HVAC System - Automatic Cadillac DTS I

Fastener Tightening Specifications

Sensor Resistance Table

Scheme 49

Scheme 50

Scheme 51

Scheme 52

Scheme 53

DIAGNOSTIC CODE INDEX

DIAGNOSTIC CODE INDEX

Diagnostic Instructions

1. Perform the «Diagnostic System Check - Vehicle»(/cadillac/dts/i-2005-2011/remont/oem-general-information/#vehicle-diagnostic-information__diagnostic-system-check-vehicle) prior to using this diagnostic procedure.
2. Review «Strategy Based Diagnosis»(/cadillac/dts/i-2005-2011/remont/oem-general-information/#vehicle-diagnostic-information__strategy-based-diagnosis) for an overview of the diagnostic approach.
3. «Diagnostic Procedure Instructions»(/cadillac/dts/i-2005-2011/remont/oem-general-information/#vehicle-diagnostic-information__diagnostic-procedure-instructions) provides an overview of each diagnostic category.

Diagnostic Fault Information

Circuit/System Description

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

Conditions for Running the DTC

Ignition ON.

Conditions for Setting the DTC

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

Action Taken When the DTC Sets

1. The HVAC control module will display dashes for outside air temperature.
2. The DIC will display SERVICE A/C SYSTEM.
3. The system operates using a default value.

Conditions for Clearing the DTC

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

Diagnostic Aids

If the ambient air temperature sensor has an out of range condition caused by a short to voltage, short to ground, or open/high resistance the scan tool will display the last normal operating range.

Reference Information

Schematic Reference

HVAC Schematics

Connector End View Reference

Component Connector End Views

Description and Operation

1. «Air Delivery Description and Operation»(/cadillac/dts/i-2005-2011/remont/automatic-hvac-system/#hvac-system-automatic__air-delivery-description-operation)
2. «Air Temperature Description and Operation»(/cadillac/dts/i-2005-2011/remont/automatic-hvac-system/#hvac-system-automatic__air-temperature-description-operation)

Electrical Information Reference

1. «Circuit Testing»(/cadillac/dts/i-2005-2011/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-service-troubleshooting-diagnosis__circuit-testing)
2. «Connector Repairs»(/cadillac/dts/i-2005-2011/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-service-troubleshooting-diagnosis__connector-repairs)
3. «Testing for Intermittent Conditions and Poor Connections»(/cadillac/dts/i-2005-2011/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-service-troubleshooting-diagnosis__testing-for-intermittent-conditions-poor)
4. «Wiring Repairs»(/cadillac/dts/i-2005-2011/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-service-troubleshooting-diagnosis__wiring-repairs)

Scan Tool Reference

Control Module References for scan tool information

Circuit/System Testing

1. Ignition OFF, disconnect the harness connector at the ambient air temperature sensor.
2. Ignition OFF, test for less than 1 ohm between the low reference circuit terminal B and ground. If greater than the specified range, test the low reference circuit for an open/high resistance. If the circuit tests normal, replace the HVAC control module.
3. Ignition ON, test for 5 volts between the signal circuit terminal A and the low reference circuit terminal B. If greater than the specified range, test the signal circuit for a short to voltage. If the circuit tests normal, replace the HVAC control module. If less than the specified range, test the signal circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the HVAC control module.
4. If all circuits test normal, test or replace the ambient air temperature sensor.

Repair Procedures

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

1. «Ambient Air Temperature Sensor Replacement»(/cadillac/dts/i-2005-2011/remont/automatic-hvac-system/#hvac-system-automatic)
2. «Control Module References»(/cadillac/dts/i-2005-2011/remont/communication-devices/#programming-and-setup-all-systems__control-module-references) for HVAC control module replacement, setup, and programming

1. Perform the «Diagnostic System Check - Vehicle»(/cadillac/dts/i-2005-2011/remont/oem-general-information/#vehicle-diagnostic-information__diagnostic-system-check-vehicle) prior to using this diagnostic procedure.
2. Review «Strategy Based Diagnosis»(/cadillac/dts/i-2005-2011/remont/oem-general-information/#vehicle-diagnostic-information__strategy-based-diagnosis) for an overview of the diagnostic approach.
3. «Diagnostic Procedure Instructions»(/cadillac/dts/i-2005-2011/remont/oem-general-information/#vehicle-diagnostic-information__diagnostic-procedure-instructions) provides an overview of each diagnostic category.

The HVAC control module supplies the evaporator temperature and inside air temperature sensors with a low reference circuit and 5-volt signal circuit. The HVAC control module determines the voltage drop across the sensors, which is proportional to temperature. As the air temperature increases, the sensor resistance decreases. As the air temperature decreases, the sensor resistance increases. The inside air temperature sensor assembly has an internal fan that draws air across the sensor and is controlled by the HVAC control module. The internal fan motor is connected to body ground.

Ignition ON.

B0163

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

B3933

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

B0163

1. The system operates using a default value.
2. The HVAC control module will display dashes for outside air temperature.
3. The DIC will display SERVICE A/C SYSTEM.

B3933

1. The A/C compressor is disabled.
2. The DIC will display SERVICE A/C SYSTEM.

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

Schematic Reference

HVAC Schematics

Connector End View Reference

Component Connector End Views

Description and Operation

Air Temperature Description and Operation

Electrical Information Reference

1. «Circuit Testing»(/cadillac/dts/i-2005-2011/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-service-troubleshooting-diagnosis__circuit-testing)
2. «Connector Repairs»(/cadillac/dts/i-2005-2011/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-service-troubleshooting-diagnosis__connector-repairs)
3. «Testing for Intermittent Conditions and Poor Connections»(/cadillac/dts/i-2005-2011/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-service-troubleshooting-diagnosis__testing-for-intermittent-conditions-poor)
4. «Wiring Repairs»(/cadillac/dts/i-2005-2011/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-service-troubleshooting-diagnosis__wiring-repairs)

Scan Tool Reference

Control Module References for scan tool information

1. Ignition OFF, disconnect the harness connector at the appropriate temperature sensor.
2. Ignition OFF, test for less than 1 ohm between the low reference circuit terminal listed below and ground. Passenger compartment temperature sensor circuit terminal D Evaporator temperature sensor circuit terminal B If greater than the specified range, test the low reference circuit for an open/high resistance. If the circuit tests normal, replace the HVAC control module.
3. Ignition ON, verify the appropriate scan tool Temperature Sensor parameter is greater than 215°C (419°F). If less than the specified range, test the signal circuit for a short to ground. If the circuit tests normal, replace the HVAC control module.
4. Install a 3A fused jumper wire between the signal circuit terminal A and the low reference circuit terminal listed below. Verify the appropriate scan tool Temperature Sensor parameter is less than -36°C (-38°F). Passenger compartment temperature sensor circuit terminal D Evaporator temperature sensor circuit terminal B If greater than the specified range, test the signal circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the HVAC control module.
5. If all circuits test normal, test or replace the temperature sensor.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

1. «Heater and Air Conditioning Control Wiring Harness Replacement (w/Evaporator Temperature Sensor)»(/cadillac/dts/i-2005-2011/remont/automatic-hvac-system/#hvac-system-automatic)
2. «Inside Air Temperature Sensor Replacement»(/cadillac/dts/i-2005-2011/remont/automatic-hvac-system/#hvac-system-automatic)
3. «Control Module References»(/cadillac/dts/i-2005-2011/remont/communication-devices/#programming-and-setup-all-systems__control-module-references) for HVAC control module replacement, setup, and programming

1. Perform the «Diagnostic System Check - Vehicle»(/cadillac/dts/i-2005-2011/remont/oem-general-information/#vehicle-diagnostic-information__diagnostic-system-check-vehicle) prior to using this diagnostic procedure.
2. Review «Strategy Based Diagnosis»(/cadillac/dts/i-2005-2011/remont/oem-general-information/#vehicle-diagnostic-information__strategy-based-diagnosis) for an overview of the diagnostic approach.
3. «Diagnostic Procedure Instructions»(/cadillac/dts/i-2005-2011/remont/oem-general-information/#vehicle-diagnostic-information__diagnostic-procedure-instructions) provides an overview of each diagnostic category.

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 very 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 with a measurement of the amount of light shining on the vehicle. Bright or high intensity light causes the vehicles interior temperature to increase. The HVAC system compensates for the increased temperature by diverting additional cool air into the vehicle.

Ignition ON.

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. The HVAC control module will display dashes for outside air temperature.
2. The driver information center (DIC) will display SERVICE A/C SYSTEM.
3. If the DTC is set the system will act as if no sunload condition exists.

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

Schematic Reference

HVAC Schematics

Connector End View Reference

Component Connector End Views

Description and Operation

Air Temperature Description and Operation

Electrical Information Reference

1. «Circuit Testing»(/cadillac/dts/i-2005-2011/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-service-troubleshooting-diagnosis__circuit-testing)
2. «Connector Repairs»(/cadillac/dts/i-2005-2011/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-service-troubleshooting-diagnosis__connector-repairs)
3. «Testing for Intermittent Conditions and Poor Connections»(/cadillac/dts/i-2005-2011/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-service-troubleshooting-diagnosis__testing-for-intermittent-conditions-poor)
4. «Wiring Repairs»(/cadillac/dts/i-2005-2011/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-service-troubleshooting-diagnosis__wiring-repairs)

Scan Tool Reference

Control Module References for scan tool information

1. Ignition OFF, disconnect the harness connector at the sunload sensor.
2. Test for less than 1.0 ohm between the ground circuit terminal C and ground. If greater than the specified range, test the ground circuit for an open/high resistance.
3. Ignition ON, verify the appropriate scan tool Sunload Sensor parameter is greater than 250 counts. If not the specified value, test the appropriate signal circuit terminal listed below for a short to ground. If the circuit tests normal, replace the HVAC control module. Left sunload sensor circuit terminal A Right sunload sensor circuit terminal B
4. Install a 3A fused jumper wire between the ground circuit terminal C and the signal circuit terminal of the appropriate sensor listed below. Verify the appropriate scan tool Sunload Sensor parameter is less than 5 counts. Left sunload sensor circuit terminal A Right sunload sensor circuit terminal B If not the specified value, test the signal circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the HVAC control module.
5. If all circuits test normal, test or replace the sunload sensor.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

1. «Sun Load Sensor Replacement»(/cadillac/dts/i-2005-2011/remont/automatic-hvac-system/#hvac-system-automatic)
2. «Control Module References»(/cadillac/dts/i-2005-2011/remont/communication-devices/#programming-and-setup-all-systems__control-module-references) for HVAC control module replacement, setup, and programming

1. Perform the «Diagnostic System Check - Vehicle»(/cadillac/dts/i-2005-2011/remont/oem-general-information/#vehicle-diagnostic-information__diagnostic-system-check-vehicle) prior to using this diagnostic procedure.
2. Review «Strategy Based Diagnosis»(/cadillac/dts/i-2005-2011/remont/oem-general-information/#vehicle-diagnostic-information__strategy-based-diagnosis) for an overview of the diagnostic approach.
3. «Diagnostic Procedure Instructions»(/cadillac/dts/i-2005-2011/remont/oem-general-information/#vehicle-diagnostic-information__diagnostic-procedure-instructions) provides an overview of each diagnostic category.

The HVAC control module controls the HVAC door actuators to regulate the airflow through the HVAC system. Each actuator consists of an electric motor and a potentiometer. The module supplies a low reference and 5-volt reference source voltage to the potentiometer. The HVAC control module monitors the voltage drop across the potentiometer on the door position signal circuit. When the actuator shaft rotates, the voltage on the door position signal circuit changes. The HVAC control module supplies the actuator motor with a 12-volt control circuit and a ground control circuit. The HVAC module controls the direction of the actuator door by changing the polarity of the control circuits.

1. Ignition ON.
2. Ignition voltage is between 9-16 volts.
3. The HVAC module is ON.

The actual door position differs from the commanded door position by greater than 4 counts or the HVAC control module detects the door position signal circuit is less than 7 counts or greater than 250 counts.

Driver A and driver B circuits are deactivated for the appropriate actuator.

1. The DTC becomes history when the HVAC control module no longer detects the condition that set the DTC.
2. The history DTC will clear after 100 fault free ignition cycles.
3. The DTC can be cleared with a scan tool.

Schematic Reference

HVAC Schematics

Connector End View Reference

Component Connector End Views

Description and Operation

Air Temperature Description and Operation

Electrical Information Reference

1. «Circuit Testing»(/cadillac/dts/i-2005-2011/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-service-troubleshooting-diagnosis__circuit-testing)
2. «Connector Repairs»(/cadillac/dts/i-2005-2011/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-service-troubleshooting-diagnosis__connector-repairs)
3. «Testing for Intermittent Conditions and Poor Connections»(/cadillac/dts/i-2005-2011/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-service-troubleshooting-diagnosis__testing-for-intermittent-conditions-poor)
4. «Wiring Repairs»(/cadillac/dts/i-2005-2011/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-service-troubleshooting-diagnosis__wiring-repairs)

Scan Tool Reference

Control Module References for scan tool information

1. Ignition OFF, disconnect the harness connector at the appropriate actuator.
2. Ignition OFF, test for less than 1.0 ohm between the low reference circuit terminal 2 and ground. If greater than the specified range, test the low reference circuit for an open/high resistance. If the circuit tests normal, replace the HVAC control module.
3. Ignition ON, test for 4.8-5.2 volts between the 5-volt reference circuit terminal 1 and ground. If less than the specified range, test the 5-volt reference circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the HVAC control module. If greater than the specified range, test the 5-volt reference circuit for a short to voltage. If the circuit tests normal, replace the HVAC control module.
4. Verify the appropriate scan tool parameter is less than 3 counts. If greater than the specified range, test the signal circuit for a short to ground. If the circuit tests normal, replace the HVAC control module.
5. Install a 3A fused jumper wire between the signal circuit terminal 3 and the low reference circuit terminal 2. Verify the appropriate scan tool actuator parameter is greater than 250 counts. If less than the specified range, test the signal circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the HVAC control module.
6. Reconnect the harness connector at the appropriate actuator.
7. Disconnect the HVAC control module.
8. Install a 20- amp fused jumper wire between the appropriate control circuit terminal and 12 volts. Momentarily install a jumper wire between the appropriate control circuit terminal and ground. The actuator should move. If the actuator does not move in both directions, test the control circuits for a short to voltage, short to ground or an open/high resistance. If the circuits test normal, test or replace the inoperative actuator.
9. If all circuits test normal, replace the HVAC control module.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

1. «Recirculation Actuator Replacement»(/cadillac/dts/i-2005-2011/remont/automatic-hvac-system/#hvac-system-automatic)
2. «Mode Actuator Replacement»(/cadillac/dts/i-2005-2011/remont/automatic-hvac-system/#hvac-system-automatic)
3. «Air Temperature Actuator Replacement - Left Side»(/cadillac/dts/i-2005-2011/remont/automatic-hvac-system/#hvac-system-automatic)
4. «Air Temperature Actuator Replacement - Right Side»(/cadillac/dts/i-2005-2011/remont/automatic-hvac-system/#hvac-system-automatic)
5. «Auxiliary Temperature Valve Actuator Replacement»(/cadillac/dts/i-2005-2011/remont/automatic-hvac-system/#hvac-system-automatic)
6. «Auxiliary Mode Valve Actuator Replacement»(/cadillac/dts/i-2005-2011/remont/automatic-hvac-system/#hvac-system-automatic)

1. Perform the «Diagnostic System Check - Vehicle»(/cadillac/dts/i-2005-2011/remont/oem-general-information/#vehicle-diagnostic-information__diagnostic-system-check-vehicle) prior to using this diagnostic procedure.
2. Review «Strategy Based Diagnosis»(/cadillac/dts/i-2005-2011/remont/oem-general-information/#vehicle-diagnostic-information__strategy-based-diagnosis) for an overview of the diagnostic approach.
3. «Diagnostic Procedure Instructions»(/cadillac/dts/i-2005-2011/remont/oem-general-information/#vehicle-diagnostic-information__diagnostic-procedure-instructions) provides an overview of each diagnostic category.

The engine control module (ECM) monitors the high side refrigerant pressure through the A/C refrigerant pressure sensor. The ECM supplies a 5-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 low, the signal voltage is low. When the pressure is high, the ECM commands the cooling fans on. When pressure is too high or too low, the ECM will not allow the A/C compressor clutch to engage.

The engine is running.

1. The ECM detects that the A/C pressure is less than 1 psi (0.01 volt).
2. The ECM detects that the A/C pressure is greater than 425 psi (4.90 volts).

1. The ECM will not illuminate the malfunction indicator lamp (MIL).
2. The ECM stores the failure records.
3. The A/C compressor clutch is disabled.

1. The history DTC will clear after 40 consecutive ignition cycles have occurred without a malfunction.
2. The DTC will become history if the ECM no longer detects a failure.

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

Schematic Reference

HVAC Schematics

Connector End View Reference

Component Connector End Views

Description and Operation

Air Temperature Description and Operation

Electrical Information Reference

1. «Circuit Testing»(/cadillac/dts/i-2005-2011/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-service-troubleshooting-diagnosis__circuit-testing)
2. «Connector Repairs»(/cadillac/dts/i-2005-2011/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-service-troubleshooting-diagnosis__connector-repairs)
3. «Testing for Intermittent Conditions and Poor Connections»(/cadillac/dts/i-2005-2011/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-service-troubleshooting-diagnosis__testing-for-intermittent-conditions-poor)
4. «Wiring Repairs»(/cadillac/dts/i-2005-2011/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-service-troubleshooting-diagnosis__wiring-repairs)

Scan Tool Reference

Control Module References for scan tool information

Circuit/System Verification

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

1. Ignition OFF, disconnect the harness connector at the A/C refrigerant pressure sensor.
2. Ignition OFF, test for less than 10 ohms between the low reference circuit terminal 1 and ground. If greater than the specified range, test the low reference circuit for an open/high resistance. If the circuit tests normal, replace the ECM.
3. Ignition ON, test for 4.8-5.2 volts between the 5-volt reference circuit terminal 2 and ground. If less than the specified range, test the 5-volt reference circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the ECM. If greater than the specified range, test the 5-volt reference circuit for a short to voltage. If the circuit tests normal, replace the ECM.
4. Verify the scan tool A/C High Side Pressure Sensor parameter is less than 0.1 volts (1 psi). If greater than the specified range, test the signal circuit terminal 3 for a short to voltage. If the circuit tests normal, replace the ECM.
5. Install a 3A fused jumper wire between the signal circuit terminal 3 and the 5-volt reference circuit terminal 2. Verify the scan tool A/C High Side Pressure Sensor parameter is greater than 4.90 volts (425 psi). If less than the specified range, test the signal circuit for short to ground or an open/high resistance. If the circuit tests normal, replace the ECM.
6. If all circuits test normal, test or replace the A/C refrigerant pressure sensor.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

1. «Air Conditioning (A/C) Refrigerant Pressure Sensor Replacement»(/cadillac/dts/i-2005-2011/remont/automatic-hvac-system/#heating-ventilation-and-air-conditioning)
2. «Control Module References»(/cadillac/dts/i-2005-2011/remont/communication-devices/#programming-and-setup-all-systems__control-module-references) for the ECM replacement, setup, and programming

1. Perform the «Diagnostic System Check - Vehicle»(/cadillac/dts/i-2005-2011/remont/oem-general-information/#vehicle-diagnostic-information__diagnostic-system-check-vehicle) prior to using this diagnostic procedure.
2. Review «Strategy Based Diagnosis»(/cadillac/dts/i-2005-2011/remont/oem-general-information/#vehicle-diagnostic-information__strategy-based-diagnosis) for an overview of the diagnostic approach.
3. «Diagnostic Procedure Instructions»(/cadillac/dts/i-2005-2011/remont/oem-general-information/#vehicle-diagnostic-information__diagnostic-procedure-instructions) provides an overview of each diagnostic category.

When the A/C switch is pressed, the HVAC control assembly sends a serial data message to the engine control module (ECM) for an A/C request. This input will request the ECM to ground the A/C compressor clutch relay control circuit, which will switch the A/C CLTCH relay. With the relay contacts closed, battery voltage is supplied to the A/C compressor clutch assembly.

1. The ignition voltage is between 11-18 volts.
2. The engine speed is greater than 600 RPM.
3. The ECM driver transitions from ON to OFF or from OFF to ON.

1. A short to ground on the A/C compressor clutch relay control circuit
2. A short to voltage on the A/C compressor clutch relay control circuit
3. An open circuit on the A/C compressor clutch relay control circuit or relay
4. An internally shorted or excessively low resistance A/C clutch relay coil

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.

Schematic Reference

HVAC Schematics

Connector End View Reference

Component Connector End Views

Description and Operation

1. «Air Delivery Description and Operation»(/cadillac/dts/i-2005-2011/remont/automatic-hvac-system/#hvac-system-automatic__air-delivery-description-operation)
2. «Air Temperature Description and Operation»(/cadillac/dts/i-2005-2011/remont/automatic-hvac-system/#hvac-system-automatic__air-temperature-description-operation)

Electrical Information Reference

1. «Circuit Testing»(/cadillac/dts/i-2005-2011/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-service-troubleshooting-diagnosis__circuit-testing)
2. «Connector Repairs»(/cadillac/dts/i-2005-2011/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-service-troubleshooting-diagnosis__connector-repairs)
3. «Testing for Intermittent Conditions and Poor Connections»(/cadillac/dts/i-2005-2011/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-service-troubleshooting-diagnosis__testing-for-intermittent-conditions-poor)
4. «Wiring Repairs»(/cadillac/dts/i-2005-2011/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-service-troubleshooting-diagnosis__wiring-repairs)

Scan Tool Reference

Control Module References for scan tool information

1. Ignition OFF, disconnect the A/C relay.
2. Ignition ON, verify that a test lamp does not illuminate between the control circuit terminal 86 and ground. If the test lamp illuminates, test the control circuit for a short to voltage.
3. Verify that a test lamp illuminates between the ignition circuit terminal 85 and ground. If the test lamp does not illuminate, test the ignition circuit for a short to ground or a open/high resistance. If the circuit tests normal and ignition circuit fuse is open, test all components connected to the ignition circuit and replace as necessary.
4. Verify that a test lamp illuminates between the relay B+ circuit terminal 30 and ground. If the test lamp does not illuminate, test the B+ circuit for a short to ground or a open/high resistance. If the circuit tests normal and B+ circuit fuse is open, replace the A/C clutch relay.
5. Disconnect the harness connector at the A/C clutch coil.
6. Test for less than 1 ohm between the ground circuit terminal 2 and ground. If greater than the specified range, test the ground circuit for an open/high resistance.
7. Connect the harness connector at the A/C clutch coil.
8. Connect a 10-amp fused jumper wire between the B+ circuit terminal 30 and control circuit terminal 87. Verify the A/C clutch is activated. If the A/C clutch does not activate, test the control circuit for an open/high resistance. If the circuit tests normal, test or replace the A/C clutch.
9. Connect a test lamp between the ignition circuit terminal 85 and the control circuit terminal 86.
10. Command the A/C relay output function ON and OFF with a scan tool. The test lamp should turn ON and OFF when changing between the commanded states. If the test lamp is always ON, test the control circuit for a short to ground. If the circuit tests normal, replace the ECM. If the test lamp is always OFF, test the control circuit for a short to voltage, or an open/high resistance. If the circuit tests normal, replace the ECM.
11. If all circuits test normal, test or replace the A/C clutch relay.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

1. «Relay Replacement (Attached to Wire Harness)»(/cadillac/dts/i-2005-2011/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-introduction) or «Relay Replacement (Within an Electrical Center)»(/cadillac/dts/i-2005-2011/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-introduction)
2. «Control Module References»(/cadillac/dts/i-2005-2011/remont/communication-devices/#programming-and-setup-all-systems__control-module-references) for ECM replacement, setup, and programming

Symptoms - HVAC Systems - Automatic

Visual/Physical Inspection

1. Inspect for aftermarket devices which could affect the operation of the HVAC System. Refer to «Checking Aftermarket Accessories»(/cadillac/dts/i-2005-2011/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-service-troubleshooting-diagnosis__checking-aftermarket-accessories) .
2. Inspect the easily accessible or visible system components for obvious damage or conditions which could cause the symptom.
3. Verify the A/C compressor clutch turns freely and is not seized.
4. The A/C compressor will not operate in cold outside air temperatures. Refer to «Air Temperature Description and Operation»(/cadillac/dts/i-2005-2011/remont/automatic-hvac-system/#hvac-system-automatic__air-temperature-description-operation) .
5. The following could cause window fogging: Wet carpet or mats High humidity Interior water leak Blocked A/C evaporator drain tube Maximum passenger capacity Blocked body pressure relief valves
6. Inspect the air distribution system for causes of reduced air flow: Obstructed or dirty passenger compartment air filter, if equipped Blocked or damaged air inlet or outlet vents

Intermittent

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

Symptom List

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

1. «Blower Motor Malfunction»(/cadillac/dts/i-2005-2011/remont/automatic-hvac-system/#hvac-system-automatic)
2. «Auxiliary Blower Motor Malfunction»(/cadillac/dts/i-2005-2011/remont/automatic-hvac-system/#hvac-system-automatic)
3. «Air Conditioning Compressor Malfunction»(/cadillac/dts/i-2005-2011/remont/automatic-hvac-system/#hvac-system-automatic)
4. «Air Temperature Malfunction»(/cadillac/dts/i-2005-2011/remont/automatic-hvac-system/#hvac-system-automatic)
5. «Leak Testing»(/cadillac/dts/i-2005-2011/remont/automatic-hvac-system/#heating-ventilation-and-air-conditioning__leak-testing)
6. «Noise Diagnosis - HVAC Module»(/cadillac/dts/i-2005-2011/remont/automatic-hvac-system/#heating-ventilation-and-air-conditioning__noise-diagnosis-hvac-module)
7. «Noise Diagnosis - Air Conditioning (A/C) System»(/cadillac/dts/i-2005-2011/remont/automatic-hvac-system/#heating-ventilation-and-air-conditioning__noise-diagnosis-air-conditioning-ac)
8. «Noise Diagnosis - Blower Motor»(/cadillac/dts/i-2005-2011/remont/automatic-hvac-system/#heating-ventilation-and-air-conditioning__noise-diagnosis-blower-motor)
9. «Odor Diagnosis»(/cadillac/dts/i-2005-2011/remont/automatic-hvac-system/#heating-ventilation-and-air-conditioning__odor-diagnosis)

1. Perform the «Diagnostic System Check - Vehicle»(/cadillac/dts/i-2005-2011/remont/oem-general-information/#vehicle-diagnostic-information__diagnostic-system-check-vehicle) prior to using this diagnostic procedure.
2. Review «Strategy Based Diagnosis»(/cadillac/dts/i-2005-2011/remont/oem-general-information/#vehicle-diagnostic-information__strategy-based-diagnosis) for an overview of the diagnostic approach.
3. «Diagnostic Procedure Instructions»(/cadillac/dts/i-2005-2011/remont/oem-general-information/#vehicle-diagnostic-information__diagnostic-procedure-instructions) provides an overview of each diagnostic category.

When the A/C switch is pressed, the HVAC control assembly sends a serial data message to the engine control module (ECM) for an A/C request. This input will request the ECM to ground the A/C compressor clutch relay control circuit, which will switch the A/C CLTCH relay. With the relay contacts closed, battery voltage is supplied to the A/C compressor clutch assembly.

The following conditions must be met in order for the ECM to turn on the compressor clutch

1. Battery voltage is between 9-18 volts.
2. Engine coolant temperature (ECT) is less than 123°C (253°F).
3. Engine speed is less than 4,760 RPM.
4. Engine speed is more than 600 RPM.
5. A/C high side pressure is between 3102-193 kPa (450-28 psi).
6. Throttle position is less than 100 percent.
7. Evaporator temperature is greater than 2°C (35°F).
8. Ambient air temperature is greater than 2°C (35°F).
9. ECM does not detect excessive torque load.
10. ECM does not detect insufficient idle quality.

Schematic Reference

HVAC Schematics

Connector End View Reference

Component Connector End Views

Description and Operation

Air Temperature Description and Operation

Electrical Information Reference

1. «Circuit Testing»(/cadillac/dts/i-2005-2011/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-service-troubleshooting-diagnosis__circuit-testing)
2. «Connector Repairs»(/cadillac/dts/i-2005-2011/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-service-troubleshooting-diagnosis__connector-repairs)
3. «Testing for Intermittent Conditions and Poor Connections»(/cadillac/dts/i-2005-2011/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-service-troubleshooting-diagnosis__testing-for-intermittent-conditions-poor)
4. «Wiring Repairs»(/cadillac/dts/i-2005-2011/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-service-troubleshooting-diagnosis__wiring-repairs)

Scan Tool Reference

Control Module References for scan tool information

1. Ignition OFF, disconnect the A/C relay.
2. Ignition ON, verify that a test lamp does not illuminate between the control circuit terminal 86 and ground. If the test lamp illuminates, test the control circuit for a short to voltage.
3. Verify that a test lamp illuminates between the ignition circuit terminal 85 and ground. If the test lamp does not illuminate, test the ignition circuit for a short to ground or a open/high resistance. If the circuit tests normal and ignition circuit fuse is open, test all components connected to the ignition circuit and replace as necessary.
4. Verify that a test lamp illuminates between the relay B+ circuit terminal 30 and ground. If the test lamp does not illuminate, test the B+ circuit for a short to ground or a open/high resistance. If the circuit tests normal and B+ circuit fuse is open, replace the A/C clutch relay.
5. Disconnect the harness connector at the A/C clutch coil.
6. Test for less than 1 ohm between the ground circuit terminal 2 and ground. If greater than the specified range, test the ground circuit for an open/high resistance.
7. Connect the harness connector at the A/C clutch coil.
8. Connect a 10-amp fused jumper wire between the B+ circuit terminal 30 and control circuit terminal 87. Verify the A/C clutch is activated. If the A/C clutch does not activate, test the control circuit for an open/high resistance. If the circuit tests normal, test or replace the A/C clutch.
9. Connect a test lamp between the ignition circuit terminal 85 and the control circuit terminal 86.
10. Command the A/C relay output function ON and OFF with a scan tool. The test lamp should turn ON and OFF when changing between the commanded states. If the test lamp is always ON, test the control circuit for a short to ground. If the circuit tests normal, replace the ECM. If the test lamp is always OFF, test the control circuit for a short to voltage, or an open/high resistance. If the circuit tests normal, replace the ECM.
11. If all circuits test normal, test or replace the A/C clutch relay.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

1. «Air Conditioning Compressor Replacement»(/cadillac/dts/i-2005-2011/remont/automatic-hvac-system/#heating-ventilation-and-air-conditioning)
2. «Control Module References»(/cadillac/dts/i-2005-2011/remont/communication-devices/#programming-and-setup-all-systems__control-module-references) for HVAC control module and ECM replacement, setup, and programming

1. Perform the «Diagnostic System Check - Vehicle»(/cadillac/dts/i-2005-2011/remont/oem-general-information/#vehicle-diagnostic-information__diagnostic-system-check-vehicle) prior to using this diagnostic procedure.
2. Review «Strategy Based Diagnosis»(/cadillac/dts/i-2005-2011/remont/oem-general-information/#vehicle-diagnostic-information__strategy-based-diagnosis) for an overview of the diagnostic approach.
3. «Diagnostic Procedure Instructions»(/cadillac/dts/i-2005-2011/remont/oem-general-information/#vehicle-diagnostic-information__diagnostic-procedure-instructions) provides an overview of each diagnostic category.

Blower Motor Control Module

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 pulse width modulation (PWM) signal to the blower motor control module 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.

Schematic Reference

HVAC Schematics

Connector End View Reference

Component Connector End Views

Description and Operation

Air Delivery Description and Operation

Electrical Information Reference

1. «Circuit Testing»(/cadillac/dts/i-2005-2011/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-service-troubleshooting-diagnosis__circuit-testing)
2. «Connector Repairs»(/cadillac/dts/i-2005-2011/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-service-troubleshooting-diagnosis__connector-repairs)
3. «Testing for Intermittent Conditions and Poor Connections»(/cadillac/dts/i-2005-2011/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-service-troubleshooting-diagnosis__testing-for-intermittent-conditions-poor)
4. «Wiring Repairs»(/cadillac/dts/i-2005-2011/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-service-troubleshooting-diagnosis__wiring-repairs)

Scan Tool Reference

Control Module References for scan tool information

1. Ignition ON, switch the climate control system to the manual setting. Turn the fan speed control knob from the lowest to highest setting. The blower motor speed should change between commanded states.
2. Turn the blower speed control knob to the "O" position. The blower motor should turn OFF.

1. Ignition OFF, disconnect the harness connector at the blower motor control module connector X2.
2. Test for less than 1.0 ohm between the ground circuit connector X2 terminal 5 and ground. If greater than the specified range, test the ground circuit for an open/high resistance.
3. Ignition ON, verify that a test lamp illuminates between the B+ circuit of the blower motor speed control module supply voltage connector X2 terminal 6 and ground. If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance. If the circuit tests normal and the B+ circuit fuse (HVAC BLWR 40-amp) in the underhood fuse block is open, test all components connected to the B+ circuit and replace as necessary.
4. Connect a test lamp between the blower motor speed control circuit connector X2 terminal 3 and the blower motor supply voltage circuit connector X2 terminal 6 of the blower motor control module.
5. Turn the blower motor ON and then OFF. The test lamp should turn ON and OFF when changing between the commanded states. If the test lamp is always ON, test the control circuit for a short to ground. If the circuit tests normal, replace the HVAC control module. If the test lamp is always OFF, test the speed control circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the HVAC control module.
6. Ignition OFF, reconnect the harness connector X2 at the blower motor control module.
7. Disconnect the harness connector at the blower motor.
8. Ignition ON, verify that a test lamp illuminates between the blower motor supply voltage circuit terminal A of the blower motor control module and ground. If the test lamp does not illuminate, test the blower motor supply voltage circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the blower motor control module.
9. Connect a test lamp between the blower motor speed circuit terminal B and the blower motor ground circuit terminal A of the blower motor control module.
10. Turn the blower motor on high speed then to low speed. The test lamp intensity should be bright when in high speed and very dim or out when the blower is on low speed. If the test lamp intensity is not correct, test the blower motor ground circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the blower motor control module.
11. If all circuits test normal, replace the blower motor.

Component Testing

Blower Motor

1. Ignition OFF, disconnect the harness at the blower motor.
2. Install a 40-amp fused jumper wire between circuit terminal 1 and 12 volts. Install a jumper wire between the low reference circuit terminal 2 and ground. Verify the blower motor activates If the blower motor does not activate, replace the blower motor.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

1. «Blower Motor Replacement»(/cadillac/dts/i-2005-2011/remont/automatic-hvac-system/#heating-ventilation-and-air-conditioning)
2. «Control Module References»(/cadillac/dts/i-2005-2011/remont/communication-devices/#programming-and-setup-all-systems__control-module-references) for blower motor control module and HVAC control module replacement, setup, and programming

1. Perform the «Diagnostic System Check - Vehicle»(/cadillac/dts/i-2005-2011/remont/oem-general-information/#vehicle-diagnostic-information__diagnostic-system-check-vehicle) prior to using this diagnostic procedure.
2. Review «Strategy Based Diagnosis»(/cadillac/dts/i-2005-2011/remont/oem-general-information/#vehicle-diagnostic-information__strategy-based-diagnosis) for an overview of the diagnostic approach.
3. «Diagnostic Procedure Instructions»(/cadillac/dts/i-2005-2011/remont/oem-general-information/#vehicle-diagnostic-information__diagnostic-procedure-instructions) provides an overview of each diagnostic category.

Auxiliary HVAC Control Module

The front HVAC control module must be in the ON position for GMLAN communication to allow the rear HVAC control module to operate.

Auxiliary Blower Motor Control Module

The following are auxiliary blower motor control module circuits

1. Rear blower motor speed control circuit-When the auxiliary blower switch is placed in any speed position this circuit is a pulse width modulated signal that is sent from the Auxiliary HVAC control module to the auxiliary blower motor control module.
2. Ground-A constant body ground is supplied to the auxiliary blower motor control module.
3. Low reference-This circuit is grounded through the auxiliary blower motor control module only when the auxiliary HVAC control module is in high speed. In all other blower speeds this circuit is a pulse width modulated signal (PWM). The longer this circuit is pulsed the ground the faster the blower speed will be.
4. Blower speed feed back signal-This feedback circuit displays in percent on the TECH 2 the commanded output blower speed that the auxiliary blower motor control module is sending to the auxiliary blower motor.

Auxiliary Blower Motor

The following are auxiliary blower motor circuits

1. Ground-A constant body ground is supplied the blower motor.
2. Ignition voltage-Ignition voltage is supplied to the blower motor from the rear fuse box.
3. Low reference-This circuit is grounded through the auxiliary blower motor control module only when the auxiliary HVAC control module is in high speed. In all other blower speeds this circuit is a pulse width modulated signal (PWM). The longer this circuit is pulsed the ground the faster the blower speed will be.

Schematic Reference

HVAC Schematics

Connector End View Reference

Component Connector End Views

Description and Operation

Air Delivery Description and Operation

Electrical Information Reference

1. «Circuit Testing»(/cadillac/dts/i-2005-2011/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-service-troubleshooting-diagnosis__circuit-testing)
2. «Connector Repairs»(/cadillac/dts/i-2005-2011/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-service-troubleshooting-diagnosis__connector-repairs)
3. «Testing for Intermittent Conditions and Poor Connections»(/cadillac/dts/i-2005-2011/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-service-troubleshooting-diagnosis__testing-for-intermittent-conditions-poor)
4. «Wiring Repairs»(/cadillac/dts/i-2005-2011/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-service-troubleshooting-diagnosis__wiring-repairs)

Scan Tool Reference

Control Module References for scan tool information

1. Ignition OFF, disconnect the auxiliary blower motor.
2. Test for less than 1 ohm of resistance between the ground circuit terminal 2 and ground. If greater than 1 ohm, test the ground circuit for an open/high resistance.
3. Ignition ON, verify that a test lamp illuminates between the B+ circuit terminal 1 and ground. If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance. If the circuit tests normal and the B+ circuit fuse is open, replace the aux blower motor.
4. Ignition OFF, disconnect the harness connector at the auxiliary blower motor control module.
5. Ignition ON, verify that a test lamp does not illuminates between the control circuit terminal 4 and ground. If test lamp illuminates, test the control circuit for a short to voltage.
6. Test for less than 1 ohm of resistance between the ground circuit terminal 2 and ground. If greater than 1 ohm, test the ground circuit for an open/high resistance.
7. Connect the auxiliary blower motor connector.
8. Ignition ON, verity that a test lamp illuminates between the control circuit terminal 4 and ground. If test lamp does not illuminate, test the control circuit for a short to ground or an open/high resistance. If circuit test normal replace auxiliary blower motor.
9. Select the AUTO position on the front HVAC module.
10. Test for 12-27 Mv between the control circuit terminal 1 and ground while adjusting the rear auxiliary HVAC control module blower from 1 to 4 bars. If less than 12 Mv, test the control circuit for a short to ground or an open/high resistance. If the circuit tests normal replace the rear auxiliary HVAC module. If greater than 27 Mv, test the control circuit for a short to voltage. If the circuit tests normal replace the rear auxiliary HVAC module.
11. Test for above 10 volts while adjusting the rear auxiliary HVAC blower switch to 5 bars. If less than 10 volts replace the rear auxiliary HVAC control module.
12. Select the AUTO position on the rear auxiliary HVAC control module.
13. Test for 12-145 Mv between the control circuit terminal 1 and ground while adjusting the front HVAC control module blower from low speed to high speed. If less than 12 Mv, replace the front HVAC control module. If greater than 145 Mv, replace the front HVAC control module.
14. Place the front and rear HVAC modules in low speed.
15. Test for 0.2--15 Mv between the signal circuit terminal 3 and ground. If less than 0.2 Mv, test the signal circuit for a short to ground or an open high resistance. If the circuit tests normal replace the rear auxiliary HVAC module. If greater than 15 Mv, test the signal circuit for a short to voltage. If the circuit tests normal replace the rear auxiliary HVAC module.
16. If all circuits test normal, replace the auxiliary blower motor control module.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

1. «Auxiliary Blower Motor Replacement»(/cadillac/dts/i-2005-2011/remont/automatic-hvac-system/#heating-ventilation-and-air-conditioning)
2. «Control Module References»(/cadillac/dts/i-2005-2011/remont/communication-devices/#programming-and-setup-all-systems__control-module-references) for HVAC Control Module or Auxiliary HVAC replacement, setup and programming

1. Perform the «Diagnostic System Check - Vehicle»(/cadillac/dts/i-2005-2011/remont/oem-general-information/#vehicle-diagnostic-information__diagnostic-system-check-vehicle) prior to using this diagnostic procedure.
2. Review «Strategy Based Diagnosis»(/cadillac/dts/i-2005-2011/remont/oem-general-information/#vehicle-diagnostic-information__strategy-based-diagnosis) for an overview of the diagnostic approach.
3. «Diagnostic Procedure Instructions»(/cadillac/dts/i-2005-2011/remont/oem-general-information/#vehicle-diagnostic-information__diagnostic-procedure-instructions) provides an overview of each diagnostic category.

Evaporator, Inside & Ambient Air Temperature Sensors

The HVAC control module supplies the evaporator, inside and ambient air temperature sensors with a low reference circuit and 5-volt signal circuit. The HVAC control module determines the voltage drop across the sensors. As the air temperature increases, the sensor resistance decreases and the voltage signal decreases. As the air temperature decreases, the sensor resistance increases and the voltage signal increases.

Sunload Sensor Assembly

The sunload sensor is a 2-wire photo diode. Body ground and 5-volt 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 very bright. The sunload sensor provides the HVAC control module with a measurement of the amount of light shining on the vehicle. Bright or high intensity light causes the vehicle interior temperature to increase. The HVAC system compensates for the increased temperature by diverting additional cool air into the vehicle.

Schematic Reference

HVAC Schematics

Connector End View Reference

Component Connector End Views

Description and Operation

1. «Air Temperature Description and Operation»(/cadillac/dts/i-2005-2011/remont/automatic-hvac-system/#hvac-system-automatic__air-temperature-description-operation)
2. «Air Delivery Description and Operation»(/cadillac/dts/i-2005-2011/remont/automatic-hvac-system/#hvac-system-automatic__air-delivery-description-operation)

Electrical Information Reference

1. «Circuit Testing»(/cadillac/dts/i-2005-2011/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-service-troubleshooting-diagnosis__circuit-testing)
2. «Connector Repairs»(/cadillac/dts/i-2005-2011/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-service-troubleshooting-diagnosis__connector-repairs)
3. «Testing for Intermittent Conditions and Poor Connections»(/cadillac/dts/i-2005-2011/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-service-troubleshooting-diagnosis__testing-for-intermittent-conditions-poor)
4. «Wiring Repairs»(/cadillac/dts/i-2005-2011/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-service-troubleshooting-diagnosis__wiring-repairs)

Scan Tool Reference

Control Module References for scan tool information

1. Ignition ON, cover the sunload sensor assembly with a shop towel or other suitable item. Verify the scan tool Right Sunload Sensor and Left Sunload Sensor parameters are within 3 counts of each other. If not within the specified range, refer to «Sunload Sensor Circuit Malfunction»(/cadillac/dts/i-2005-2011/remont/automatic-hvac-system/#hvac-system-automatic) .
2. 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 «Evaporator and Ambient Air Temperature Sensor Circuit Malfunction»(/cadillac/dts/i-2005-2011/remont/automatic-hvac-system/#hvac-system-automatic) .
3. Measure actual inside air temperature using a thermometer. Compare this value to the scan tool Inside Air Temp. parameter. The measured temperature should be within 5 degrees of parameter. If not within the specified range, refer to «Inside Air Temperature Sensor Circuit Malfunction»(/cadillac/dts/i-2005-2011/remont/automatic-hvac-system/#hvac-system-automatic) .
4. Measure actual evaporator air temperature using a thermometer. Compare this value to the scan tool A/C Evap. Temperature Sensor parameter. The measured temperature should be within 5 degrees of the parameter. If not within the specified range, refer to «Evaporator and Ambient Air Temperature Sensor Circuit Malfunction»(/cadillac/dts/i-2005-2011/remont/automatic-hvac-system/#hvac-system-automatic) .

Evaporator and Ambient Air Temperature Sensor Circuit Malfunction

1. Ignition OFF, disconnect the harness connector at the appropriate temperature sensor.
2. Ignition OFF, test for less than 10 ohms between the low reference circuit terminal B and ground. If greater than the specified range, test the low reference circuit for high resistance. If the circuit tests normal, replace the HVAC control module.
3. Ignition ON, test for 4.8-5.2 volts between the low reference circuit terminal B and the signal circuit terminal A. If less than the specified range, test the signal circuit for high resistance. If the circuit tests normal, replace the HVAC control module.
4. If all circuits test normal, test or replace the temperature sensor.

Sunload Sensor Circuit Malfunction

1. Ignition OFF, disconnect the harness connector at the sunload sensor.
2. Ignition OFF, test for less than 10 ohms between the ground circuit terminal C and ground. If greater than the specified range, test the ground circuit for high resistance.
3. Ignition ON, test for 4.8-5.2 volts between the ground circuit terminal C and the appropriate signal circuit terminal. Left sunload sensor circuit terminal A Right sunload sensor circuit terminal B If less than the specified range, test the signal circuit for high resistance. If the circuit tests normal, replace the HVAC control module.
4. If all circuits test normal, test or replace the sunload sensor.

Inside Air Temperature Sensor Circuit Malfunction

1. Ignition OFF, disconnect the harness connector at the inside air temperature sensor.
2. Ignition OFF, test for less than 10 ohms between the ground circuit terminal C and ground. If greater than the specified range, test the ground circuit for high resistance.
3. Ignition OFF, test for less than 10 ohms between the low reference circuit terminal D and ground. If greater than the specified range, test the low reference circuit for high resistance. If the circuit tests normal, replace the HVAC control module.
4. Ignition ON, HVAC control module ON. Verify that a test lamp illuminates between the ground circuit terminal C and the control circuit terminal B. If the test lamp does not illuminate, test the control circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the HVAC control module.
5. Ignition ON, test for 4.8-5.2 volts between the low reference circuit terminal D and the signal circuit terminal A. If less than the specified range, test the signal circuit for high resistance. If the circuit tests normal, replace the HVAC control module.
6. If all circuits test normal, test or replace the inside air temperature sensor.

1. A thermometer can be used to test the sensor off the vehicle in warn and or cold water. Refer to «Sensor Resistance Table»(/cadillac/dts/i-2005-2011/remont/automatic-hvac-system/#hvac-system-automatic__sensor-resistance-table) for this test.
2. Test the air temperature sensor by varying the sensor temperature while monitoring the sensor resistance.
3. Compare the readings with the Temperature VS Resistance table and verify that the resistance is within 5 percent of the specification. If not within the specified range, replace the sensor.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

1. «Ambient Air Temperature Sensor Replacement»(/cadillac/dts/i-2005-2011/remont/automatic-hvac-system/#hvac-system-automatic)
2. «Inside Air Temperature Sensor Replacement»(/cadillac/dts/i-2005-2011/remont/automatic-hvac-system/#hvac-system-automatic)
3. «Sun Load Sensor Replacement»(/cadillac/dts/i-2005-2011/remont/automatic-hvac-system/#hvac-system-automatic)
4. «Heater and Air Conditioning Control Wiring Harness Replacement (w/Evaporator Temperature Sensor)»(/cadillac/dts/i-2005-2011/remont/automatic-hvac-system/#hvac-system-automatic)
5. «Control Module References»(/cadillac/dts/i-2005-2011/remont/communication-devices/#programming-and-setup-all-systems__control-module-references) for HVAC control module replacement, setup, and programming

Afterblow Enabling

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) .

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 32 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 instrument panel (I/P) accessory trim plate. Refer to «Instrument Panel Cluster Trim Plate Bezel Replacement»(/cadillac/dts/i-2005-2011/remont/exteriorinterior-trim/#instrument-panel-trim-and-console-trim) or «Instrument Panel Accessory Trim Plate Replacement - Left Side»(/cadillac/dts/i-2005-2011/remont/exteriorinterior-trim/#instrument-panel-trim-and-console-trim) .
2. Remove the HVAC control module assembly screws.
3. Disconnect the electrical connectors from the HVAC control module assembly.

Installation Procedure

1. Connect the electrical connectors to the HVAC control module assembly.
2. Install the HVAC control module assembly into the I/P.
3. Install the HVAC control module assembly screws. Tighten: Tighten the screws to 1.9 N.m (17 lb in).
4. Install the I/P accessory trim plate. Refer to «Instrument Panel Cluster Trim Plate Bezel Replacement»(/cadillac/dts/i-2005-2011/remont/exteriorinterior-trim/#instrument-panel-trim-and-console-trim) or «Instrument Panel Accessory Trim Plate Replacement - Left Side»(/cadillac/dts/i-2005-2011/remont/exteriorinterior-trim/#instrument-panel-trim-and-console-trim) .
5. Refer to «Control Module References»(/cadillac/dts/i-2005-2011/remont/communication-devices/#programming-and-setup-all-systems__control-module-references) for replacement and setup information.

1. Using a flat-bladed tool, carefully pry out on the top of the HVAC control - auxiliary.
2. Remove the HVAC control - auxiliary from the center console.
3. Disconnect the electrical connector.
4. Remove the HVAC control - auxiliary.

1. Connect the HVAC control - auxiliary electrical connector.
2. Install the HVAC control - auxiliary in the console bottom first.
3. Push in at the top of the HVAC control - auxiliary in order to engage the HVAC control - auxiliary in the console.
4. Refer to «Control Module References»(/cadillac/dts/i-2005-2011/remont/communication-devices/#programming-and-setup-all-systems__control-module-references) for replacement and setup information.

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Air Delivery Description & Operation

The Air Delivery Description and Operation is divided into 6 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 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 HVAC control module uses for keep alive memory (KAM). The body control module (BCM), which is the vehicle power mode master, provides a device on signal. The control module supports the following features

Remote Start & Personalization

When the Remote Start feature is activated through the key FOB, it starts up the vehicles automatic HVAC control system according to the previous settings of the system before turning the vehicle off. When the outside temperature is cold, the automatic HVAC control system will start up the rear window defogger and if the vehicle has heated seats, they will also turn on. Cooled seat are activated during a remote start. Normal operation of the automatic HVAC control system will return after the key is turned to RUN position.

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 Remote Keyless Entry via GMLAN. 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 speed level. When OnStar® audio control is active, the blower control runs the fan at a reduced speed to enable audio communications. This ensures 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.

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 vehicles interior. The vehicle operator determines the blower motors speed by placing the blower knob dial in a desired speed position or by selecting automatic operation. In manual operation, the blower has six speed selections. The HVAC control module may alter the blower motor speed due to compensating factors. In automatic operation, the HVAC control module will determine what blower speed is necessary in order to achieve or maintain a desired temperature. In manual and automatic operation, the blower speed temporarily reduces speed during transition between outlet modes.

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) .

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 22°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 will repeat step 1 and 2 above for 2 more cycles.

Air Distribution

The HVAC control module controls the mode actuator in order to distribute airflow to a desired outlet. The mode knob 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 or defog. When the mode is in floor, recirculation will only be available for 3 minutes. If the system is in full (100%) recirculation continuously for more than 20 minutes, the recirculation actuator moves to a 95% recirculation door position. The HVAC control module will prevent the system from returning to the full recirculation position until the next ignition cycle. 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 requesting 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 on both knobs.

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 setting 90°F is selected in automatic operation, the blower speed will increase gradually to the maximum speed. Temperature actuators will be in full heat position, mode actuators will be in floor position while maintaining 90°F temperature setting. 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 setting 60°F 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 panel position and the recirculation actuator will remain in RECIRC 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.

The auxiliary HVAC control module is a GMLAN device that interfaces between the operator, the front HVAC control module, and the auxiliary HVAC system to maintain air temperature and air distribution settings. Battery power, ground, and LED dimming 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. The rear HVAC control module is powered ON or OFF through GMLAN communication of vehicle power-mode.

The rear control can be turned ON and OFF by pressing the AUX button on the front HVAC control module. The rear control can also be turned ON by pressing any rocker button on the control head. Pressing the fan blower rocker button down will eventually turn off the control head.

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. 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 & 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 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 HVAC control module uses for keep alive memory (KAM). The body control module (BCM), which is the vehicle power mode master, provides a device on signal. The control module supports the following features

When the Remote Start feature is activated through the key FOB, it starts up the vehicles automatic HVAC control system according to the previous settings of the system before turning the vehicle off. When the outside temperature is cold, the automatic HVAC control system will start up the rear window defogger and if the vehicle has heated seats, they will also turn on. Cooled seat are activated during a remote start. Normal operation of the automatic HVAC control system will return after the key is turned to RUN position.

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 Remote Keyless Entry via GMLAN. 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

During OnStar® audio control ON, the HVAC control module receives signals from OnStar® to reduce blower speed level. When OnStar® audio control is active, the blower control runs the fan at a reduced speed to enable audio communications. This ensures 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 driver air temperature actuator is a reverse polarity motor. The control circuits use either a 0 or 12-volt value to coordinate the actuator movement. When the actuator is at rest, both control circuits have a value of 0 volts. In order to move the actuator, the HVAC control module grounds one of the control circuits while providing the other with 12 volts. The HVAC control module reverses the polarity of the control circuits to move the actuator in the opposite direction. When the actuator shaft rotates, the potentiometers adjustable contact changes the door position signal between 0-5 volts. The HVAC control module uses a range of 0-255 counts to index the actuator position. The door position signal voltage is converted to a 0-255 count range. When the module sets a commanded, or targeted value, one of the control circuits is grounded. As the actuator shaft rotates the changing position signal is sent to the module. Once the position signal and the commanded value are the same, the module removes power and ground from the control circuits.

Air Temperature 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 -40°C to +150°C. 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 -40°C to +125°C (-40°F to +257°F). If the HVAC control module has determined that the ambient temperature sensor has failed, the driver information center (DIC) display shall display (-°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 sensor reading when the vehicle is turned on less than the sensor reading before the vehicle was turned off, 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 16 km/h (10 mph), the ambient air temperature displayed may be allowed to increase, but only at a slow, filtered rate. The HVAC control module displays the ambient air temperature value. 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 while holding down the Left Temperature Up and the PASS enable button, press the Rear Defog button.

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 sunlight causes the vehicles inside temperature to increase. The HVAC system compensates for the increased temperature by diverting additional cool air into the vehicle. If the sensor is open or shorted, no sunload adjustment occurs and the SERVICE A/C SYSTEM message is displayed in the instrument panel cluster (IPC).

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 backside of 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 GMLAN message to the engine control module (ECM) to stop requesting the A/C compressor clutch operation if the temperature drops below -4°C (25°F). The sensor must be above 2°C (36°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 GMLAN message sent to the ECM will not submit the A/C ON request. The HVAC control module will then send a request to instrument panel for display of the SERVICE A/C SYSTEM that will be displayed on the DIC. The HVAC control module will also turn off the A/C LED on the HVAC control module as long as the condition is present, if the A/C button is pushed the LED will flash 3 times and remain OFF.

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 GMLAN message sent to the HVAC control module will be invalid. The HVAC control module will then send a request to the IPC for display of the SERVICE A/C SYSTEM that will be displayed on the DIC. The HVAC control module will also turn off A/C OFF LED display on the HVAC control module as long as the condition is present, if the A/C button is pushed the LED will flash 3 times and remain OFF.

Heating & 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 evaporator 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 Water temperature Evaporator 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 (25°F) Control module operating range 9-16 volts
2. ECM Engine coolant temperature (ECT) is less than 125°C (257°F). A/C pressure is between 3 137 kPa (455 psi) and 210 kPa (210 psi).

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

1. Throttle position is 90 percent.
2. A/C pressure is more than 3 137 kPa (455 psi).
3. A/C pressure is less than 193 kPa (28 psi).
4. ECT is more than 125°C (257°F).
5. Transmission shift
6. ECM detects excessive torque load.
7. ECM detects insufficient idle quality.
8. 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 and rear seat temperature actuators. The passenger and rear setting cannot be used without the driver setting also being ON. The passenger setting can be turned ON by pressing the PASS button or the passenger colder and warmer buttons, to turn off press the PASS button. The rear control can be turned ON and OFF using the front HVAC control module. The rear control can also be turned ON by touching any rocker button on the control head, the fan blower rocker button when going down in blower speed will turn OFF the control head. 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 HVAC 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 actuator.

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 knob 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 setting 90°F is selected in automatic operation, the blower speed will increase gradually, to the maximum speed. Temperature actuators will be in full heat position, mode actuators will be in floor position while maintaining 90°F temperature setting. 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 setting 60°F 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 panel position and the recirculation actuator will remain in RECIRC 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 GMLAN device that interfaces between the operator, the front HVAC control module and the Aux. HVAC system to maintain air temperature and air distribution settings. Battery voltage, ground and LED dimming are supplied to the Aux. 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 Aux. HVAC control module on which position to place the actuator. The Aux. HVAC control module is powered ON or OFF through GMLAN communication by the vehicle power-mode.

Auxiliary Heating & 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 either 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.

Steering Wheel Controls

The HVAC control module receives GMLAN 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 . 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

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

Scheme 64

See also:
• Diagnostic System Check - Vehicle
• Strategy Based Diagnosis
• Diagnostic Procedure Instructions
• Component Connector End Views
• Circuit Testing
• Connector Repairs
• Testing for Intermittent Conditions and Poor Connections
• Wiring Repairs
• Control Module References
• Diagnostic Repair Verification
• Air Conditioning (A/C) Refrigerant Pressure Sensor Replacement
• Relay Replacement (Attached to Wire Harness)
• Checking Aftermarket Accessories
• Leak Testing
• Noise Diagnosis - HVAC Module
• Noise Diagnosis - Air Conditioning (A/C) System
• Noise Diagnosis - Blower Motor
• Odor Diagnosis
• Service Programming System (SPS)
• Instrument Panel Cluster Trim Plate Bezel Replacement
• Fastener Notice
• Fastener Tightening Specifications
• Front Compartment Sight Shields Replacement
• Radio/Audio System Description and Operation
• DTC B0158
• Air Delivery Description and Operation
• Air Temperature Description and Operation
• Sensor Resistance Table
• Fastener Tightening Specifications