39512887082010070600000)
2. «Air Delivery Description and Operation»(ref-365293-S15177643062010070600000)

Electrical Information Reference

1. «Circuit Testing»(ref-365275-S00040570812010070600000)
2. «Connector Repairs»(ref-365275-S19060558252010070600000)
3. «Testing for Intermittent Conditions and Poor Connections»(ref-365275-S00287822652010070600000)
4. «Wiring Repairs»(ref-365275-S21384576672010070600000)

Scan Tool Reference

Control Module References for scan tool information

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

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

1. «Air Conditioning (A/C) Refrigerant Pressure Sensor Replacement»(ref-365250-S27998768792010070600000)
2. «Control Module References»(ref-365276-S01454229382010070600000) for the ECM replacement, setup, and programming

Conditions for Setting the DTCs

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

Schematic Reference

HVAC Schematics

Connector End View Reference

Component Connector End Views

Description and Operation

1. «Air Delivery Description and Operation»(ref-365293-S15177643062010070600000)
2. «Air Temperature Description and Operation»(ref-365293-S39512887082010070600000)

Electrical Information Reference

1. «Circuit Testing»(ref-365275-S00040570812010070600000)
2. «Connector Repairs»(ref-365275-S19060558252010070600000)
3. «Testing for Intermittent Conditions and Poor Connections»(ref-365275-S00287822652010070600000)
4. «Wiring Repairs»(ref-365275-S21384576672010070600000)

Scan Tool Reference

Control Module References for scan tool information

Engine running place the mode switch in the defrost position. The A/C compressor clutch should engage.

1. If the clutch does not engage refer to «Air Conditioning (A/C) System Performance Test»(ref-365250-S20402374852010070600000)

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

1. «Air Conditioning Compressor Replacement»(ref-365250-S28333470572010070600000)
2. «Relay Replacement (Attached to Wire Harness)»(ref-365277-S15413989202010070600000)
3. «Air Conditioning Clutch Assembly Replacement»(ref-365250-S33704928442010070600000)
4. «Control Module References»(ref-365276-S01454229382010070600000) for HVAC control module and ECM replacement, setup, and programming

Symptoms - HVAC Systems - Automatic

Intermittent

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

Schematic Reference

HVAC Schematics

Connector End View Reference

Component Connector End Views

Description and Operation

1. «Air Temperature Description and Operation»(ref-365293-S39512887082010070600000)
2. «Air Delivery Description and Operation»(ref-365293-S15177643062010070600000)

Electrical Information Reference

1. «Circuit Testing»(ref-365275-S00040570812010070600000)
2. «Connector Repairs»(ref-365275-S19060558252010070600000)
3. «Testing for Intermittent Conditions and Poor Connections»(ref-365275-S00287822652010070600000)
4. «Wiring Repairs»(ref-365275-S21384576672010070600000)

Scan Tool Reference

Control Module References for scan tool information

Engine running place the mode switch in the defrost position. The A/C compressor clutch should engage.

1. If the clutch does not engage refer to «Air Conditioning (A/C) System Performance Test»(ref-365250-S20402374852010070600000)

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

1. «Air Conditioning Compressor Replacement»(ref-365250-S28333470572010070600000)
2. «Relay Replacement (Attached to Wire Harness)»(ref-365277-S15413989202010070600000)
3. «Air Conditioning Clutch Assembly Replacement»(ref-365250-S33704928442010070600000)
4. «Control Module References»(ref-365276-S01454229382010070600000) for HVAC control module and ECM replacement, setup, and programming

Schematic Reference

HVAC Schematics

Connector End View Reference

Component Connector End Views

Description and Operation

1. «Air Delivery Description and Operation»(ref-365294-S35110782462010070600000)
2. «Air Temperature Description and Operation»(ref-365294-S21548389072010070600000)

Electrical Information Reference

1. «Circuit Testing»(ref-365275-S00040570812010070600000)
2. «Connector Repairs»(ref-365275-S19060558252010070600000)
3. «Testing for Intermittent Conditions and Poor Connections»(ref-365275-S00287822652010070600000)
4. «Wiring Repairs»(ref-365275-S21384576672010070600000)

Scan Tool Reference

Control Module References for scan tool information

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

1. «Blower Motor Replacement»(ref-365250-S08866902292010070600000)
2. «Control Module References»(ref-365276-S01454229382010070600000) for blower motor control module and HVAC control module setup, replacement, and programming

Schematic Reference

HVAC Schematics

Connector End View Reference

Component Connector End Views

Description and Operation

1. «Air Delivery Description and Operation»(ref-365294-S35110782462010070600000)
2. «Air Temperature Description and Operation»(ref-365294-S21548389072010070600000)

Electrical Information Reference

1. «Circuit Testing»(ref-365275-S00040570812010070600000)
2. «Connector Repairs»(ref-365275-S19060558252010070600000)
3. «Testing for Intermittent Conditions and Poor Connections»(ref-365275-S00287822652010070600000)
4. «Wiring Repairs»(ref-365275-S21384576672010070600000)

Scan Tool Reference

Control Module References for scan tool information

Ignition ON, command the auxiliary blower motor ON and OFF with a scan tool. Observe that the auxiliary blower motor turns ON and OFF with each command.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

1. «Auxiliary Blower Motor Replacement»(ref-365250-S07699237942010070600000)
2. «Control Module References»(ref-365276-S01454229382010070600000) for auxiliary blower motor control module and HVAC control module replacement, setup, and programming

Schematic Reference

HVAC Schematics

Connector End View Reference

Component Connector End Views

Description and Operation

1. «Air Delivery Description and Operation»(ref-365293-S15177643062010070600000)
2. «Air Temperature Description and Operation»(ref-365293-S39512887082010070600000)

Electrical Information Reference

1. «Circuit Testing»(ref-365275-S00040570812010070600000)
2. «Connector Repairs»(ref-365275-S19060558252010070600000)
3. «Testing for Intermittent Conditions and Poor Connections»(ref-365275-S00287822652010070600000)
4. «Wiring Repairs»(ref-365275-S21384576672010070600000)

Scan Tool Reference

Control Module References for scan tool information

1. Ignition ON, cover the sunload sensor assembly with a shop towel or other suitable item. 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 Sun Load Sensor Circuit Malfunction below.
2. Remove the shop towel and shine an incandescent light on the sunload sensor assembly. 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 Sun Load Sensor Circuit Malfunction below.
3. Measure actual outside air temperature using a thermometer. Compare this value to the scan tool Outside Air Temp. Raw parameter. The measured temperature should be within 5 degrees of parameter. If not within the specified range, refer to Ambient / Inside Air Temperature Sensor Circuit Malfunction below.
4. Measure actual inside air temperature using a thermometer. Compare this value to the scan tool Inside Air Temp. parameter. The measured temperature should be within 5 degrees of parameter. If not within the specified range, refer to Ambient / Inside Air Temperature Sensor Circuit Malfunction below.
5. Measure actual temperature using a thermometer at each of the duct temperature sensors. Compare this value to the appropriate scan tool Duct Actual parameter. The measured temperature should be within 5 degrees of appropriate Duct Actual parameter. If not within the specified range, refer to Duct Temperature / Evaporator Temperature Sensor Circuit Malfunction below.
6. Measure actual temperature using a thermometer at the A/C evap. temperature sensor. Compare this value to the scan tool A/C Evap. Temperature Sensor parameter. The measured temperature should be within 5 degrees of the parameter. If not within the specified range, refer to Duct Temperature / Evaporator Temperature Sensor Circuit Malfunction below.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

1. «Duct Air Temperature Sensor Replacement - Upper Right Side»(ref-365293-S04831888682010070600000)
2. «Duct Air Temperature Sensor Replacement - Upper Left Side»(ref-365293-S12229562792010070600000)
3. «Duct Air Temperature Sensor Replacement - Lower Left Side»(ref-365293-S37075198982010070600000)
4. «Duct Air Temperature Sensor Replacement - Lower Right Side»(ref-365293-S30810056772010070600000)
5. «Ambient Air Temperature Sensor Replacement»(ref-365293-S02259717912010070600000)
6. «Evaporator Air Temperature Sensor Replacement»(ref-365250-S36639118632010070600000)
7. «Daytime Running Lamp (DRL) Ambient Light Sensor Replacement (With UV6)»(ref-365239-S18984478512010070600000) or «Daytime Running Lamp (DRL) Ambient Light Sensor Replacement (Without UV6)»(ref-365239-S31429892092010070600000)
8. «Inside Air Temperature Sensor Aspirator Replacement»(ref-365293-S07175053742010070600000)
9. «Control Module References»(ref-365276-S01454229382010070600000) for HVAC 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. Select HVAC Module.
4. Select HVAC Systems Automatic or Manual.
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 the blower motor will operate 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

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 (without RSA)

The Auxiliary HVAC Control Module uses a set of three potentiometers to control rear fan speed, temperature, and mode settings. The Auxiliary HVAC Control module has inputs for 5V and low Reference that is used by all three potentiometers. There are three signal circuits between each of the potentiometers and the HVAC Control Module.

Auxiliary HVAC Control Module (with RSA)

Auxiliary HVAC Control functions are integrated into the Rear Seat Entertainment Module. The Rear Seat Entertainment Module communicates Rear HVAC settings over serial data.

Auxiliary HVAC Control Functions

All Auxiliary functions and DTCs are handled by the HVAC control module. There are two ways the rear functions can be controlled.

Control from the HVAC control module: If the AUX button on the HVAC control module is pressed, the rear HVAC system will be enabled. The settings for the rear will mimic the Driver settings on the HVAC Control Module.

Control from the auxiliary HVAC control module: If at any time any of the three Auxiliary controls are adjusted, control of the rear HVAC System will transfer to the Auxiliary controls. If the Aux button is not currently enabled, adjusting the Auxiliary controls will enable it, even if the front system is Off.

Auxiliary Mode Actuator

The auxiliary Mode actuator is a 5-wire bi-directional electric motor that incorporates a feedback potentiometer. Low reference, 5-volt reference, position signal, and 2 control circuits enable the actuator to operate. The control circuits use either a 0 or 12-volt value to coordinate the actuator movement. When the actuator is at rest, both control circuits have a value of 0 volts. In order to move the actuator, the HVAC control module grounds one of the control circuits while providing the other with 12 volts. The HVAC control module reverses the polarity of the control circuits to move the actuator in the opposite direction. 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, one of the control circuits is grounded. 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 removes power and ground from the control circuits.

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 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 increases the amount of time that the speed signal is modulated to ground. As the requested blower speed decreases, the auxiliary HVAC control module 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 volts 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

There are 2 separate operator controls for the auxiliary HVAC system. There is the front auxiliary HVAC control assembly and the rear seat audio (RSA) control module. If the front auxiliary blower motor switch is in the AUX. position, then the system will only function with inputs to the front auxiliary HVAC control assembly. If the front auxiliary blower motor switch is in the OFF position, then the RSA control module does not respond to input. The auxiliary HVAC control module can not request A/C operation from the PCM. 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.

Afterblow

Afterblow is a feature that dries the evaporator core by operating the blower motor after the engine is turned off. This reduces the amount of microbial growth that can create undesirable odors. The vehicle does not come equipped with the afterblow feature turned on. If the afterblow feature is required due to an odor concern, it must be turned on by the scan tool.

The following conditions must be met for afterblow to operate

1. The A/C compressor operated during the prior key cycle.
2. The system voltage is at least 11 volts to start and 10 volts to continue to run.
3. The ignition has been in the OFF position for at least 30 minutes.

Once the above conditions have been met the following sequence of events will occur

1. The blower will run for a range of 2 minutes 30 seconds to 4 minutes.
2. The recirculation door moves to outside air position.
3. The mode valve moves to the floor position.

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 a 5-wire bi-directional electric motor that incorporates a feedback potentiometer. Low reference, 5-volt reference, position signal, and 2 control circuits enable the actuator to operate. The control circuits use either a 0 or 12-volt value to coordinate the actuator movement. When the actuator is at rest, both control circuits have a value of 0 volts. In order to move the actuator, the HVAC control module grounds one of the control circuits while providing the other with 12 volts. The HVAC control module reverses the polarity of the control circuits to move the actuator in the opposite direction. 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, one of the control circuits is grounded. 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 removes power and ground from the control circuits.

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.

When the HVAC control module is ON, the air that is delivered to the auxiliary HVAC system is the low auxiliary blower speed. When the operator selects medium blower speed, power is delivered to the auxiliary blower motor through the auxiliary blower motor medium speed control circuit.

When the operator selects high blower speed, power is delivered to the auxiliary blower motor through the auxiliary blower motor high speed control circuit. Ground is provided to the blower motor through the ground circuit. Power and ground are provided to the auxiliary HVAC control module through the ignition 3 voltage and ground circuits.

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

The Auxiliary HVAC Control Module uses a set of three potentiometers to control rear fan speed, temperature, and mode settings. The Auxiliary HVAC Control module has inputs for 5V and low Reference that is used by all three potentiometers. There are three signal circuits between each of the potentiometers and the HVAC Control Module.

Auxiliary HVAC Control functions are integrated into the Rear Seat Entertainment Module. The Rear Seat Entertainment Module communicates Rear HVAC settings over serial data.

All Auxiliary functions and DTCs are handled by the HVAC control module. There are two ways the rear functions can be controlled.

Control from the HVAC control module: If the AUX button on the HVAC control module is pressed, the rear HVAC system will be enabled. The settings for the rear will mimic the Driver settings on the HVAC Control Module.

Control from the auxiliary HVAC control module: If at any time any of the three Auxiliary controls are adjusted, control of the rear HVAC System will transfer to the Auxiliary controls. If the Aux button is not currently enabled, adjusting the Auxiliary controls will enable it, even if the front system is Off.

Air Temperature Actuators

The air temperature actuator is a 5-wire bi-directional electric motor that incorporates a feedback potentiometer. Low reference, 5-volt reference, position signal, and 2 control circuits enable the actuator to operate. The driver air temperature actuator is a reverse polarity motor. The control circuits use either a 0 or 12-volt value to coordinate the actuator movement. When the actuator is at rest, both control circuits have a value of 0 volts. In order to move the actuator, the HVAC control module grounds one of the control circuits while providing the other with 12 volts. The HVAC control module reverses the polarity of the control circuits to move the actuator in the opposite direction. 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, one of the control circuits is grounded. 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 removes power and ground from the control circuits.

Auxiliary Air Temperature Actuator

The auxiliary air temperature actuator is a 5-wire bi-directional electric motor that incorporates a feedback potentiometer. Low reference, 5-volt reference, position signal, and 2 control circuits enable the actuator to operate. The driver air temperature actuator is a reverse polarity motor. The control circuits use either a 0 or 12-volt value to coordinate the actuator movement. When the actuator is at rest, both control circuits have a value of 0 volts. In order to move the actuator, the HVAC control module grounds one of the control circuits while providing the other with 12 volts. The HVAC control module reverses the polarity of the control circuits to move the actuator in the opposite direction. 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, one of the control circuits is grounded. 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 removes power and ground from the control circuits.

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

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.

Ambient Air Temperature Sensor

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. If the ambient air temperature sensor drops below 2°C (35°F) the compressor clutch will be disabled until the ignition is OFF for more than 3 hours or an instant OAT update is performed no matter what the actual temperature is due to the filtered value being used by the HVAC control module. The ambient air temperature value is updated under the following conditions

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).

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.