HVAC System - Automatic: Other Chevrolet Tahoe III

Sensor Resistance Table

Scheme 72

Scheme 73

Scheme 74

Scheme 75

Scheme 76

Scheme 77

Scheme 78

Scheme 79

Scheme 80

Air Temperature Sensors

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

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

A signal and low reference circuit enables the sensor to operate. As the air temperature surrounding the sensor increases, the sensor resistance decreases. The sensor signal voltage decreases as the resistance decreases. The sensor operates within a temperature range between -40 to +101°C (-40 to +215°F). The sensor signal varies between 0-5 volts. The HVAC control module converts the signal to a range between 0-255 counts. As the air temperature increases the count value will decrease. If the HVAC control module or auxiliary HVAC control module detects a malfunctioning sensor, then the control module software will use a defaulted air temperature value. The default value for the 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.

Reference Information

Schematic Reference

HVAC Schematics

Connector End View Reference

Component Connector End Views

Description and Operation

1. «Air Temperature Description and Operation»(ref-364529-S06818200412010063000000)
2. «Air Delivery Description and Operation»(ref-364529-S24392545842010063000000)

Electrical Information Reference

1. «Circuit Testing»(ref-364488-S04114729552010063000000)
2. «Connector Repairs»(ref-364488-S23771656832010063000000)
3. «Testing for Intermittent Conditions and Poor Connections»(ref-364488-S16423338542010063000000)
4. «Wiring Repairs»(ref-364488-S17530456672010063000000)

Scan Tool Reference

Control Module References for scan tool information

Circuit/System Verification

1. 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.
2. Measure actual inside air temperature using a thermometer. Compare this value to the scan tool Inside Air Temp. Sensor parameter and Aux. 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.
3. 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 Sensor Circuit Malfunction.

Repair Procedures

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

1. «Air Temperature Sensor Replacement - Upper Auxiliary»(ref-364529-S08333799042010063000000)
2. «Duct Air Temperature Sensor Replacement - Upper Right Side»(ref-364529-S02951227742010063000000)
3. «Duct Air Temperature Sensor Replacement - Upper Left Side»(ref-364529-S41504267232010063000000)
4. «Air Temperature Sensor Replacement - Lower Auxiliary (Delphi)»(ref-364529-S04274894002010063000000)
5. «Duct Air Temperature Sensor Replacement - Lower Left Side»(ref-364529-S41892303402010063000000)
6. «Duct Air Temperature Sensor Replacement - Lower Right Side»(ref-364529-S25076974652010063000000)
7. «Ambient Air Temperature Sensor Replacement»(ref-364529-S29489482352010063000000)
8. «Inside Air Temperature Sensor Replacement»(ref-364529-S07422060312010063000000)
9. «Auxiliary Inside Air Temperature Sensor Assembly Replacement»(ref-364529-S22817576082010063000000)
10. «Control Module References»(ref-364489-S22329914082010063000000) 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-364529-S06818200412010063000000)
2. «Air Delivery Description and Operation»(ref-364529-S24392545842010063000000)

Electrical Information Reference

1. «Circuit Testing»(ref-364488-S04114729552010063000000)
2. «Connector Repairs»(ref-364488-S23771656832010063000000)
3. «Testing for Intermittent Conditions and Poor Connections»(ref-364488-S16423338542010063000000)
4. «Wiring Repairs»(ref-364488-S17530456672010063000000)

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. «Ambient Light Sensor Replacement»(ref-364469-S02936569682010063000000)
2. «Control Module References»(ref-364489-S22329914082010063000000) 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-364529-S24392545842010063000000)
2. «Air Temperature Description and Operation»(ref-364529-S06818200412010063000000)

Electrical Information Reference

1. «Circuit Testing»(ref-364488-S04114729552010063000000)
2. «Connector Repairs»(ref-364488-S23771656832010063000000)
3. «Testing for Intermittent Conditions and Poor Connections»(ref-364488-S16423338542010063000000)
4. «Wiring Repairs»(ref-364488-S17530456672010063000000)

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-364529-S18883774122010063000000)
2. «Mode Valve Actuator Replacement»(ref-364529-S00139768392010063000000)
3. «Temperature Valve Actuator Replacement - Left Side»(ref-364529-S17902198692010063000000)
4. «Temperature Valve Actuator Replacement - Right Side»(ref-364529-S41092415212010063000000)
5. «Auxiliary Temperature Valve Actuator Replacement (Behr)»(ref-364529-S29190516982010063000000) or «Auxiliary Temperature Valve Actuator Replacement (Delphi)»(ref-364529-S31177069132010063000000)
6. «Auxiliary Mode Valve Actuator Replacement (Behr)»(ref-364529-S06342419872010063000000) or «Auxiliary Mode Valve Actuator Replacement (Delphi)»(ref-364529-S22847448432010063000000)
7. «Control Module References»(ref-364489-S22329914082010063000000) for HVAC control module replacement, setup, and programming

1. Reprogram the HVAC control module that set DTC B1023. 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 for control module replacement, setup, and programming

Schematic Reference

Hybrid Cooling Schematics

Connector End View Reference

Component Connector End Views

Description and Operation

Air Delivery Description and Operation

Electrical Information Reference

1. «Circuit Testing»(ref-364488-S04114729552010063000000)
2. «Connector Repairs»(ref-364488-S23771656832010063000000)
3. «Testing for Intermittent Conditions and Poor Connections»(ref-364488-S16423338542010063000000)
4. «Wiring Repairs»(ref-364488-S17530456672010063000000)

Scan Tool Reference

Control Module References for scan tool information

1. Ignition ON, command the heater core pump ON and OFF with a scan tool.
2. Observe the operation of heater core pump.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

1. «Control Module References»(ref-364489-S22329914082010063000000) for HVAC control module replacement, setup, and programming
2. «Heater Coolant Pump Replacement (HP2)»(ref-364481-S05606120272010063000000)

Schematic Reference

HVAC Schematics HVAC Schematics

Connector End View Reference

Component Connector End Views Component Connector End Views

Description and Operation

1. «Air Temperature Description and Operation»(ref-364529-S06818200412010063000000) Air Temperature Description and Operation
2. «Air Delivery Description and Operation»(ref-364529-S24392545842010063000000) Air Delivery Description and Operation

Electrical Information Reference

1. «Circuit Testing»(ref-364488-S04114729552010063000000) Circuit Testing
2. «Connector Repairs»(ref-364488-S23771656832010063000000) Connector Repairs
3. «Testing for Intermittent Conditions and Poor Connections»(ref-364488-S16423338542010063000000) Testing for Intermittent Conditions and Poor Connections
4. «Wiring Repairs»(ref-364488-S17530456672010063000000) Wiring Repairs

Scan Tool Reference

Control Module References 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 Diagnostic Repair Verification after completing the diagnostic procedure.

1. «Air Conditioning Refrigerant Temperature Sensor Replacement»(ref-364529-S15205068632010063000000) Evaporator Air Temperature Sensor Replacement
2. «Control Module References»(ref-364489-S22329914082010063000000) Control Module References 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-364529-S06818200412010063000000)
2. «Air Delivery Description and Operation»(ref-364529-S24392545842010063000000)

Electrical Information Reference

1. «Circuit Testing»(ref-364488-S04114729552010063000000)
2. «Connector Repairs»(ref-364488-S23771656832010063000000)
3. «Testing for Intermittent Conditions and Poor Connections»(ref-364488-S16423338542010063000000)
4. «Wiring Repairs»(ref-364488-S17530456672010063000000)

Scan Tool Reference

Control Module References for scan tool information

Ignition ON, observe the scan tool A/C Pressure Sensor parameter. The reading should be between 14.96 kPa and 3295 kPa 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 (Non-HP2)»(ref-364481-S34538316772010063000000) or «Air Conditioning (A/C) Refrigerant Pressure Sensor Replacement (HP2)»(ref-364481-S42616292722010063000000)
2. «Control Module References»(ref-364489-S22329914082010063000000) 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-364529-S24392545842010063000000)
2. «Air Temperature Description and Operation»(ref-364529-S06818200412010063000000)

Electrical Information Reference

1. «Circuit Testing»(ref-364488-S04114729552010063000000)
2. «Connector Repairs»(ref-364488-S23771656832010063000000)
3. «Testing for Intermittent Conditions and Poor Connections»(ref-364488-S16423338542010063000000)
4. «Wiring Repairs»(ref-364488-S17530456672010063000000)

Scan Tool Reference

Control Module References for scan tool information

Ignition ON, command the A/C Relay ON and OFF with a scan tool. Feel/listen for the A/C relay to click.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

1. «Relay Replacement (Attached to Wire Harness)»(ref-364493-S18150273522010063000000) or «Relay Replacement (Within an Electrical Center)»(ref-364493-S12240576782010063000000)
2. «Control Module References»(ref-364489-S22329914082010063000000) for 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-364529-S24392545842010063000000)
2. «Air Temperature Description and Operation»(ref-364529-S06818200412010063000000)

Electrical Information Reference

1. «Circuit Testing»(ref-364488-S04114729552010063000000)
2. «Connector Repairs»(ref-364488-S23771656832010063000000)
3. «Testing for Intermittent Conditions and Poor Connections»(ref-364488-S16423338542010063000000)
4. «Wiring Repairs»(ref-364488-S17530456672010063000000)

Scan Tool Reference

Control Module References for scan tool information

Ignition ON, observe the scan tool Low Pressure Switch parameter. The parameter should read closed.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

1. «Air Conditioning (A/C) Refrigerant Pressure Sensor Replacement (Non-HP2)»(ref-364481-S34538316772010063000000) or «Air Conditioning (A/C) Refrigerant Pressure Sensor Replacement (HP2)»(ref-364481-S42616292722010063000000)
2. «Control Module References»(ref-364489-S22329914082010063000000) for the HVAC control module 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-364529-S06818200412010063000000)
2. «Air Delivery Description and Operation»(ref-364529-S24392545842010063000000)

Electrical Information Reference

1. «Circuit Testing»(ref-364488-S04114729552010063000000)
2. «Connector Repairs»(ref-364488-S23771656832010063000000)
3. «Testing for Intermittent Conditions and Poor Connections»(ref-364488-S16423338542010063000000)
4. «Wiring Repairs»(ref-364488-S17530456672010063000000)

Scan Tool Reference

Control Module References for scan tool information

1. Engine running, press the A/C request switch. The A/C compressor clutch should engage.
2. Place the mode switch in the defrost position. The A/C compressor clutch should engage. If the clutch does not engage refer to «Air Conditioning (A/C) System Performance Test (HP2)»(ref-364481-S02808229742010063000000) or «Air Conditioning (A/C) System Performance Test (Long Wheel Base 1500)»(ref-364481-S04983510062010063000000) or «Air Conditioning (A/C) System Performance Test (Long Wheel Base 2500)»(ref-364481-S13916553082010063000000) or «Air Conditioning (A/C) System Performance Test (Short Wheel Base)»(ref-364481-S34482729292010063000000) .

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

1. «Air Conditioning Compressor Replacement (HP2)»(ref-364481-S08835530192010063000000) or «Air Conditioning Compressor Replacement (LY2, LY5, LH6, L76, L92 and LMG)»(ref-364481-S12997893232010063000000)
2. «Air Conditioning Cycling Switch Replacement (HP2)»(ref-364481-S20654392652010063000000) or «Air Conditioning Cycling Switch Replacement (Non-HP2)»(ref-364481-S24553541512010063000000)
3. «Control Module References»(ref-364489-S22329914082010063000000) for HVAC control module or ECM 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-364529-S06818200412010063000000)
2. «Air Delivery Description and Operation»(ref-364529-S24392545842010063000000)

Electrical Information Reference

1. «Circuit Testing»(ref-364488-S04114729552010063000000)
2. «Connector Repairs»(ref-364488-S23771656832010063000000)
3. «Testing for Intermittent Conditions and Poor Connections»(ref-364488-S16423338542010063000000)
4. «Wiring Repairs»(ref-364488-S17530456672010063000000)

Scan Tool Reference

Control Module References for scan tool information

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

1. «Blower Motor Control Module Replacement»(ref-364481-S08577666542010063000000)
2. «Blower Motor Replacement»(ref-364481-S10171369992010063000000)
3. «Control Module References»(ref-364489-S22329914082010063000000) for ECM 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-364529-S24392545842010063000000)
2. «Air Temperature Description and Operation»(ref-364529-S06818200412010063000000)

Electrical Information Reference

1. «Circuit Testing»(ref-364488-S04114729552010063000000)
2. «Connector Repairs»(ref-364488-S23771656832010063000000)
3. «Testing for Intermittent Conditions and Poor Connections»(ref-364488-S16423338542010063000000)
4. «Wiring Repairs»(ref-364488-S17530456672010063000000)

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 Control Module Replacement»(ref-364481-S27896843452010063000000)
2. «Auxiliary Blower Motor Replacement (Standard Wheelbase)»(ref-364481-S02135555242010063000000) or «Auxiliary Blower Motor Replacement (Extended Wheelbase)»(ref-364481-S13889786542010063000000)
3. «Control Module References»(ref-364489-S22329914082010063000000) 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-364529-S24392545842010063000000)
2. «Air Temperature Description and Operation»(ref-364529-S06818200412010063000000)

Electrical Information Reference

1. «Circuit Testing»(ref-364488-S04114729552010063000000)
2. «Connector Repairs»(ref-364488-S23771656832010063000000)
3. «Testing for Intermittent Conditions and Poor Connections»(ref-364488-S16423338542010063000000)
4. «Wiring Repairs»(ref-364488-S17530456672010063000000)

Scan Tool Reference

Control Module References for scan tool information

Note. Check for bulletins before proceeding.

1. Ignition ON, place the blower motor switch in each speed position. Verify that the blower motor operates properly in each position. If the blower motor does not operate properly in all speeds, refer to «Blower Motor Malfunction»(ref-364529-S23025047132010063000000) .
2. Using the scan tool observe the mode, temperature and recirculation door positions. Verify the actual and commanded door positions are within 4 counts of each other. If not within the specified range, refer to Circuit/System Testing «DTC B0228, B0413, B0423, B0433, B3779, or B3782»(ref-364529-S41488664452010063000000) .
3. Engine ON, A/C ON, place the temperature control in the coldest position. Verify that the A/C compressor clutch engages. If the A/C compressor clutch does not engage, refer to «Air Conditioning Compressor Malfunction»(ref-364529-S28284283032010063000000) . If the A/C compressor is engaged, but air is insufficiently cooled. Refer to «Air Conditioning (A/C) System Performance Test (HP2)»(ref-364481-S02808229742010063000000) or «Air Conditioning (A/C) System Performance Test (Long Wheel Base 1500)»(ref-364481-S04983510062010063000000) or «Air Conditioning (A/C) System Performance Test (Long Wheel Base 2500)»(ref-364481-S13916553082010063000000) or «Air Conditioning (A/C) System Performance Test (Short Wheel Base)»(ref-364481-S34482729292010063000000) .
4. Turn the A/C OFF and place the temperature control in the warmest position. If the air is insufficiently heated refer to «Heating Performance Diagnostic»(ref-364481-S32805237752010063000000) .
5. Engine OFF, 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.
6. 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 Air Temperature Sensor Circuit Malfunction.
7. Measure actual inside air temperature using a thermometer. Compare this value to the scan tool Inside Air Temp. Sensor parameter and Aux. Inside Air Temp. parameter. The measured temperature should be within 5 degrees of parameter. If not within the specified range, refer to Inside Air Temperature Sensor Circuit Malfunction.
8. 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 Sensor Circuit Malfunction.
9. 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. If not within the specified range, refer to Evaporator Air Temperature Sensor Circuit Malfunction.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

1. «Duct Air Temperature Sensor Replacement - Lower Left Side»(ref-364529-S41892303402010063000000)
2. «Duct Air Temperature Sensor Replacement - Lower Right Side»(ref-364529-S25076974652010063000000)
3. «Duct Air Temperature Sensor Replacement - Upper Left Side»(ref-364529-S41504267232010063000000)
4. «Duct Air Temperature Sensor Replacement - Lower Left Side»(ref-364529-S41892303402010063000000)
5. «Air Temperature Sensor Replacement - Lower Auxiliary (Delphi)»(ref-364529-S04274894002010063000000)
6. «Auxiliary Inside Air Temperature Sensor Assembly Replacement»(ref-364529-S22817576082010063000000)
7. «Air Temperature Sensor Replacement - Upper Auxiliary»(ref-364529-S08333799042010063000000)
8. «Air Conditioning Refrigerant Temperature Sensor Replacement»(ref-364529-S15205068632010063000000)
9. «Ambient Air Temperature Sensor Replacement»(ref-364529-S29489482352010063000000)
10. «Ambient Light Sensor Replacement»(ref-364469-S02936569682010063000000)
11. «Control Module References»(ref-364489-S22329914082010063000000)

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 81

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Scheme 84

Scheme 85

Scheme 86

Scheme 87

Scheme 88

Scheme 89

Scheme 90

Scheme 91

Scheme 92

Scheme 93

Scheme 94

Scheme 95

Scheme 96

Scheme 97

Scheme 98

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

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 auxiliary HVAC system will be enabled. The settings for the auxiliary 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.

Mode Actuator

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

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

Auxiliary Mode Actuator

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

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

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

Blower Motor Control Processor

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

Auxiliary Blower Motor Control Processor

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

Air Speed - Front Control

The blower control switch is integrated into the HVAC control module. The 2 rocker type switches provide the vehicle operator the ability to select several blower speeds. The HVAC control module uses a bar graph type display to indicate the selected blower speed. The blower motor control processor supplies a 5-volt reference to the HVAC control module on the blower motor speed control circuit. The blower motor control module is an interface between the HVAC control module and the blower motor. The blower motor speed control, battery positive and ground circuits enable the control module to operate. The HVAC control module provides a variable voltage to the blower motor control module to request the selected blower speed. The blower motor control module provides a pulse width modulation (PWM) signal to the blower motor in order to control the blower motor speed. The module supplies 12 volts to the blower motor through the blower motor voltage supply circuit. When the HVAC control module is operating in AUTO mode, the system automatically controls the blower speed. If an OnStar® call is initiated while the blower is in the high speed position the blower speed will be lowered to reduce background noise.

Air Speed - Auxiliary

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

Air Distribution

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

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

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

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.

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 4°C (40°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 23°C (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 23°C (74°F) setpoint, auto blower, auto mode, rear in mimic.
3. In hot ambient, the system uses 23°C (74°F) setpoint (16°C (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.

Heater Core Coolant Pump

The primary purpose of the heater core coolant pump is to circulate engine coolant through the HVAC heater core when heat is required in the cabin for comfort. This normally happens when the vehicle is in an Auto Stop and the mechanical pump is not spinning. If the HVAC control module has determined heat is needed for the cabin, this pump is turned on once the engine is shut off so the customer does not notice a change in heater duct discharge temperatures. The HVAC control module controls the auxiliary coolant pump relay via the heater core coolant pump relay control circuit. Heater core coolant pump relay supplies voltage to the heater core coolant pump.

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

Auxiliary HVAC Control Module

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

Rear Seat Audio Control Module

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

Air Temperature Actuator

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

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

Auxiliary Air Temperature Actuator

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

Air Temperature Sensor

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

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

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

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

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

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

Evaporator Temperature Sensor

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

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.

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. 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.