HVAC System - Automatic Cadillac STS I

Fastener Tightening Specifications

Fastener Tightening Specifications

HVAC Schematic Icons

HVAC Schematic Icons Icon Icon Definition CAUTION: When performing service on or near the SIR components or the SIR wiring, the SIR system must be disabled. Refer to SIR Disabling and Enabling Zones. Failure to observe the correct procedure could cause deployment of the SIR components, personal injury, or unnecessary SIR system repairs

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HVAC Connector End Views

A/C Compressor Clutch Connector End Connector Part Information OEM: 7282-5548-30 Service: 2-Way M YESC Weather Pack (BLK) Terminal Part Information Terminal: Terminal Seal: Release Tool: Core Crimp: Insulation Crimp: Test Probe: Pin Wire Color Circuit No. Function 1 D-GN 59 A/C Compressor Clutch Supply Voltage 2 BK 1550 Ground (LH2) BK 1450 Ground (LY7)

A/C Refrigerant Pressure Sensor Connector End Connector Part Information OEM: 12065287 Service: 12102748 3-Way F Metri-Pack 150 Series (BK) Terminal Part Information Terminal: Terminal Seal: Release Tool: Core Crimp: Insulation Crimp: Test Probe: Pin Wire Color Circuit No. Function A BK/WH 2751 Signal Ground (LH2) BK 452 Sensor Low Reference (LY7) B GY 2700 A/C Pressure Sensor 5-Volt Reference (LH2) GY 596 5-Volt Reference (LY7) C OG/BK 380 A/C Refrigerant Pressure Sensor Signal (LH2) RD/BK 380 A/C Refrigerant Pressure Sensor Signal (LY7)

Air Quality Sensor Connector End (K14) Connector Part Information OEM: 7283-7062-40 Service: 6-Way F 090-2/Class 3 (WH) Terminal Part Information Terminal: Terminal Seal: Release Tool: Core Crimp: Insulation Crimp: Test Probe: Pin Wire Color Circuit No. Function 1 YE 61 Outside Ambient Temperature Sensor Low Reference 2 PU/WH 5203 Air Quality HC Sensor Signal 3 PK 1439 Run/Crank Ignition 1 Voltage 4 L-GN/WH 6845 Air Quality NOX Sensor Signal 5 - - Not Used 6 BK 250 Ground

Air Temperature Actuator - Driver Connector End Connector Part Information 7283-5830-30 5 Way F Yazaki (BK) Terminal Part Information Terminal: Terminal Seal: Release Tool: Core Crimp: Insulation Crimp: Test Probe: Pin Wire Color Circuit No. Function 1 YE 61 Low Reference 2 GY 705 5-Volt Reference 3 L-BU 733 Driver Air Temperature Door Position Signal 4 D-BU 1199 Driver Air Temperature Door Control B 5 RD 1791 Driver Air Temperature Door Control A

Air Temperature Actuator - Front Passenger Connector End Connector Part Information 7283-5830-30 5 Way F Yazaki (BK) Terminal Part Information Terminal: Terminal Seal: Release Tool: Core Crimp: Insulation Crimp: Test Probe: Pin Wire Color Circuit No. Function 1 GY 705 5-Volt Reference 2 YE 61 Low Reference 3 D-BU 1646 Passenger Air Temperature Door Position Signal 4 WH/BK 1236 Passenger Air Temperature Door Control B 5 GY/BK 2778 Passenger Air Temperature Door Control A

Air Temperature Actuator - Rear Passenger Connector End Connector Part Information 7283-5830-30 5 Way F Yazaki (BK) Terminal Part Information Terminal: Terminal Seal: Release Tool: Core Crimp: Insulation Crimp: Test Probe: Pin Wire Color Circuit No. Function 1 YE 61 Low Reference 2 GY 705 5-Volt Reference 3 D-GN 2600 Rear Passenger Air Temperature Door Position Signal 4 BN 2775 Rear Passenger Air Temperature Door Control B 5 L-BU 2776 Rear Passenger Air Temperature Door Control A

Air Temperature Sensor - Inside Connector End Connector Part Information OEM: 72831020 Service: 2-Way F Yazaki 2.3 Series (WH) Terminal Part Information Terminal: Terminal Seal: Release Tool: Core Crimp: Insulation Crimp: Test Probe: Pin Wire Color Circuit No. Function 1 YE 61 Outside Ambient Temperature Sensor Low Reference 2 D-GN 734 Inside Air Temperature Sensor Signal

Ambient Air Temperature Sensor Connector End Connector Part Information OEM: 12052642 Service: 12101856 2-Way F Metri-Pack 150 Series Sealed (L-GN) Terminal Part Information Terminal: Terminal Seal: Release Tool: Core Crimp: Insulation Crimp: Test Probe: Pin Wire Color Circuit No. Function A L-GN/BK 735 Outside Ambient Air Temperature Sensor Signal B YE 61 Outside Ambient Temperature Sensor Low Reference

Blower Controller Connector End Connector Part Information OEM: 60981449 Service: 4-Way F 312 Sumi Tomo (BK) Terminal Part Information Terminal: Terminal Seal: Release Tool: Core Crimp: Insulation Crimp: Test Probe: Pin Wire Color Circuit No. Function 1 BK 450 Ground 2 GY/BK 754 Blower Motor Speed Control 3 L-BU 188 Blower Motor Resistor Assembly Supply Voltage 4 PU 374 Blower Motor Fan Control

Blower Motor Connector End Connector Part Information OEM: 7283302030 Service: 2-Way F 312/Class 2 (BK) Terminal Part Information Terminal: Terminal Seal: Release Tool: Core Crimp: Insulation Crimp: Test Probe: Pin Wire Color Circuit No. Function 1 L-BU 188 Blower Motor Resistor Assembly Supply Voltage 2 PU 374 Blower Motor Fan Control

Evaporator Temperature Sensor Connector End Connector Part Information OEM: 7123-2820 Service: 2-Way F Yazaki (CL) Terminal Part Information Terminal: Terminal Seal: Release Tool: Core Crimp: Insulation Crimp: Test Probe: Pin Wire Color Circuit No. Function 1 GY 731 A/C Refrigerant Low Temperature Sensor Signal 2 YE 61 Low Reference

HVAC Control Module - C1 Connector End Connector Part Information OEM: 12160778 Service: 12160778 24-Way F Micro-Pack 100 Series (BN) Terminal Part Information Terminal: Terminal Seal: Release Tool: Core Crimp: Insulation Crimp: Test Probe: Pin Wire Color Circuit No. Function A1 RD/WH 340 Battery Positive Voltage A2 YE 6817 LED Backlight Dimming Control A2 YE 6817 LED Backlight Dimming Control A3 - - Not Used A4 L-GN 1478 Coolant Level Switch Signal A5 BN 247 Medium Blower Motor Control A6 - - Not Used A7 PU/WH 5203 Air Quality HC Sensor Signal A8 L-GN/BK 735 Outside Ambient Air Temperature Sensor Signal A9 GY 731 A/C Refrigerant Low Temperature Sensor Signal A10 L-BU/BK 590 Solar Sensor Driver Signal A11 WH 278 Ambient Light Sensor Signal A12 GY 705 5-Volt Reference B1 PK 1539 Run/Crank Ignition 1 Voltage B2-B4 - - Not Used B5 D-GN 5060 Low Speed GMLAN Serial Data B6 GY/BK 754 Blower Motor Speed Control B7 L-GN/WH 6845 Air Quality NOX Sensor Signal B8 - - Not Used B9 D-GN 734 Inside Air Temperature Sensor Signal B10 GY 1548 Passenger Solar Sensor Signal B11 BK/WH 451 Ground B12 YE 61 Outside Ambient Temperature Sensor Low Reference

HVAC Control Module - C2 Connector End Connector Part Information OEM: CO12110088 Service: 24-Way F Micro-Pack 100 Series (GY) Terminal Part Information Terminal: Terminal Seal: Release Tool: Core Crimp: Insulation Crimp: Test Probe: Pin Wire Color Circuit No. Function A1 L-BU 733 Air Temperature Door Position Signal A2 YE/BK 1814 Lower Mode Door Position Signal A3 BN 41 Run Ignition 3 Voltage A4 GY 2599 Rear Mode Door Position Signal A5 - - Not Used A6 L-BU 5517 Passenger Compartment Rear Air Temperature Sensor Low Reference A7 L-GN/WH 5729 Rear Mode Door Control A A8 YE 1791 Air Temperature Door Control Low Reference A9 GY/BK 2778 Passenger Air Temperature Motor Control A10 YE 1318 Lower Mode Door Control A11 GY 5127 After Boil Coolant Pump Relay Control A12 PU 1838 Recirculation Door Position Signal B1 D-BU 1646 Passenger Air Temperature Door Position Signal B2 - - Not Used B3 D-GN 5518 Passenger Compartment Rear Air Temperature Sensor Signal B4 PU 722 Rear Mode Switch Signal (w/KA6) B5 L-BU 733 Rear Temperature Switch Signal (w/KA6) B6 BN 5516 Passenger Compartment Rear Air Temperature Motor Control B7 L-GN/BK 5730 Rear Mode Door Control B B8 D-BU 1199 Air Temperature Door Control B9 WH/BK 1236 Passenger Air Temperature Door Control B10 TN 2273 Mode Door Control B11 - - Not Used B12 D-GN 1614 Recirculation Door Control

HVAC Control Module - Rear Auxiliary Connector End (w/KA6) Connector Part Information OEM: CA12084944 Service: 16-Way F Micro-Pack 100 (BK) Terminal Part Information Terminal: Terminal Seal: Release Tool: Core Crimp: Insulation Crimp: Test Probe: Pin Wire Color Circuit No. Function A1 YE 1491 Backlight Lamp Control A2 PK 1636 Right Rear Heated Seat Low Indicator Control A3 D-BU/WH 6586 Right Rear Heated Seat Medium Indicator Control A4 TN/WH 1635 Right Rear Heated Seat High Indicator Control A5 YE 182 Heated Seat Control Module Enable Signal A6 BN 1637 Left Rear Heated Seat Switch Signal A7 L-BU 733 Rear Temperature Switch Signal A8 YE 61 Low Reference B1 BK 450 Ground B2 TN/WH 1638 Left Rear Heated Seat High Indicator Control B3 BN/WH 6585 Left Rear Heated Seat Medium Indicator Control B4 PK 1631 Left Rear Heated Seat Low Indicator Control B5 BN 1634 Right Rear Heated Seat Switch Signal B6 PU 722 Rear Mode Switch Signa; B7 GY 705 5-Volt Reference B8 - - Not Used

Mode Actuator Connector End Connector Part Information 7283-5830-30 5 Way F Yazaki (BK) Terminal Part Information Terminal: Terminal Seal: Release Tool: Core Crimp: Insulation Crimp: Test Probe: Pin Wire Color Circuit No. Function 1 GY 705 5-Volt Reference 2 YE 61 Low Reference 3 YE/BK 1814 Mode Door Position Signal 4 OR 2273 Mode Door Control A 5 YE/GN 1318 Mode Door Control B

Mode Actuator - Auxiliary Connector End Connector Part Information OEM: 7283-5830-30 Service: 5-Way F Yazaki (BK) Terminal Part Information Terminal: Terminal Seal: Release Tool: Core Crimp: Insulation Crimp: Test Probe: Pin Wire Color Circuit No. Function 1 YE 61 Outside Ambient Temperature Sensor Low Reference 2 GY 705 5-Volt Reference 3 GY 2599 Rear Mode Motor Signal 4 L-GN/WH 5729 Rear Mode Motor Supply Voltage 5 L-GN/BK 5730 Rear Mode Motor Low Reference

Recirculation Actuator Connector End Connector Part Information OEM: 7283-5830-30 Service: 5-Way F Yazaki (BK) Terminal Part Information Terminal: Terminal Seal: Release Tool: Core Crimp: Insulation Crimp: Test Probe: Pin Wire Color Circuit No. Function 1 YE 61 Outside Ambient Temperature Sensor Low Reference 2 GY 705 5-Volt Reference 3 BN 41 Run Ignition 3 Voltage 4 PU 1838 Recirculation Door Position Signal 5 D-GN 1614 Recirculation Door Control

Sunload Sensor Connector End Connector Part Information OEM: 12064760 Service: 4-Way F Metri-Pack 150 Series (BK) Terminal Part Information Terminal: Terminal Seal: Release Tool: Core Crimp: Insulation Crimp: Test Probe: Pin Wire Color Circuit No. Function A L-BU/BK 590 Solar Sensor Driver Signal B GY 1548 Passenger Solar Sensor Signal C YE 61 Low Reference D WH 278 Ambient Light Sensor Signal

Scan Tool Output Controls

HVAC Control Module Scan Tool Output Controls

ECM Scan Tool Output Controls

Scan Tool Data List

HVAC Control Module Scan Tool Data List

ECM Scan Tool Data List

Circuit Description

The ambient air temperature sensor provides the HVAC control module software with the temperature of the air outside the vehicle. That temperature can be displayed in the driver information center (DIC). A reference voltage is supplied to the sensor thermistor and the HVAC control module determines the voltage drop across that device which is proportional to temperature. As the air temperature increases, the resistance decreases and the voltage signal decreases. As the air temperature decreases, the resistance increases and the voltage signal increases. The inside air temperature sensor provides the HVAC control module with the temperature of the air drawn through an aspirator from the passenger compartment across a sensor. A reference voltage is supplied to the sensor thermistor and the HVAC control module determines the voltage drop across that device which is proportional to temperature. As the air temperature increases, the resistance decreases and the voltage signal decreases. As the air temperature decreases, the resistance increases and the voltage signal increases.

DTC Descriptors

This diagnostic procedure supports the following DTCs

1. DTC B0158 Outside Air Temperature Sensor Circuit.
2. DTC B0163 Passenger Compartment Temperature Sensor Circuit.

This vehicle has DTCs which include DTC Symptoms. For more information on DTC Symptoms, refer to DTC Symptom Description in Vehicle DTC Information.

DTC B0158 or B0163

Conditions for Running the DTC

The ignition is turned ON.

DTC B0158

The HVAC control module detects the ambient air temperature sensor signal circuit is less than 2 counts for more than 30 seconds or more than 253 counts for more than 30 seconds.

DTC B0163

The HVAC control module detects the inside air temperature sensor signal circuit is less than 2 counts or more than 253 counts for 30 seconds.

Action Taken When the DTC Sets

1. The DIC will display 15°C (59°F) for outside air temperature.
2. The DIC will display SERVICE A/C SYSTEM.

The system operates using a default value.

The system operates using a default value.

Conditions for Clearing the DTC

1. The DTC will become history if the HVAC control module no longer detects the condition that set the DTC.
2. The history DTC will clear after 50 fault-free ignition cycles.
3. The DTC can be cleared with a scan tool.

Test Description

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

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

DTC B0158 or B0163

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

1. Solar Load Sensor 1 Circuit refers to the left sunload sensor
2. Solar Load Sensor 2 Circuit refers to the right sunload sensor

This diagnostic procedure supports the following DTCs

1. DTC B0183 Solar Load Sensor 1 Circuit
2. DTC B0188 Solar Load Sensor 2 Circuit

This vehicle has DTCs which include DTC Symptoms. For more information on DTC Symptoms, refer to DTC Symptom Description in Vehicle DTC Information.

DTC B0183 or B0188

The ignition is turned ON.

Conditions for Setting the DTC

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

1. If the DTC is set the system will act as if no sunload condition exists.
2. The driver information center (DIC) will display SERVICE A/C SYSTEM.

1. The DTC will become history if the HVAC control module no longer detects a failure.
2. The history DTC will clear after 50 fault-free ignition cycles.
3. The DTC can be cleared with a scan tool.

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

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

DTC B0183 or B0188

The HVAC door actuator is an electronic motor with a feedback potentiometer. The HVAC control module supplies power and ground to the actuator. The HVAC control module controls the direction of the actuator by changing the polarity of the control circuit. When the actuator reaches the desired position, voltage is removed from the control circuit. The HVAC control module determines the current position of the actuator by monitoring the feedback voltage of the door position signal circuit. The feedback potentiometer position is a function of the actuator position.

1. Air flow control 3 circuit refers to the front mode actuator
2. Air flow control 7 circuit refers to the recirc actuator.
3. Temperature control 1 circuit refers to the driver air temperature actuator
4. Temperature control 2 circuit refers to the passenger air temperature actuator
5. Temperature control 3 circuit refers to the rear air temperature actuator
6. Air flow control 10 circuit refers to the rear mode actuator

This diagnostic procedure supports the following DTCs

1. DTC B0248 Air Flow Control 3 Circuit
2. DTC B0268 Air Flow Control 7 Circuit
3. DTC B0408 Temperature Control 1 Circuit
4. DTC B0418 Temperature Control 2 Circuit
5. DTC B0428 Temperature Control 3 Circuit
6. DTC B3531 Air Flow Control 10 Circuit

This vehicle has DTCs which include DTC Symptoms. For more information on DTC Symptoms, refer to DTC Symptom Description in Vehicle DTC Information.

DTC B0248, B0268, B0408, B0418, B0428, or B3531

1. The ignition is ON.
2. Ignition voltage is between 9-16 volts.

The actuator door movement is restricted or the actual door position differs from the commanded door position by 4 counts or greater for more than 16 seconds.

The HVAC control module will not command actuator movement past the point where the stall condition is detected and will continue to make use of the remaining nonrestricted range.

1. The DTC will become history if the HVAC control module no longer detects the condition that set the DTC.
2. The history DTC will clear after 50 fault-free ignition cycles.
3. The DTC can be cleared with a scan tool.

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

1. 4: This step verifies that the HVAC control module is able to command the appropriate HVAC actuator.

DTC B0248, B0268, B0408, B0418, B0428, or B3531

The HVAC control module controls the HVAC door actuators to regulate the airflow through the HVAC system. Each actuator consists of an electric motor and a potentiometer. The potentiometer inside the door actuator allows the module to monitor the current position of the actuator drive shaft. The module supplies a 5-volt source voltage to the potentiometer on the 5-volt reference circuit. The module supplies ground to the potentiometer through the low reference circuit. The HVAC control module monitors the voltage drop across the potentiometer on the door position signal circuit. When the actuator shaft rotates, the voltage on the door position signal circuit changes.

1. Temperature control 1 Feedback circuit refers to the driver air temperature actuator
2. Temperature control 2 Feedback circuit refers to the passenger air temperature actuator
3. Temperature control 3 Feedback circuit refers to the rear air temperature actuator
4. Air flow control 3 Feedback circuit refers to the front mode actuator
5. Air flow control 7 Feedback circuit refers to the recirc actuator.
6. Air flow control 10 Feedback circuit refers to the rear mode actuator

This diagnostic procedure supports the following DTCs

1. DTC B0413 Temperature Control 1 Feedback Circuit
2. DTC B0423 Temperature Control 2 Feedback Circuit
3. DTC B0433 Temperature Control 3 Feedback Circuit
4. DTC B3761 Air Flow Control 3 Feedback Circuit
5. DTC B3773 Air Flow Control 7 Feedback Circuit
6. DTC B3782 Air Flow Control 10 Feedback Circuit

This vehicle has DTCs which include DTC Symptoms. For more information on DTC Symptoms, refer to DTC Symptom Description in Vehicle DTC Information.

DTC B0413, B0423, B0433, B3761, B3773, or B3782

The ignition is turned ON.

The HVAC control module detects the door position signal circuit is less than 7 counts or greater than 250 counts for 1 minute.

The HVAC control module uses only the minimum and maximum door positions.

1. The DTC becomes history when the HVAC control module no longer detects the condition that set the DTC.
2. The history DTC will clear after 50 fault-free ignition cycles.
3. The DTC can be cleared with a scan tool.

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

1. 4: This step verifies that the HVAC control module is able to command the appropriate HVAC actuator.

DTC B0413, B0423, B0433, B3761, B3773, or B3782

The HVAC control module monitors the outside air quality via the air quality sensor assembly while in AUTO mode. The air quality sensor is a 5-wire sensor, 1 ignition voltage circuit, 2 ground circuits and 2 control circuits. There are 2 sensors inside the air quality sensor assembly. A hydro carbon (HC) sensor which is used for detecting gasoline exhaust fumes and a Nox sensor which is used for detecting nitrous oxide, diesel exhaust fumes. When high levels of hydro carbons (HC) are detected at the front of the vehicle the HC sensor resistance and signal voltage are low. When high levels of Nox are detected at the front of the vehicle the Nox sensor resistance and signal voltage are high.

This diagnostic procedure supports the following DTCs

1. DTC B2496 Nox Sensor Circuit (Outside Air Quality Sensor 2 Circuit)
2. DTC B3843 Hydro Carbon Sensor Circuit (Outside Air Quality Sensor 1 Circuit)

This vehicle has DTCs which include DTC Symptoms. For more information on DTC Symptoms, refer to DTC Symptom Description in Vehicle DTC Information.

DTC B2496 or B3843

The ignition is turned ON.

The HVAC control module detects the air quality sensor signal circuit is less than 0.09 volt (5 counts).

The driver information center (DIC) will display SERVICE A/C SYSTEM.

1. The DTC will become history if the HVAC control module no longer detects a failure.
2. The history DTC will clear after 50 fault-free ignition cycles.
3. The DTC can be cleared with a scan tool.

Diagnostic Aids

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

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

1. 3: Tests for the proper operation of the circuit in the low voltage range.
2. 4: Tests for the proper operation of the circuit in the high voltage range. If the fuse in the jumper opens when you perform this test, the signal circuit is shorted to ground.
3. 5: Tests for a short to voltage in the 5-volt reference circuit.

DTC B2496 or B3843

The HVAC control module monitors the evaporator temperature via the evaporator temperature sensor. When the air is cold, the sensor resistance and signal voltage are high. When the air is warm, the sensor resistance and signal voltage are low.

This diagnostic procedure supports the following DTCs

1. DTC B3933 Evaporator Temperature Sensor Circuit
2. DTC P1531 Air Conditioning (A/C) Evaporator Temperature Sensor Circuit

This vehicle has DTCs which include DTC Symptoms. For more information on DTC Symptoms, refer to DTC Symptom Description in Vehicle DTC Information.

DTC B3933

The ignition is turned ON.

The HVAC control module detects the evaporator temperature sensor signal circuit is less than 0.09 volt (5 counts) or greater than 4.90 volts (250 counts).

1. The driver information center (DIC) will display SERVICE A/C SYSTEM.
2. The A/C OFF segment will illuminate on the HVAC control module.
3. The A/C compressor will be disabled.

1. The DTC will become history if the HVAC control module no longer detects a failure.
2. The history DTC will clear after 50 fault-free ignition cycles.
3. The DTC can be cleared with a scan tool.

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

1. 3: This step tests for the proper operation of the circuit in the high voltage range.
2. 4: This step tests for the proper operation of the circuit in the low voltage range. If the fuse in the jumper opens upon performing this test, the signal circuit has a short to voltage.

DTC B3933

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

This diagnostic procedure supports the following DTCs

1. DTC P0531 Air Conditioning (A/C) Refrigerant Pressure Sensor Circuit
2. DTC P0532 Air Conditioning (A/C) Refrigerant Pressure Sensor Circuit Low Voltage
3. DTC P0533 Air Conditioning (A/C) Refrigerant Pressure Sensor Circuit High Voltage

1. The engine is running.
2. The A/C is requested.

P0531

The A/C refrigerant pressure sensor signal voltage is less than 0.2 volt or more than 4.88 volts for more than 3 seconds.

P0532

The A/C refrigerant pressure sensor signal voltage is less than 0.2 volt for more than 3 seconds.

P0533

The A/C refrigerant pressure sensor signal voltage is more than 4.88 volts for more than 3 seconds.

1. The ECM stores the DTC information into memory when the diagnostic runs and fails.
2. The malfunction indicator lamp (MIL) will not illuminate.
3. The ECM disables the A/C compressor clutch.
4. The ECM records the operating conditions at the time the diagnostic fails. The ECM stores this information in the Failure Records.
5. The ECM will report a value of 0 kPa to the HVAC control module.
6. The driver information center will display SERVICE A/C SYSTEM.
7. The A/C OFF segment will illuminate on the HVAC control module.

1. A history DTC will clear after 40 consecutive warm-up cycles, if no failures are reported by this or any other non-emission related diagnostic.
2. The current DTC will clear when the diagnostic runs and does not fail.
3. Use a scan tool in order to clear the diagnostic trouble code.

If DTC P0532 or P0533 cannot be duplicated, reviewing the Failure Records vehicle mileage since the diagnostic test last failed may help determine how often the condition that caused the DTC to set occurs. This may assist in diagnosing the condition.

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

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

1. 3: Tests for the proper operation of the circuit in the low voltage range.
2. 4: Tests for the proper operation of the circuit in the high voltage range. If the fuse in the jumper opens when you perform this test, the signal circuit is shorted to ground.
3. 5: Tests for a short to voltage in the 5-volt reference circuit.

DTC P0531, P0532, or P0533

Ignition voltage is supplied directly to the A/C compressor clutch relay. The engine control module (ECM) controls the relay by grounding the A/C clutch relay control circuit via an internal solid state device called a driver. The primary function of the driver is to supply the ground for the component being controlled. The driver has a fault line which is monitored by the ECM. When the ECM is commanding a component ON, the voltage of the control circuit should be near 0 volts. When the ECM is commanding the control circuit to a component OFF, the voltage potential of the circuit should be near battery voltage. If the fault detection circuit senses a voltage other than what is expected, this DTC will set.

The ECM will monitor the control circuit for the following

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

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

This diagnostic procedure supports the following DTCs

1. DTC P0645 Air Conditioning (A/C) Clutch Relay Control Circuit
2. DTC P0646 Air Conditioning (A/C) Clutch Relay Control Circuit Low Voltage
3. DTC P0647 Air Conditioning (A/C) Clutch Relay Control Circuit High Voltage

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

P0645

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

P0646

The ECM detects a short to ground on the control circuit of the A/C compressor clutch relay.

P0647

The ECM detects a short to voltage on the control circuit of the A/C compressor clutch relay.

1. The ECM will not illuminate the malfunction indicator lamp (MIL).
2. The ECM will store conditions which were present when the DTC set as Failure Records data only. This information will not be stored as Freeze Frame data.

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

If DTC P0645, P0646, P0647 cannot be duplicated, reviewing the Failure Records vehicle millage since the diagnostic test last failed may help determine how often the condition that caused the DTC to set occurs. This may assist in diagnosing the condition.

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

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

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

DTC P0645, P0646, or P0647

Symptoms - HVAC Systems - Automatic

1. Perform the «Diagnostic System Check - Vehicle»(/cadillac/sts/i-2004-2007/remont/oem-general-information/#vehicle-dtc-information) in Vehicle DTC Information, before using the Symptom Tables in order to verify that all of the following are true: There are no DTCs set. The control modules can communicate via the serial data link.
2. Review the system operation in order to familiarize yourself with the system functions. Refer to the following information: «Air Delivery Description and Operation»(/cadillac/sts/i-2004-2007/remont/automatic-hvac-system/#hvac-system-automatic__air-delivery-description-and-operation) «Air Temperature Description and Operation»(/cadillac/sts/i-2004-2007/remont/automatic-hvac-system/#hvac-system-automatic__air-temperature-description-and-operation)

Visual/Physical Inspection

1. Inspect for aftermarket devices which could affect the operation of the HVAC System. Refer to «Checking Aftermarket Accessories»(/cadillac/sts/i-2004-2007/remont/body-electrical/#wiring-systems-electrical-power-management-introduction__checking-aftermarket-accessories) in Wiring Systems.
2. Inspect the easily accessible or visible system components for obvious damage or conditions which could cause the symptom.
3. Verify the A/C compressor clutch turns freely and is not seized.
4. Verify that the customer is using the correct key to enable personalization and is not inadvertently activating auxiliary HVAC controls.
5. The A/C compressor will not operate in cold outside air temperatures. Refer to «Air Temperature Description and Operation»(/cadillac/sts/i-2004-2007/remont/automatic-hvac-system/#hvac-system-automatic__air-temperature-description-and-operation) .
6. The following conditions may cause window fogging: Wet carpet or mats High humidity Interior water leak Blocked A/C evaporator drain tube Maximum passenger capacity Blocked body pressure relief valves
7. Inspect the air distribution system for causes of reduced air flow: Obstructed or dirty passenger compartment air filter, if equipped Blocked or damaged air inlet or outlet vents

Intermittent

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

Symptom List

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

1. «HVAC Compressor Clutch Does Not Engage»(/cadillac/sts/i-2004-2007/remont/automatic-hvac-system/#hvac-system-automatic__hvac-compressor-clutch-does-not-engage)
2. «HVAC Compressor Clutch Does Not Disengage»(/cadillac/sts/i-2004-2007/remont/automatic-hvac-system/#hvac-system-automatic__hvac-compressor-clutch-does-not-disengage)
3. «Blower Motor Always On»(/cadillac/sts/i-2004-2007/remont/automatic-hvac-system/#hvac-system-automatic__blower-motor-always-on)
4. «Blower Motor Inoperative»(/cadillac/sts/i-2004-2007/remont/automatic-hvac-system/#hvac-system-automatic__blower-motor-inoperative)
5. «Blower Motor Malfunction»(/cadillac/sts/i-2004-2007/remont/automatic-hvac-system/#hvac-system-automatic__blower-motor-malfunction)
6. «Too Hot in Vehicle»(/cadillac/sts/i-2004-2007/remont/automatic-hvac-system/#hvac-system-automatic)
7. «Too Cold in Vehicle»(/cadillac/sts/i-2004-2007/remont/automatic-hvac-system/#hvac-system-automatic__too-cold-in-vehicle)
8. «Air Delivery Improper»(/cadillac/sts/i-2004-2007/remont/automatic-hvac-system/#hvac-system-automatic)
9. «Air Recirculation Malfunction»(/cadillac/sts/i-2004-2007/remont/automatic-hvac-system/#hvac-system-automatic)
10. «Leak Testing»(/cadillac/sts/i-2004-2007/remont/automatic-hvac-system/#heating-ventilation-and-air-conditioning__leak-testing) in Heating, Ventilation and Air Conditioning
11. «Noise Diagnosis - Blower Motor»(/cadillac/sts/i-2004-2007/remont/automatic-hvac-system/#heating-ventilation-and-air-conditioning__noise-diagnosis-blower-motor) in Heating, Ventilation and Air Conditioning
12. «Noise Diagnosis - Air Conditioning (A/C) System»(/cadillac/sts/i-2004-2007/remont/automatic-hvac-system/#heating-ventilation-and-air-conditioning__noise-diagnosis-air-conditioning-ac) in Heating, Ventilation and Air Conditioning
13. «Odor Diagnosis»(/cadillac/sts/i-2004-2007/remont/automatic-hvac-system/#heating-ventilation-and-air-conditioning__odor-diagnosis) in Heating, Ventilation and Air Conditioning
14. «Steering Wheel Controls Inoperative»(/cadillac/sts/i-2004-2007/remont/entertainment-systems/#entertainment-system__steering-wheel-controls-inoperative) in Entertainment

HVAC Compressor Clutch Does Not Engage

HVAC Compressor Clutch Does Not Engage

HVAC Compressor Clutch Does Not Disengage

HVAC Compressor Clutch Does Not Disengage

Blower Motor Always On

Blower Motor Always On

Blower Motor Inoperative

Blower Motor Inoperative

Blower Motor Malfunction

Blower Motor Malfunction

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

1. 6: The ambient air temperature must be above 3°C (38°F) for this A/C compressor test.
2. 7: The specified values are from the A/C System Performance Test.

Too Hot in Vehicle

Too Cold in Vehicle

Too Cold in Vehicle

Scan Tool Not Completed

Refer to Air Quality Sensor (RPO K14) in the HVAC Systems Automatic Description and Operation to understand the functionality of this system. The air quality sensor sensitivity can be adjusted. Refer to Air Quality Calibration Offset .

Exhaust Odor Inside Vehicle

Exhaust Odor Inside Vehicle

1. The condition may be intermittent. Refer to «Testing for Intermittent Conditions and Poor Connections»(/cadillac/sts/i-2004-2007/remont/body-electrical/#wiring-systems-electrical-power-management-introduction__testing-for-intermittent-conditions-and-poor) in Wiring Systems.
2. Inspect the air delivery system for the following conditions: A dirty HVAC air filter An obstruction to the airflow Air leaks Misaligned air ducts Broken or binding linkages or doors

Air Delivery Improper

1. If the control A circuit of the recirculation actuator is shorted to ground, the following conditions will occur. The recirculation actuator will operate properly when recirculation is requested. The recirculation actuator will continually modulate between the outside air and recirculation positions when outside air is requested.
2. If the control B circuit of the recirculation actuator is shorted to ground, the following conditions will occur. The recirculation actuator will operate properly when outside air is requested. The recirculation actuator will continually modulate between the outside air and recirculation positions when recirculation is requested.
3. The condition may be intermittent. Refer to «Testing for Intermittent Conditions and Poor Connections»(/cadillac/sts/i-2004-2007/remont/body-electrical/#wiring-systems-electrical-power-management-introduction__testing-for-intermittent-conditions-and-poor) in Wiring Systems.
4. Inspect the recirculation door and the recirculation actuator for the following conditions: A misaligned recirculation actuator - Refer to «Recirculation Actuator Replacement»(/cadillac/sts/i-2004-2007/remont/automatic-hvac-system/#hvac-system-automatic) . Broken or binding linkages A broken or binding recirculation door An obstruction that prevents the recirculation door from operating within its full range of motion Missing seals to the recirculation door Misaligned seals to the recirculation door

Air Recirculation Malfunction

Afterblow Enable Procedure

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 reprogramming the HVAC control module, refer to Service Programming System (SPS) in Programming and Setup.

After the HVAC control module has been programmed for afterblow, the following conditions must be met for afterblow to operate

1. The engine has been turned off for at least 30 minutes.
2. The ambient air temperature is at least 21°C (70°F).
3. The A/C compressor operated for more than 2 minutes.
4. The system voltage is at least 12 volts.

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

1. The blower motor will run for 20 seconds.
2. The blower motor will be off for 10 minutes.
3. The blower motor will run for and additional 20 seconds.

Removal Procedure

1. Remove the ashtray. Refer to «Ashtray Replacement»(/cadillac/sts/i-2004-2007/remont/gauges-instrument-panels/#instrument-panel-system-displays-gauges-and-console) .
2. Remove the radio. Refer to «Radio Replacement»(/cadillac/sts/i-2004-2007/remont/entertainment-systems/#entertainment-system) .
3. Remove the HVAC control module retaining screws.
4. Disconnect the HVAC control module electrical connectors.
5. Remove the HVAC control module.

Installation Procedure

1. Install the HVAC control module.
2. Connect the HVAC control module electrical connectors.
3. Install the HVAC control module retaining screws. Tighten: Tighten the screws to 2 N.m (18 lb in).
4. Install the radio. Refer to «Radio Replacement»(/cadillac/sts/i-2004-2007/remont/entertainment-systems/#entertainment-system) .
5. Install the ashtray. Refer to «Ashtray Replacement»(/cadillac/sts/i-2004-2007/remont/gauges-instrument-panels/#instrument-panel-system-displays-gauges-and-console) .

1. Remove the right sound insulator. Refer to «Closeout/Insulator Panel Replacement - Right»(/cadillac/sts/i-2004-2007/remont/gauges-instrument-panels/#instrument-panel-system-displays-gauges-and-console) in Instrument Panel, Gages, and Console.
2. Disconnect the electrical connector from the blower motor control processor.
3. Remove the blower motor control processor retaining screw.
4. Remove the blower motor control processor from the vehicle.

1. Install the blower motor control processor.
2. Install the blower motor control processor retaining screw. Tighten: Tighten the screw to 1 N.m (9 lb in).
3. Connect the electrical connector to the blower motor control processor.
4. Install the right sound insulator. Refer to «Closeout/Insulator Panel Replacement - Right»(/cadillac/sts/i-2004-2007/remont/gauges-instrument-panels/#instrument-panel-system-displays-gauges-and-console) in Instrument Panel, Gages, and Console.

Scheme 12

HVAC Control Assembly Replacement - Auxiliary

1. Remove the air inlet assembly. Refer to «Air Inlet Assembly Replacement»(/cadillac/sts/i-2004-2007/remont/automatic-hvac-system/#heating-ventilation-and-air-conditioning) in Heating, Ventilation and Air Conditioning.
2. Disconnect the electrical connector from the recirculation actuator.
3. Remove the recirculation actuator screws (1).
4. Remove the recirculation actuator.

1. Install the recirculation actuator.
2. Install the recirculation actuator screws (1). Tighten: Tighten the screws to 1 N.m (9 lb in).
3. Connect the electrical connector to the recirculation actuator.
4. Install the air inlet assembly. Refer to «Air Inlet Assembly Replacement»(/cadillac/sts/i-2004-2007/remont/automatic-hvac-system/#heating-ventilation-and-air-conditioning) in Heating, Ventilation and Air Conditioning.

1. Remove the instrument panel (I/P) carrier. Refer to «Instrument Panel (I/P) Carrier Replacement»(/cadillac/sts/i-2004-2007/remont/gauges-instrument-panels/#instrument-panel-system-displays-gauges-and-console) in Instrument Panel, Gages and Console.
2. Disconnect the mode actuator electrical connector.
3. Remove the mode actuator screws (3).
4. Remove the mode actuator.

1. Install the mode actuator.
2. Install the mode actuator screws (2). Tighten: Tighten the screws to 1 N.m (9 lb in).
3. Connect the electrical connector to the actuator.
4. Install the I/P carrier. Refer to «Instrument Panel (I/P) Carrier Replacement»(/cadillac/sts/i-2004-2007/remont/gauges-instrument-panels/#instrument-panel-system-displays-gauges-and-console) in Instrument Panel, Gages and Console.

1. Remove the air inlet assembly. Refer to «Air Inlet Assembly Replacement»(/cadillac/sts/i-2004-2007/remont/automatic-hvac-system/#heating-ventilation-and-air-conditioning) in Heating, Ventilation and Air Conditioning.
2. Remove the right air temperature actuator screws (1).
3. Remove the right air temperature actuator.
4. Disconnect the right air temperature actuator electrical connector.

1. Connect the right air temperature actuator electrical connector.
2. Install the right air temperature actuator.
3. Install the right air temperature actuator screws (1). Tighten: Tighten the screws to 1 N.m (9 lb in).
4. Install the air inlet assembly. Refer to «Air Inlet Assembly Replacement»(/cadillac/sts/i-2004-2007/remont/automatic-hvac-system/#heating-ventilation-and-air-conditioning) in Heating, Ventilation and Air Conditioning.

1. Remove the left closeout panel. Refer to «Closeout/Insulator Panel Replacement - Left»(/cadillac/sts/i-2004-2007/remont/gauges-instrument-panels/#instrument-panel-system-displays-gauges-and-console) in Instrument Panel, Gages, and Console.
2. Disconnect the left air temperature actuator electrical connector from the actuator.
3. Remove the left air temperature actuator screws.
4. Remove the left air temperature actuator.

1. Install the left air temperature actuator.
2. Install the left air temperature actuator screws. Tighten: Tighten the screws to 1 N.m (9 lb in).
3. Connect the left air temperature actuator electrical connector to the actuator.
4. Install the left closeout panel. Refer to «Closeout/Insulator Panel Replacement - Left»(/cadillac/sts/i-2004-2007/remont/gauges-instrument-panels/#instrument-panel-system-displays-gauges-and-console) in Instrument Panel, Gages and Console

Scheme 13

Air Temperature Actuator Replacement - Auxiliary

Scheme 14

Mode Actuator Replacement - Console

1. Remove the I/P cluster trim panel. Refer to «Trim Panel Replacement - Instrument Panel (I/P) Cluster»(/cadillac/sts/i-2004-2007/remont/gauges-instrument-panels/#instrument-panel-system-displays-gauges-and-console) .
2. Remove the knee bolster reinforcement. Refer to «Knee Bolster Reinforcement Replacement»(/cadillac/sts/i-2004-2007/remont/gauges-instrument-panels/#instrument-panel-system-displays-gauges-and-console) .
3. Disconnect the aspirator hose from the HVAC module.
4. Disconnect the aspirator hose (3) from the inside air temperature sensor.
5. Remove the aspirator hose.

1. Install the aspirator hose.
2. Connect the aspirator hose (3) to the inside air temperature sensor.
3. Connect the aspirator hose to the HVAC module.
4. Install the knee bolster reinforcement. Refer to «Knee Bolster Reinforcement Replacement»(/cadillac/sts/i-2004-2007/remont/gauges-instrument-panels/#instrument-panel-system-displays-gauges-and-console) .
5. Install the I/P cluster trim panel. Refer to «Trim Panel Replacement - Instrument Panel (I/P) Cluster»(/cadillac/sts/i-2004-2007/remont/gauges-instrument-panels/#instrument-panel-system-displays-gauges-and-console) .

Scheme 15

Air Quality Sensor Replacement

1. Disconnect the ambient air temperature sensor electrical connector (1).
2. Release the ambient air temperature sensor from the clip.
3. Remove the ambient air temperature sensor from the vehicle.

1. Place the ambient air temperature sensor in position.
2. Engage the ambient air temperature sensor into the clip.
3. Connect the ambient air temperature electrical connector (1).

1. Remove the I/P cluster trim panel. Refer to «Trim Panel Replacement - Instrument Panel (I/P) Cluster»(/cadillac/sts/i-2004-2007/remont/gauges-instrument-panels/#instrument-panel-system-displays-gauges-and-console) .
2. Disconnect the aspirator hose (3) from the inside air temperature sensor (2).
3. Disconnect the electrical connector (1) from the inside air temperature sensor (2).
4. Disconnect the retaining clips and remove the inside air temperature sensor (2).

1. Install the inside air temperature sensor (2).
2. Connect the electrical connector (1) to the inside air temperature sensor (2).
3. Connect the aspirator hose (3) to the inside air temperature sensor (2).
4. Install the I/P cluster trim panel. Refer to «Trim Panel Replacement - Instrument Panel (I/P) Cluster»(/cadillac/sts/i-2004-2007/remont/gauges-instrument-panels/#instrument-panel-system-displays-gauges-and-console) .

1. Remove the defroster grille. Refer to «Defroster Grille Replacement»(/cadillac/sts/i-2004-2007/remont/gauges-instrument-panels/#instrument-panel-system-displays-gauges-and-console) in Instrument Panel, Gages and Console.
2. Remove the sunload sensor from the defroster grill by twisting the sensor 1/4 turn counter clockwise.
3. Disconnect the sunload sensor electrical connector.
4. Remove the sunload sensor.

1. Connect the sunload sensor electrical connector.
2. Install the sunload sensor to the defroster grille by twisting the sensor 1/4 turn clockwise.
3. Install the defroster grille. Refer to «Defroster Grille Replacement»(/cadillac/sts/i-2004-2007/remont/gauges-instrument-panels/#instrument-panel-system-displays-gauges-and-console) in Instrument Panel, Gages and Console.

Air Delivery Description and Operation

The Air Delivery Description and Operation is divided into 5 primary areas

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

HVAC Control Module

The HVAC control module is a class 2 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). The dash integration module (DIM), which is the vehicle power mode master, provides a device on signal. The control module supports the following features

Air Delivery Description and Operation

The HVAC control module will receive information that defines the current driver of the vehicle from the driver door module (DDM) through class 2 communication. The HVAC system will memorize the following system configurations for up to 2 unique drivers

1. Driver set temperature
2. Passenger set temperature
3. Mode
4. Blower motor speed
5. A/C compressor request, auto ON or A/C OFF

This information shall be stored inside the HVAC control module memory. When a different driver identification button is selected, the HVAC control module will recall the appropriate driver settings. When the HVAC control module is first turned on, the last stored settings for the current driver will be activated except for the rear defrost and heated seat settings.

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.

Recirculation Actuator

The recirculation actuators are 5-wire bi-directional electric motors that incorporate a feedback potentiometer. Ignition 3 voltage, low reference, control, 5-volt reference and position signal circuits enable the actuators 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 potentiometer's adjustable contact changes the door position signal between 0-5 volts.

Blower Motor Relay

The blower motor relay provides a supply voltage to the blower motor and blower motor control processor. The HVAC control module commands the blower motor relay ON anytime the commanded blower speed is not OFF.

Blower Motor Control Processor

The blower motor control processor is an interface between the HVAC control module and the blower motor. The blower motor speed control, blower motor supply voltage and ground circuits enable the control processor to operate. The HVAC control module provides a pulse width modulation (PWM) signal to the control processor in order to command the blower motor speed. The control processor uses the blower motor ground as a low side control to adjust the blower motor speed.

Air Speed

The blower motor forces air to circulate within the vehicle's interior. The vehicle operator determines the blower motors speed by placing the blower motor switch in a desired speed position or by selecting automatic operation. In manual operation, once a blower speed is selected, the blower speed remains constant, until a new speed is selected. In automatic operation, the HVAC control module will determine what blower speed is necessary in order to achieve or maintain a desired temperature.

As the requested blower speed increases, the following conditions occur

1. The HVAC control module increases the amount of time that the blower motor speed control circuit is modulated to ground.
2. The voltage and duty cycle, measured between the blower motor speed control circuit and ground, decrease.

As the requested blower speed decreases, the following conditions occur

1. The HVAC control module decreases the amount of time that the blower motor speed control circuit is modulated to ground.
2. The voltage and duty cycle, measured between the blower motor speed control circuit and ground, increase.

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 reprogramming the HVAC control module. Refer to Service Programming System (SPS) in Programming and Setup.

After the HVAC control module has been programmed for afterblow, the following conditions must be met for afterblow to operate

1. The engine has been turned OFF for at least 30 minutes.
2. The ambient air temperature is at least 21°C (70°F).
3. The A/C compressor operated for more than 2 minutes before shut down.
4. The system voltage is at least 12 volts.

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

1. The blower motor will RUN for 20 seconds.
2. The blower motor will be OFF for 10 minutes.
3. The blower motor will RUN for and additional 20 seconds.

Steering Wheel Controls

The HVAC control module receives class 2 messages from the radio interface that the driver has activated a steering wheel control switch. The steering wheel control buttons control several different functions including the following HVAC functions

1. Fan speed increase
2. Fan speed decrease
3. Driver set temperature increase
4. Driver set temperature decrease

In order to configure the steering wheel controls, refer to Radio/Audio System Description and Operation in Entertainment.

Air Distribution

The HVAC control module controls the mode actuator in order to distribute airflow to a desired outlet. The mode switch provides the vehicle operator with the ability to override the automatic setting. When the mode door is moved to the defrost position, the A/C compressor clutch engages and the recirculation actuator will be moved to the outside air position. In the outside air position, the incoming air is filtered by the passenger compartment air filter.

Recirculation

The HVAC control module controls the air intake through the recirculation actuator. Recirculation is not available when the mode is in defrost. When the mode is in defog, recirculation will only be available for 10 minutes. In the outside air position, the incoming air is filtered by the passenger compartment air filter.

Automatic Operation

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

To place the HVAC system in full automatic operation, the AUTO selection must be activated.

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

1. Regulate blower motor speed
2. Position the air temperature actuator
3. Position the mode actuator
4. Position the recirculation actuator
5. Request A/C operation

When the warmest position is selected in automatic operation the blower speed will increase gradually until the vehicle reaches normal operating temperature. When normal operating temperature is reached the blower will stay on high speed and the air temperature actuators will stay in the full heat position. The mode actuator will remain in the floor position.

When the coldest position is selected in automatic operation the blower will stay on high and the air temperature actuators will stay in the full cold position. The mode actuator will remain in the panel position and the recirculation actuator will remain in the recirculation position.

In cold temperatures, the automatic HVAC system will provide heat in the most efficient manner. The vehicle operator can select an extreme temperature setting, but the system will not warm the vehicle any faster. In warm temperatures, the automatic HVAC system will also provide air conditioning in the most efficient manner. Selecting an extreme cool temperature will not cool the vehicle any faster.

Auxiliary HVAC Control Module

The auxiliary HVAC control module is a non-GM LAN device that interfaces between the operator and the auxiliary HVAC system to maintain air temperature and air distribution settings. Five volts and ground are supplied to the rear HVAC control module. The front HVAC control module monitors the position of the rear air temperature actuator and the rear mode actuator. The front HVAC module will move the actuators to the proper position when it receives a request from the rear HVAC control module on which position to place the actuator.

Auxiliary Air Distribution

The auxiliary HVAC control module provides airflow direction and temperature control for the back seat passengers. Passengers can operate the rear HVAC control module in both manual or automatic modes. Auxiliary HVAC mode positions can be set to OFF, VENT, FLOOR and VENT, or FLOOR positions. The front HVAC module provides power and ground to the auxiliary mode actuator. The front HVAC module receives power through the ignition 1 and battery positive voltage circuits from the underhood fuse block. The auxiliary mode actuator is a reverse polarity motor. Each circuit provides both power and ground to the auxiliary mode actuator. When the auxiliary mode actuator is being held in position, both of the auxiliary mode door control circuits have 0 volts applied to both sides of the actuator motor. This holds the actuator stationary. When a mode is selected, one of the auxiliary mode door control circuits will ground, driving the auxiliary mode actuator to the desired temperature. Depending on the mode that is requested, the other auxiliary air temperature door control circuit may ground. This moves the auxiliary mode actuator into the desired position.

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.

Air Temperature Description and Operation

The air temperature controls are divided into 4 primary areas

1. Automatic Operation
2. The Heating and Air Conditioning System
3. The A/C Cycle
4. Auxiliary heating and A/C system

The HVAC control module is a class 2 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). The dash integration module (DIM), which is the vehicle power mode master, provides a device on signal. The control module supports the following features

Air Temperature Description and Operation

Remote Start and Personalization

If the remote start personalization feature for climate control is selected through radio, the HVAC control module will receive information that defines the current driver of the vehicle from the Ezkey module through GMLAN communication. This information shall be stored inside the HVAC control module memory. When a different key fob is selected, the HVAC control module will recall the appropriate driver settings. When the HVAC control module is first turned ON, the last stored settings for the current driver will be activated. Upon a battery reset, the HVAC control module shall also set the driver ID to Driver#2. The HVAC system will memorize the following system configurations for up to 2 unique drivers

1. Driver set temperature
2. Passenger set temperature
3. Mode
4. Blower motor speed
5. A/C compressor request, auto ON or A/C OFF

OnStar® Blower Control ON/OFF

During OnStar® audio control ON, the HVAC control module receives signals from OnStar® to reduce blower level to a level 4. OnStar® blower control becomes active in auto or manual blower operation. During this OnStar® blower control, if in manual or auto blower, the display will show AUTO for blower display. This blower reduction is to ensure that all incoming and outgoing voice calls will be recognized by the OnStar® module. The driver is allowed to override the OnStar® auto blower level by increasing or decreasing it manually to any desired level. When OnStar® no longer sends the request for blower control the HVAC control module will cancel OnStar® blower control and resume previous blower level if no manual override of the blower was selected.

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 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 Sensors

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

1. Ambient
2. Inside

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 decreases as the resistance decreases. The sensor signal varies between 0-5 volts. The HVAC control module converts the signal to a range between 0-255 counts.

The inside temperature sensor operates within a temperature range between -6.5 to +57.5°C (+20.3 to +135.5°F). If the sensor is shorted to ground, voltage, or an open, the system will operate using an estimated default value to allow the system to operate. The ambient sensor operates within a temperature range between -30 to +51°C (-22 to +123.8°F). If the HVAC control module has determined that the ambient temperature sensor has failed, the driver information center (DIC) display shall display 59°F in place of the outside air temperature. If the sensor is shorted to ground, voltage, or an open, the system will operate using an estimated default value to allow the system to operate. If the engine coolant temperature is not more than 3°C (5.4°F) above the sensor reading, or if the engine has not been started in 3 hours, then the actual ambient air temperature sensor reading is displayed. Also at vehicle speeds greater than 35 km/h (22 mph), the ambient air temperature displayed may be allowed to increase, but only at a slow, filtered rate. The DIC displays the ambient air temperature value that it receives from the HVAC control module through a class 2 message. The ambient air temperature value can be updated by an outside air instant update feature.

To use this feature, press the following switches on the HVAC control module simultaneously

1. AUTO
2. MODE UP
3. LEFT TEMPERATURE UP

Sunload Sensor

The sunload sensor is a 2-wire photo diode. The vehicle uses left and right sunload sensors. The 2 sensors are integrated into the sunload sensor assembly along with the ambient light sensor. Low reference and signal circuits enable the sensor to operate. As the sunload increases, the sensor signal decreases. The sensor operates within an intensity range between completely dark and bright. The sensor signal varies between 0-5 volts. The HVAC control module converts the signal to a range between 0-255 counts. The sunload sensor provides the HVAC control module a measurement of the amount of light shining on the vehicle. Bright or high intensity light causes the vehicle's inside temperature to increase. The HVAC system compensates for the increased temperature by diverting additional cool air into the vehicle. If the sensor is open or shorted, no sunload adjustment occurs and the SERVICE A/C SYSTEM message is displayed.

Evaporator Temperature Sensor

The HVAC control module monitors the temperature of the air passing through the evaporator by the A/C evaporator air temperature sensor. This sensor is located on the evaporator core. The temperature is used to cycle the A/C compressor ON and OFF to prevent the evaporator core from freezing. A thermistor inside the sensor varies its resistance to monitor the evaporator air temperature. The HVAC control module monitors the voltage drop across the thermistor when supplied with a 5-volt reference signal. The HVAC control module will send a class 2 message to the engine control module (ECM) to stop requesting the A/C compressor clutch operation if the temperature drops below 3°C (37°F). The sensor must be above 4°C (39°F) to request the A/C compressor clutch again.

The sensor operates within a temperature range between -40 to +215°C (-40 to +355°F). If the HVAC control module detects an open in the evaporator temperature sensor or circuit, the class 2 message sent to the ECM will not submit the A/C ON request. The HVAC control module will then send a request to the radio for display of the SERVICE A/C SYSTEM that will be displayed on the DIC. The HVAC control module will also display A/C OFF on the module as long as the condition is present.

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 A/C refrigerant pressure sensor prevents the A/C system from operating when an excessively high or low pressure condition exists.

If the ECM detects a failure in the A/C refrigerant pressure sensor or circuit, the class 2 message sent to the HVAC control module will be invalid. The HVAC control module will then send a request to the radio for display of the SERVICE A/C SYSTEM that will be displayed on the DIC. The HVAC control module will also display A/C OFF on the module as long as the condition is present.

Air Quality Sensor (RPO K14)

Warning - The air quality sensor recognizes carbon monoxide but is not designed as a safety feature to protect you from carbon monoxide. The air quality sensor is designed to limit your exposure to gasoline exhaust fumes and or diesel exhaust fumes that could enter into the passenger compartment from nearby vehicles for a limited amount of time. The HVAC control module monitors the outside air quality while in AUTO mode via the air quality sensor assembly. You can activate the air quality sensor on your vehicle, if equipped, by pressing the Auto button on the HVAC module. The air quality sensor is a 5-wire sensor, 1 ignition voltage circuit, 2 ground circuit, and 2 control circuits. There are 2 sensors inside the air quality sensor assembly. A hydro carbon (HC) sensor that is used for detecting gasoline exhaust fumes and a Nox sensor that is used for detecting nitrous oxide, diesel exhaust fumes. The HVAC control module outputs a 5-volt signal on the HC and Nox control circuits and operates in a range between 0-5 volts. The air quality sensor operates using an algorithm that can control the recirc actuator at any time when the HVAC module is in the AUTO mode. The algorithm is updated constantly because air quality from place to place can be very different and still considered normal for that area. The HVAC module updates the air quality sensor calibration approximately 4 times per second. The air quality sensor input to the HVAC module is compared to the previously updated air quality sensor calibration. If the voltage difference is great enough the recirc actuator will be controlled to recirc, outside air, or partial recirc outside air position based on the air quality sensor input. When air quality around the front of the vehicle is poor, the air quality sensor system operates as follows: Poor air quality with high HC levels will cause the HC control circuit to read a lower voltage. Poor air quality with high Nox levels will cause the Nox control circuit to read a higher voltage. The recirculation actuator is forced to the recirculation position. The recirc symbol on the HVAC module will illuminate. The recirc icon will not illuminate if the recirc actuator is already in the auto recirc position. When air quality around the front of the vehicle is normal, the air quality sensor system operates as follows: Normal air quality levels the HC control circuit will recognize very little voltage change from the previously updated calibration. Normal air quality levels the Nox control circuit will recognize very little voltage change from the previously updated calibration. The recirculation actuator position is not controlled by the air quality sensor system. The following are conditions that will prevent the air quality sensor from controlling the recirc actuator: A/C OFF conditions (compressor OFF) prevents air quality sensor from changing the current position of the actuator). Coolant temperature below 37°C (99°F) during warm up will prevent the blower from operating and air quality sensor from controlling the recirc position. Outside air temperature less than 5°C (41°F) (prevents air quality sensor from changing the current position of the actuator). Outside air temperature less than 15°C (59°F) and A/C high side pressure less than 196 kpa (28 psi) (prevents air quality sensor from changing the current position of the actuator). 28 seconds sensor warm-up time after ignition is turned ON (prevents air quality sensor from changing the current position of the actuator). Evaporator temperature sensor failure. Customer manually selects defrost or defog (forces actuator to outside air position). Customer manually selects recirc or outside air position. Coolant temperature above 112°C (V8), 119°C (HFV6) the actuator is forced to the recirc position. When coolant temperature drops below 109°C (V8), 116°C (HFV6) forced recirc is canceled. A/C pressure above 2 500 kpa (362 psi) the actuator is forces to the recirc position. When A/C pressure drops below 2 000 kpa (290 psi) forced recirc is canceled. The following describes the recirc actuator function after the air quality sensor has canceled the command to recirc. Full recirc position will be held for 2 minutes when vehicle speed is less than 10 km/h (6.3 mph). After 2 minutes expires the recirc door will move to full outside air position. Partial recirc, outside air position will be held for 2 minutes when vehicle speed is above 20 km/h (12.5 mph). After 2 minutes expires the recirc door will move to full outside air position. Full outside air position if vehicle speed is greater than 60 km/h (37 mph) and blower is not on high speed. The instrument panel module (IPM) shall provide the GMLAN Option Information for " Climate Air Quality Sensor Present" and "Climate Control Air Quality Sensitivity Selection" to the HVAC control module. Based on the option information received by the HVAC control module by the IPM during battery connect or sensitivity calibration setting change and ignition ON, the HVAC control module will choose 1 of 7 different sensitivity calibration settings stored in the HVAC module. The IPM sends the signal that tells the HVAC control module which sensitivity settings to use. The IPM sends a GMLAN message of 0 which tells the HVAC control module to use the default level 4 sensitivity calibration. The air quality sensitivity message sent to the HVAC module can be changed through the IPM with a TECH 2 and has 7 different air quality sensor calibration settings to choose from, 1 being the most sensitive to exhaust fumes and 7 being the least sensitive to exhaust fumes. The driver information center (DIC) will display the SERVICE A/C SYSTEM message if the HVAC system has detected a short to ground in the air quality sensor circuit. An open circuit or a short to voltage in the air quality sensor circuit will be diagnosed through symptom based diagnostics because both of these conditions will not turn on the SERVICE A/C SYSTEM message or set a trouble code.

Heating and A/C Operation

The purpose of the heating and A/C system is to provide the following

1. Heated air
2. Cooled air
3. Remove humidity from the interior of the vehicle
4. Reduce windshield fogging

Regardless of the temperature setting, the following can effect the rate that the HVAC system can achieve a desired temperature

1. Recirculation actuator setting
2. Difference between inside and desired temperature
3. Difference between ambient and desired temperature
4. Blower motor speed setting
5. Mode setting

The HVAC control module commands or monitors the following actions when an air temperature setting is selected.

1. WARMEST POSITION-The air temperature actuator door position directs maximum air flow through the heater core.
2. COLDEST POSITION-The air temperature actuator door position directs maximum air flow around the heater core.
3. BETWEEN THE WARMEST AND COLDEST POSITION-The following sensors are monitored to direct the appropriate amount of air through the heater core to achieve the desired temperature: Sunload Ambient temperature Inside temperature

The A/C system is engaged by selecting any switch on the HVAC control module except the A/C OFF switch. The A/C switch will illuminate A/C OFF when the A/C switch is selected. The control module sends a class 2 A/C request message to the engine control module (ECM) for A/C compressor clutch operation. The following conditions must be met in order for the ECM to turn on the compressor clutch

1. HVAC control module Evaporator Temperature more than 4°C (39°F) Control module operating range 9-16 volts
2. ECM Engine coolant temperature (ECT) is less than 125°C (257°F) or 120°C (248°F) for PV8 Engine RPM is between 0-6,000 RPM. A/C pressure is between 3 137 kPa (455 psi) or 2 850 kPa (413 psi) for PV8 and 193 kPa (28 psi) or 200 kPa (29 psi) for PV8.

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

1. Throttle position is 100 percent.
2. A/C pressure is more than 3 137 kPa (455 psi) or 2 850 kPa (413 psi) for PV8.
3. A/C pressure is less than 193 kPa (28 psi) or 200 kPa (29 psi) for PV8.
4. Engine coolant temperature (ECT) is more than 125°C (257°F) or 120°C (248°F) for PV8.
5. Engine speed is more than 5,500 RPM.
6. Transmission shift
7. ECM detects excessive torque load.
8. ECM detects insufficient idle quality.
9. ECM detects a hard launch condition.

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

Dual Zone Operation

The HVAC control module has temperature settings for the driver and the passenger. If the passenger setting is turned OFF then the driver setting controls both driver and passenger temperature actuators. The passenger setting cannot be used without the driver setting also being ON. The passenger setting can be turned ON or OFF by pressing the power button in the center of the passenger temperature rocker switch. When the passenger setting is ON, the passenger temperature can be adjusted independently from the driver setting and the passenger temperature is displayed on the passenger side of the control module. A different sunload on one side of the vehicle may cause different discharge air temperatures, even when the passenger setting is not turned ON.

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

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

1. The blower motor switch must be in the AUTO position.
2. The air temperature switch must be in any other position other than 60 or 90 degrees.
3. The mode switch must be in the AUTO position.

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

1. Regulate blower motor speed
2. Position the air temperature actuator
3. Position the mode actuator
4. Position the recirculation actuator
5. Request A/C operation

When the warmest position is selected in automatic operation, the blower speed will increase gradually, until the vehicle reaches normal operating temperature. When normal operating temperature is reached, the blower will stay on high speed and the air temperature actuators will stay in the full heat position. When the coldest position is selected in automatic operation, the blower will stay on high and the air temperature actuators will stay in the full cold position.

In cold temperatures, the automatic HVAC system will provide heat in the most efficient manner. The vehicle operator can select an extreme temperature setting, but the system will not warm the vehicle any faster. In warm temperatures, the automatic HVAC system will also provide air conditioning in the most efficient manner. Selecting an extremely cool temperature will not cool the vehicle any faster.

The auxiliary HVAC control module is a non-GM LAN device that interfaces between the operator and the auxiliary HVAC system to maintain air temperature and air distribution settings. Five volts and ground are supplied to the rear HVAC control module. The front HVAC control module monitors the position of the rear air temperature actuator and the rear mode actuator. The front HVAC module will move the actuators to the proper position when it receives a request from the rear HVAC control module on which position to place the actuator.

Auxiliary Heating and A/C Operation

The auxiliary HVAC control module provides airflow direction and temperature control for the back seat passengers. Passengers can operate the rear HVAC control module in both manual or automatic modes. Auxiliary HVAC temperatures can be set cooler or warmer than the front primary HVAC setting. The front HVAC module provides power and ground to the auxiliary air temperature actuator. The front HVAC module receives power through the ignition 1 and battery positive voltage circuits from the underhood fuse block. The auxiliary air temperature actuator is a reverse polarity motor. Each circuit provides both power and ground to the auxiliary air temperature actuator. When the auxiliary air temperature actuator is being held in position, both of the auxiliary air temperature door control circuits have 0 volts applied to both sides of the actuator motor. This holds the actuator stationary. When a cooler temperature is requested, one of the auxiliary air temperature door control circuits will ground, driving the auxiliary air temperature actuator to the desired temperature. When a warmer temperature is requested, the other auxiliary air temperature door control circuit will ground. This moves the auxiliary air temperature actuator into the desired position.

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 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 HVAC control module receives class 2 messages from the radio interface that the driver has activated a steering wheel control switch. The steering wheel control buttons can be reconfigured to control the following functions

1. Fan speed increase
2. Fan speed decrease
3. Driver set temperature increase
4. Driver set temperature decrease

In order to configure the steering wheel controls, refer to Radio/Audio System Description and Operation in Entertainment. The HVAC system interprets the fan and set temperature switches on the steering wheel as if the driver had activated the same switch function on the HVAC control module.

A/C Cycle

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

The Denso 7SBU16 variable displacement swash plate A/C compressor is belt driven and operates when the magnetic clutch is engaged. The compressor builds pressure on the vapor refrigerant. Compressing the refrigerant also adds heat to the refrigerant. The refrigerant is discharged from the compressor, through the discharge hose, and forced to flow to the condenser and then through the balance of the A/C system. The A/C system is mechanically protected with the use of a high pressure relief valve. If the high pressure switch were to fail or if the refrigerant system becomes restricted and refrigerant pressure continues to rise, the high pressure relief will pop open and release refrigerant from the system.

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

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

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

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

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

Special Tools

Special Tools Illustration Tool Number/ Description J 39200 Tech 2

Scheme 16

See also:
• DTC Symptom Description
• Diagnostic System Check - Vehicle
• Testing for Intermittent Conditions and Poor Connections
• Circuit Testing
• Wiring Repairs
• Connector Repairs
• Control Module References
• Air Conditioning (A/C) Refrigerant Pressure Sensor Replacement
• Checking Aftermarket Accessories
• Leak Testing
• Noise Diagnosis - Blower Motor
• Noise Diagnosis - Air Conditioning (A/C) System
• Odor Diagnosis
• Steering Wheel Controls Inoperative
• After Boil Coolant Pump Inoperative
• Heating Performance Diagnostic
• Service Programming System (SPS)
• Ashtray Replacement
• Radio Replacement
• Fastener Notice
• Fastener Tightening Specifications
• Radio/Audio System Description and Operation
• HVAC Schematics
• HVAC Connector End Views
• Air Delivery Description and Operation
• Air Temperature Description and Operation
• HVAC Compressor Clutch Does Not Engage
• HVAC Compressor Clutch Does Not Disengage
• Blower Motor Always On
• Blower Motor Inoperative
• Blower Motor Malfunction
• Too Cold in Vehicle
• Fastener Tightening Specifications