HVAC System - Automatic Cadillac STS I рестайлинг

Fastener Tightening Specifications

Sensor Resistance Table

Scheme 17

Scheme 18

Scheme 19

Scheme 20

Scheme 21

DIAGNOSTIC CODE INDEX

DIAGNOSTIC CODE INDEX

Diagnostic Instructions

1. Perform the «Diagnostic System Check - Vehicle»(/cadillac/sts/i-2007-2011/remont/oem-general-information/#vehicle-diagnostic-information-2-of-2) prior to using this diagnostic procedure.
2. Review «Strategy Based Diagnosis»(/cadillac/sts/i-2007-2011/remont/oem-general-information/#vehicle-diagnostic-information-2-of-2__strategy-based-diagnosis) for an overview of the diagnostic approach.
3. «Diagnostic Procedure Instructions»(/cadillac/sts/i-2007-2011/remont/oem-general-information/#vehicle-diagnostic-information-2-of-2__diagnostic-procedure-instructions) provides an overview of each diagnostic category.

Diagnostic Fault Information

Circuit Description

The HVAC control module monitors the outside air quality via the air quality sensor assembly while in AUTO mode. The air quality sensor is a 5-wire sensor with a single ignition voltage circuit, a ground circuit, a low reference circuit, and two signal circuits. There are 2 sensors inside the air quality sensor assembly. A hydrocarbon (HC) sensor which is used for detecting gasoline exhaust fumes and a NOX sensor which is used for detecting oxides of nitrogen. When high levels of HC are detected at the front of the vehicle the HC sensor resistance and signal voltage are low. When high levels of NOX are detected at the front of the vehicle the Nox sensor resistance and signal voltage are high.

Reference Information

Schematic Reference

HVAC Schematics

Connector End View Reference

Component Connector End Views

Description and Operation

Automatic HVAC Description and Operation

Electrical Information Reference

1. «Circuit Testing»(/cadillac/sts/i-2007-2011/remont/body-electrical/#wiring-systems-and-power-management-service-troubleshooting-diagnosis__circuit-testing)
2. «Connector Repairs»(/cadillac/sts/i-2007-2011/remont/body-electrical/#wiring-systems-and-power-management-service-troubleshooting-diagnosis__connector-repairs)
3. «Testing for Intermittent Conditions and Poor Connections»(/cadillac/sts/i-2007-2011/remont/body-electrical/#wiring-systems-and-power-management-service-troubleshooting-diagnosis__testing-for-intermittent-conditions-and-poor)
4. «Wiring Repairs»(/cadillac/sts/i-2007-2011/remont/body-electrical/#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 air quality sensor.
2. Test for less than 5 ohms between the ground circuit terminal 6 and ground. If greater than the specified range, test the ground circuit for an open/high resistance.
3. Ignition OFF, test for less than 5 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 test normal test or replace the HVAC control module.
4. Ignition ON, verify that a test lamp illuminates between the B+ circuit terminal 3 and ground. If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance.
5. Test for 4.8-5.2 volts between the ground circuit terminal 6 and the signal circuit terminal 4. If less than the specified range, test the signal circuit for a open/high resistance. If the circuit tests normal, replace the HVAC control module.
6. Test for 4.8-5.2 volts between the ground circuit terminal 6 and the signal circuit terminal 2. If less than the specified range, test the signal circuit for a open/high resistance. If the circuit tests normal, replace the HVAC control module.
7. If all circuits test normal, test or replace the air quality sensor.

Repair Procedures

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

1. «Outside Air Quality Sensor Replacement»(/cadillac/sts/i-2007-2011/remont/automatic-hvac-system/#hvac-system-automatic)
2. «Control Module References»(/cadillac/sts/i-2007-2011/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/sts/i-2007-2011/remont/oem-general-information/#vehicle-diagnostic-information-2-of-2) prior to using this diagnostic procedure.
2. Review «Strategy Based Diagnosis»(/cadillac/sts/i-2007-2011/remont/oem-general-information/#vehicle-diagnostic-information-2-of-2__strategy-based-diagnosis) for an overview of the diagnostic approach.
3. «Diagnostic Procedure Instructions»(/cadillac/sts/i-2007-2011/remont/oem-general-information/#vehicle-diagnostic-information-2-of-2__diagnostic-procedure-instructions) provides an overview of each diagnostic category.

Circuit/System Description

The HVAC control module monitors the air temperature sensors with a low reference circuit and 5-volt signal circuit. The HVAC control module monitors the voltage drop across the sensor, which is proportional to temperature. When the ambient air temperatures are cold, the resistance of the sensor is high and the voltage signals are high. When the ambient air temperatures are hot, the resistance of the sensors is low and the voltage signals are low.

Conditions for Running the DTC

Ignition ON.

Conditions for Setting the DTC

1. The HVAC control module detects the sensor signal circuit is less than -35°C (-39°F).
2. The HVAC control module detects the sensor signal circuit is greater than 85°C (185°F).

Action Taken When the DTC Sets

1. The HVAC control module uses a default air temperature value for further automatic control calculations. The default values are not displayed on the scan tool.
2. SERVICE A/C SYSTEM will be displayed on the DIC.

Conditions for Clearing the DTC

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

Schematic Reference

HVAC Schematics

Connector End View Reference

Component Connector End Views

Description and Operation

Automatic HVAC Description and Operation

Electrical Information Reference

1. «Circuit Testing»(/cadillac/sts/i-2007-2011/remont/body-electrical/#wiring-systems-and-power-management-service-troubleshooting-diagnosis__circuit-testing)
2. «Connector Repairs»(/cadillac/sts/i-2007-2011/remont/body-electrical/#wiring-systems-and-power-management-service-troubleshooting-diagnosis__connector-repairs)
3. «Testing for Intermittent Conditions and Poor Connections»(/cadillac/sts/i-2007-2011/remont/body-electrical/#wiring-systems-and-power-management-service-troubleshooting-diagnosis__testing-for-intermittent-conditions-and-poor)
4. «Wiring Repairs»(/cadillac/sts/i-2007-2011/remont/body-electrical/#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 appropriate air temperature sensor. The reading should be between -35°C (-39°F) and 85°C (185°F) and change with air temperature changes.

1. Ignition OFF, disconnect the harness connector at the appropriate air temperature sensor.
2. Ignition OFF, test for less than 10 ohms between the low reference circuit terminal listed below and ground: Ambient air temperature sensor terminal B Inside air temperature sensor terminal 1 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 scan tool appropriate Air Temp Sensor parameter is less than -35°C (-39°F). If greater than the specified range, test the signal circuit terminal listed below for a short to ground. If the circuit tests normal, replace the HVAC control module. Ambient air temperature sensor terminal A Inside air temperature sensor terminal 2
4. Install a 3A fused jumper wire between the signal circuit terminal listed below and the low reference circuit terminal listed below. Verify the scan tool Air Temp Sensor parameter is greater than 85°C (185°F). Ambient air temperature sensor signal circuit terminal A and low reference circuit terminal B Inside air temperature sensor signal circuit terminal 2 and low reference circuit terminal 1 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.
5. If all circuits test normal, test or replace the appropriate air temperature sensor.

Component Testing

1. Test the appropriate air temperature sensor by varying the sensor temperature while monitoring the sensor resistance.
2. Compare the readings with the Temperature VS Resistance table «Sensor Resistance Table»(/cadillac/sts/i-2007-2011/remont/automatic-hvac-system/#hvac-system-automatic__sensor-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/sts/i-2007-2011/remont/automatic-hvac-system/#hvac-system-automatic)
2. «Inside Air Temperature Sensor Replacement»(/cadillac/sts/i-2007-2011/remont/automatic-hvac-system/#hvac-system-automatic)
3. «Control Module References»(/cadillac/sts/i-2007-2011/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/sts/i-2007-2011/remont/oem-general-information/#vehicle-diagnostic-information-2-of-2) prior to using this diagnostic procedure.
2. Review «Strategy Based Diagnosis»(/cadillac/sts/i-2007-2011/remont/oem-general-information/#vehicle-diagnostic-information-2-of-2__strategy-based-diagnosis) for an overview of the diagnostic approach.
3. «Diagnostic Procedure Instructions»(/cadillac/sts/i-2007-2011/remont/oem-general-information/#vehicle-diagnostic-information-2-of-2__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 two sensors are integrated into the sunload sensor assembly along with the ambient light sensor. Ground and signal circuits enable the sensors to operate. As the sunload increases, the sensor signal decreases. The sensor signal varies between 0 and 5 volts. The HVAC control module converts the signal to a range between 0 and 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.

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

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

Ignition ON.

The HVAC control module detects the signal circuit is less than 5 counts or greater than 250 counts.

1. The driver information center (DIC) will display SERVICE A/C SYSTEM.
2. The system will operate 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 50 fault-free ignition cycles.

Schematic Reference

HVAC Schematics

Connector End View Reference

Component Connector End Views

Description and Operation

Automatic HVAC Description and Operation

Electrical Information Reference

1. «Circuit Testing»(/cadillac/sts/i-2007-2011/remont/body-electrical/#wiring-systems-and-power-management-service-troubleshooting-diagnosis__circuit-testing)
2. «Connector Repairs»(/cadillac/sts/i-2007-2011/remont/body-electrical/#wiring-systems-and-power-management-service-troubleshooting-diagnosis__connector-repairs)
3. «Testing for Intermittent Conditions and Poor Connections»(/cadillac/sts/i-2007-2011/remont/body-electrical/#wiring-systems-and-power-management-service-troubleshooting-diagnosis__testing-for-intermittent-conditions-and-poor)
4. «Wiring Repairs»(/cadillac/sts/i-2007-2011/remont/body-electrical/#wiring-systems-and-power-management-service-troubleshooting-diagnosis__wiring-repairs)

Scan Tool Reference

Control Module References for scan tool information

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

1. Ignition OFF, disconnect the harness connector at the sunload sensor.
2. 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 an open/high resistance.
3. Ignition ON, test for 4.8-5.2 volts between the ground circuit terminal C and the appropriate signal circuit terminal listed below: Left solar load sensor circuit terminal A. Right solar load sensor circuit terminal B. If less than the specified range, test the signal circuit for a short to ground or open/high resistance. If the circuit tests normal, replace the HVAC control module. 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.
4. If all circuits test normal, test or replace the sunload sensor.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

1. «Sun Load Temperature Sensor Replacement»(/cadillac/sts/i-2007-2011/remont/automatic-hvac-system/#hvac-system-automatic)
2. «Control Module References»(/cadillac/sts/i-2007-2011/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/sts/i-2007-2011/remont/oem-general-information/#vehicle-diagnostic-information-2-of-2) prior to using this diagnostic procedure.
2. Review «Strategy Based Diagnosis»(/cadillac/sts/i-2007-2011/remont/oem-general-information/#vehicle-diagnostic-information-2-of-2__strategy-based-diagnosis) for an overview of the diagnostic approach.
3. «Diagnostic Procedure Instructions»(/cadillac/sts/i-2007-2011/remont/oem-general-information/#vehicle-diagnostic-information-2-of-2__diagnostic-procedure-instructions) provides an overview of the diagnostic category.

The actuators operate using 5 circuits. A 5-volt reference, low reference, signal circuit and two bi-directional 0 or 12 volt control circuits. The HVAC control module supplies a low reference and 5-volt reference to the potentiometer. The HVAC control module monitors the voltage drop across the potentiometer on the door position signal circuit. As the actuator door changes position the door position signal circuit voltage also changes. The two bi-directional control circuits enable the actuator to operate. Both circuits are set to 0 volts when the HVAC control module detects, from the feedback potentiometer, that the actuator is in the desired position. In order to move the actuator, the HVAC control module switches the appropriate control circuit to 12 volts.

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 more than 4 counts or the HVAC control module detects the door position signal circuit is less than 7 counts or greater than 250 counts.

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 50 fault-free ignition cycles.

Schematic Reference

HVAC Schematics

Connector End View Reference

Component Connector End Views

Description and Operation

Automatic HVAC Description and Operation

Electrical Information Reference

1. «Circuit Testing»(/cadillac/sts/i-2007-2011/remont/body-electrical/#wiring-systems-and-power-management-service-troubleshooting-diagnosis__circuit-testing)
2. «Connector Repairs»(/cadillac/sts/i-2007-2011/remont/body-electrical/#wiring-systems-and-power-management-service-troubleshooting-diagnosis__connector-repairs)
3. «Testing for Intermittent Conditions and Poor Connections»(/cadillac/sts/i-2007-2011/remont/body-electrical/#wiring-systems-and-power-management-service-troubleshooting-diagnosis__testing-for-intermittent-conditions-and-poor)
4. «Wiring Repairs»(/cadillac/sts/i-2007-2011/remont/body-electrical/#wiring-systems-and-power-management-service-troubleshooting-diagnosis__wiring-repairs)

Scan Tool Reference

Control Module References for scan tool information

Ignition ON, command the appropriate actuator to 100 percent with a scan tool. The scan tool should display between 224 and 230 counts on the mode actuator, all other actuators should display between 199 and 205 counts.

1. Disconnect the harness connector at the appropriate actuator.
2. Ignition OFF, test for less than 1 ohm between the low reference circuit terminal 1 and ground. If greater than the specified range, test the low reference circuit for a short to voltage or 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 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 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 4 counts. If greater than the specified range, test the signal circuit terminal 3 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 1. Verify the appropriate scan tool parameter is greater than 250 counts. If less than the specified range, test the signal circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the HVAC control module.
6. Ignition ON, after 30 seconds verify that a test lamp illuminates between control circuit A terminal 5 and B+. If the test lamp does not illuminate, test the control circuit for a short to voltage or an open/high resistance. If circuit tests normal replace the HVAC control module.
7. Ignition OFF, verify that the test lamp does not illuminate between control circuit A terminal 5 and B+. If the test lamp illuminate, test the control circuit for a short to ground. If circuit tests normal replace the HVAC control module.
8. Ignition ON, after 30 seconds verify that a test lamp illuminates between control circuit B terminal 4 and B+. If the test lamp does not illuminate, test the control circuit for a short to voltage or an open/high resistance. If circuit tests normal replace the HVAC control module.
9. Ignition OFF, verify that the test lamp does not illuminate between control circuit B terminal 4 and B+. If the test lamp illuminate, test the control circuit for a short to ground. If circuit tests normal replace the HVAC control module.
10. If all circuits test normal, test or replace the actuator.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

1. «Recirculation Actuator Replacement»(/cadillac/sts/i-2007-2011/remont/automatic-hvac-system/#hvac-system-automatic)
2. «Mode Actuator Replacement»(/cadillac/sts/i-2007-2011/remont/automatic-hvac-system/#hvac-system-automatic)
3. «Temperature Valve Actuator Replacement - Left Side»(/cadillac/sts/i-2007-2011/remont/automatic-hvac-system/#hvac-system-automatic)
4. «Temperature Valve Actuator Replacement - Right Side»(/cadillac/sts/i-2007-2011/remont/automatic-hvac-system/#hvac-system-automatic)
5. «Auxiliary Temperature Valve Actuator Replacement»(/cadillac/sts/i-2007-2011/remont/automatic-hvac-system/#hvac-system-automatic)
6. «Mode Actuator Replacement - Console»(/cadillac/sts/i-2007-2011/remont/automatic-hvac-system/#hvac-system-automatic)
7. «Control Module References»(/cadillac/sts/i-2007-2011/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/sts/i-2007-2011/remont/oem-general-information/#vehicle-diagnostic-information-2-of-2) prior to using this diagnostic procedure.
2. Review «Strategy Based Diagnosis»(/cadillac/sts/i-2007-2011/remont/oem-general-information/#vehicle-diagnostic-information-2-of-2__strategy-based-diagnosis) for an overview of the diagnostic approach.
3. «Diagnostic Procedure Instructions»(/cadillac/sts/i-2007-2011/remont/oem-general-information/#vehicle-diagnostic-information-2-of-2__diagnostic-procedure-instructions) provides an overview of each diagnostic category.

The HVAC control module monitors the outside air quality via the air quality sensor assembly while in AUTO mode. The air quality sensor is a 5-wire sensor with a single ignition voltage circuit, a ground circuit, a low reference circuit, and two signal circuits. There are 2 sensors inside the air quality sensor assembly. A hydrocarbon (HC) sensor which is used for detecting gasoline exhaust fumes and a NOX sensor which is used for detecting oxides of nitrogen. When high levels of HC are detected at the front of the vehicle the HC sensor resistance and signal voltage are low. When high levels of NOX are detected at the front of the vehicle the Nox sensor resistance and signal voltage are high.

1. Ignition ON
2. DTC B1325 is not set

The HVAC control module detects the air quality sensor signal that is less than 0.09 volt for more than 30 seconds

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

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

Schematic Reference

HVAC Schematics

Connector End View Reference

Component Connector End Views

Description and Operation

Automatic HVAC Description and Operation

Electrical Information Reference

1. «Circuit Testing»(/cadillac/sts/i-2007-2011/remont/body-electrical/#wiring-systems-and-power-management-service-troubleshooting-diagnosis__circuit-testing)
2. «Connector Repairs»(/cadillac/sts/i-2007-2011/remont/body-electrical/#wiring-systems-and-power-management-service-troubleshooting-diagnosis__connector-repairs)
3. «Testing for Intermittent Conditions and Poor Connections»(/cadillac/sts/i-2007-2011/remont/body-electrical/#wiring-systems-and-power-management-service-troubleshooting-diagnosis__testing-for-intermittent-conditions-and-poor)
4. «Wiring Repairs»(/cadillac/sts/i-2007-2011/remont/body-electrical/#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 air quality sensor.
2. Test for less than 5 ohms between the ground circuit terminal 6 and ground. If greater than the specified range, test the ground circuit for an open/high resistance.
3. Test for less than 5 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 test normal test or replace the HVAC control module.
4. Ignition ON, verify that a test lamp illuminates between the B+ circuit terminal 3 and ground. If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance.
5. Test for 4.8-5.2 volts between the ground circuit terminal 6 and the signal circuit terminal 4. If less than the specified range, test the signal circuit for a open/high resistance. If the circuit tests normal, replace the HVAC control module.
6. Test for 4.8-5.2 volts between the ground circuit terminal 6 and the signal circuit terminal 2. If less than the specified range, test the signal circuit for a open/high resistance. If the circuit tests normal, replace the HVAC control module.
7. If all circuits test normal, test or replace the air quality sensor.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

1. «Outside Air Quality Sensor Replacement»(/cadillac/sts/i-2007-2011/remont/automatic-hvac-system/#hvac-system-automatic)
2. «Control Module References»(/cadillac/sts/i-2007-2011/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/sts/i-2007-2011/remont/oem-general-information/#vehicle-diagnostic-information-2-of-2) prior to using this diagnostic procedure.
2. Review «Strategy Based Diagnosis»(/cadillac/sts/i-2007-2011/remont/oem-general-information/#vehicle-diagnostic-information-2-of-2__strategy-based-diagnosis) for an overview of the diagnostic approach.
3. «Diagnostic Procedure Instructions»(/cadillac/sts/i-2007-2011/remont/oem-general-information/#vehicle-diagnostic-information-2-of-2__diagnostic-procedure-instructions) provides an overview of each diagnostic category.

The HVAC control module supplies the evaporator 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 and the voltage signal decreases. As the air temperature decreases, the sensor resistance increases and the voltage signal increases.

Ignition ON.

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

1. The driver information center (DIC) will display SERVICE A/C SYSTEM.
2. The air conditioning (A/C) compressor will be disabled.

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

Schematic Reference

HVAC Schematics

Connector End View Reference

Component Connector End Views

Description and Operation

Automatic HVAC Description and Operation

Electrical Information Reference

1. «Circuit Testing»(/cadillac/sts/i-2007-2011/remont/body-electrical/#wiring-systems-and-power-management-service-troubleshooting-diagnosis__circuit-testing)
2. «Connector Repairs»(/cadillac/sts/i-2007-2011/remont/body-electrical/#wiring-systems-and-power-management-service-troubleshooting-diagnosis__connector-repairs)
3. «Testing for Intermittent Conditions and Poor Connections»(/cadillac/sts/i-2007-2011/remont/body-electrical/#wiring-systems-and-power-management-service-troubleshooting-diagnosis__testing-for-intermittent-conditions-and-poor)
4. «Wiring Repairs»(/cadillac/sts/i-2007-2011/remont/body-electrical/#wiring-systems-and-power-management-service-troubleshooting-diagnosis__wiring-repairs)

Scan Tool Reference

Control Module References for scan tool information

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

1. Ignition OFF, disconnect the harness connector at the evaporator temperature sensor.
2. Ignition OFF, test for less than 10 ohms 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 low reference circuit terminal 2 and the signal circuit terminal 1. If less than the specified voltage, test the signal circuit for a short to ground or open/high resistance. If the circuit tests normal, replace the HVAC control module. If greater than the specified voltage, test the signal circuit for a short to voltage. If the circuit tests normal, replace the HVAC control module.
4. If all circuits test normal, test or replace the evaporator air temperature sensor.

1. Test the evaporator air temperature sensor by varying the sensor temperature while monitoring the sensor resistance.
2. Compare the readings with the Temperature VS Resistance table «Sensor Resistance Table»(/cadillac/sts/i-2007-2011/remont/automatic-hvac-system/#hvac-system-automatic__sensor-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.

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

1. Perform the «Diagnostic System Check - Vehicle»(/cadillac/sts/i-2007-2011/remont/oem-general-information/#vehicle-diagnostic-information-2-of-2) prior to using this diagnostic procedure.
2. Review «Strategy Based Diagnosis»(/cadillac/sts/i-2007-2011/remont/oem-general-information/#vehicle-diagnostic-information-2-of-2__strategy-based-diagnosis) for an overview of the diagnostic approach.
3. «Diagnostic Procedure Instructions»(/cadillac/sts/i-2007-2011/remont/oem-general-information/#vehicle-diagnostic-information-2-of-2__diagnostic-procedure-instructions) provides an overview of the 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 sensor signal to the ECM to vary. When the pressure is high, the signal voltage is high. When the pressure is low, the signal voltage is low. When pressure is high, the ECM commands the cooling fans on. When pressure is too high or too low, the ECM will not allow the A/C compressor clutch to engage.

1. Engine is running.
2. Any of the conditions for setting the DTC are met for 15 seconds.
3. Battery voltage is between 11-18 volts.

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 more than 428 psi (4.92 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.

Diagnostic Aids

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

Automatic HVAC Description and Operation

Electrical Information Reference

1. «Circuit Testing»(/cadillac/sts/i-2007-2011/remont/body-electrical/#wiring-systems-and-power-management-service-troubleshooting-diagnosis__circuit-testing)
2. «Connector Repairs»(/cadillac/sts/i-2007-2011/remont/body-electrical/#wiring-systems-and-power-management-service-troubleshooting-diagnosis__connector-repairs)
3. «Testing for Intermittent Conditions and Poor Connections»(/cadillac/sts/i-2007-2011/remont/body-electrical/#wiring-systems-and-power-management-service-troubleshooting-diagnosis__testing-for-intermittent-conditions-and-poor)
4. «Wiring Repairs»(/cadillac/sts/i-2007-2011/remont/body-electrical/#wiring-systems-and-power-management-service-troubleshooting-diagnosis__wiring-repairs)

Scan Tool Reference

Control Module References for scan tool information

Ignition ON, observe the scan tool A/C High Side Pressure Sensor parameter. The reading should be between 1 psi and 428 psi.

1. Ignition OFF, disconnect the A/C pressure sensor harness connector.
2. Ignition OFF, test for less than 1 ohm 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 428 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 428 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 pressure sensor.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

1. «Air Conditioning (A/C) Refrigerant Pressure Sensor Replacement»(/cadillac/sts/i-2007-2011/remont/automatic-hvac-system/#heating-ventilation-and-air-conditioning)
2. «Control Module References»(/cadillac/sts/i-2007-2011/remont/communication-devices/#programming-and-setup-all-systems__control-module-references) for ECM replacement, setup, and programming

1. Perform the «Diagnostic System Check - Vehicle»(/cadillac/sts/i-2007-2011/remont/oem-general-information/#vehicle-diagnostic-information-2-of-2) prior to using this diagnostic procedure.
2. Review «Strategy Based Diagnosis»(/cadillac/sts/i-2007-2011/remont/oem-general-information/#vehicle-diagnostic-information-2-of-2__strategy-based-diagnosis) for an overview of the diagnostic approach.
3. «Diagnostic Procedure Instructions»(/cadillac/sts/i-2007-2011/remont/oem-general-information/#vehicle-diagnostic-information-2-of-2__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 9 and 18 volts.
2. The engine speed is more than 80 RPM.
3. The ECM A/C Compressor Clutch Relay Control transitions between 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.

1. The A/C clutch relay is commanded OFF.
2. The conditions for which the DTC was set will be stored in the Failure Records data only. No information will be stored as Freeze Frame data.

The history DTC will clear after 40 fault-free ignition cycles.

Schematic Reference

HVAC Schematics

Connector End View Reference

Component Connector End Views

Description and Operation

Automatic HVAC Description and Operation

Electrical Information Reference

1. «Circuit Testing»(/cadillac/sts/i-2007-2011/remont/body-electrical/#wiring-systems-and-power-management-service-troubleshooting-diagnosis__circuit-testing)
2. «Connector Repairs»(/cadillac/sts/i-2007-2011/remont/body-electrical/#wiring-systems-and-power-management-service-troubleshooting-diagnosis__connector-repairs)
3. «Testing for Intermittent Conditions and Poor Connections»(/cadillac/sts/i-2007-2011/remont/body-electrical/#wiring-systems-and-power-management-service-troubleshooting-diagnosis__testing-for-intermittent-conditions-and-poor)
4. «Wiring Repairs»(/cadillac/sts/i-2007-2011/remont/body-electrical/#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 COMP relay.
2. Ignition ON, verify that a test lamp does not illuminate between the control circuit terminal 85 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 86 and ground. If the test lamp does not illuminate, test the ignition circuit for a short to ground or an open/high resistance. If the circuit tests normal and ignition circuit fuse is open, test or replace the relay.
4. Connect a test lamp between the ignition circuit terminal 86 and the control circuit terminal 85.
5. Command the A/C relay 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.
6. If all circuits test normal, test or replace the A/C COMP relay.

1. Ignition OFF, disconnect the A/C COMP relay.
2. Test for 60-180 ohms between terminals 85 and 86. If the resistance is not within the specified range, replace the relay.
3. Test for infinite resistance between the following terminals: 30 and 86 30 and 87 30 and 85 85 and 87 If not the specified value, replace the relay.
4. Install a 30A fused jumper wire between relay terminal 85 and 12 volts. Install a jumper wire between relay terminal 86 and ground. Test for less than 2 ohms between terminals 30 and 87. If greater than the specified range, replace the relay.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

Control Module References for ECM setup, replacement, and programming

Symptoms - HVAC Systems - Automatic

1. Perform the «Diagnostic System Check - Vehicle»(/cadillac/sts/i-2007-2011/remont/oem-general-information/#vehicle-diagnostic-information-2-of-2) before using the Symptom Tables in order to verify that all of the following are true: There are no DTCs set. The control modules can communicate via the serial data link.
2. Review the system operation in order to familiarize yourself with the system functions. Refer to «Automatic HVAC Description and Operation»(/cadillac/sts/i-2007-2011/remont/automatic-hvac-system/#hvac-system-automatic)

Visual/Physical Inspection

1. Inspect for aftermarket devices which could affect the operation of the HVAC System. Refer to «Checking Aftermarket Accessories»(/cadillac/sts/i-2007-2011/remont/body-electrical/#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. Verify that the customer is using the correct key to enable personalization and is not inadvertently activating auxiliary HVAC controls.
5. The A/C compressor will not operate in cold outside air temperatures.
6. The following conditions may cause window fogging: Wet carpet or mats High humidity Interior water leak Blocked A/C evaporator drain tube Maximum passenger capacity Blocked body pressure relief valves
7. Inspect the air distribution system for causes of reduced air flow: Obstructed or dirty passenger compartment air filter, if equipped Blocked or damaged air inlet or outlet vents

Intermittent

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

Symptom List

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

1. «Air Conditioning Compressor Malfunction»(/cadillac/sts/i-2007-2011/remont/automatic-hvac-system/#hvac-system-automatic)
2. «Blower Motor Malfunction»(/cadillac/sts/i-2007-2011/remont/automatic-hvac-system/#hvac-system-automatic)
3. «Air Temperature Malfunction»(/cadillac/sts/i-2007-2011/remont/automatic-hvac-system/#hvac-system-automatic)

1. Perform the «Diagnostic System Check - Vehicle»(/cadillac/sts/i-2007-2011/remont/oem-general-information/#vehicle-diagnostic-information-2-of-2) prior to using this diagnostic procedure.
2. Review «Strategy Based Diagnosis»(/cadillac/sts/i-2007-2011/remont/oem-general-information/#vehicle-diagnostic-information-2-of-2__strategy-based-diagnosis) for an overview of the diagnostic approach.
3. «Diagnostic Procedure Instructions»(/cadillac/sts/i-2007-2011/remont/oem-general-information/#vehicle-diagnostic-information-2-of-2__diagnostic-procedure-instructions) provides an overview of each diagnostic category.

When the A/C switch is pressed, the HVAC control assembly sends a GMLAN 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 CMPR 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 greater than 600 RPM.
4. Engine speed is less than 4,760 RPM.
5. A/C high side pressure is between 2929-269 kPa (39-425 psi) «Air Conditioning (A/C) System Performance Test (LY7 w/ Heavy Duty Cooling)»(/cadillac/sts/i-2007-2011/remont/automatic-hvac-system/#heating-ventilation-and-air-conditioning) or «Air Conditioning (A/C) System Performance Test (LY7 w/Standard Cooling)»(/cadillac/sts/i-2007-2011/remont/automatic-hvac-system/#heating-ventilation-and-air-conditioning) or «Air Conditioning (A/C) System Performance Test (LC3)»(/cadillac/sts/i-2007-2011/remont/automatic-hvac-system/#heating-ventilation-and-air-conditioning) or «Air Conditioning (A/C) System Performance Test (LH2 w/ Heavy Duty Cooling)»(/cadillac/sts/i-2007-2011/remont/automatic-hvac-system/#heating-ventilation-and-air-conditioning) or «Air Conditioning (A/C) System Performance Test (LH2 w/ Standard Cooling)»(/cadillac/sts/i-2007-2011/remont/automatic-hvac-system/#heating-ventilation-and-air-conditioning) .
6. Throttle position is less than 100 percent.
7. Evaporator temperature is greater than 0°C (32°F).
8. ECM does not detect excessive torque load.
9. ECM does not detect insufficient idle quality.
10. The ambient temperature is above 1°C (34°F).

Schematic Reference

HVAC Schematics

Connector End View Reference

Component Connector End Views

Description and Operation

Automatic HVAC Description and Operation

Electrical Information Reference

1. «Circuit Testing»(/cadillac/sts/i-2007-2011/remont/body-electrical/#wiring-systems-and-power-management-service-troubleshooting-diagnosis__circuit-testing)
2. «Connector Repairs»(/cadillac/sts/i-2007-2011/remont/body-electrical/#wiring-systems-and-power-management-service-troubleshooting-diagnosis__connector-repairs)
3. «Testing for Intermittent Conditions and Poor Connections»(/cadillac/sts/i-2007-2011/remont/body-electrical/#wiring-systems-and-power-management-service-troubleshooting-diagnosis__testing-for-intermittent-conditions-and-poor)
4. «Wiring Repairs»(/cadillac/sts/i-2007-2011/remont/body-electrical/#wiring-systems-and-power-management-service-troubleshooting-diagnosis__wiring-repairs)

Scan Tool Reference

Control Module References for scan tool information

Engine running, press the A/C request switch. The A/C compressor clutch should engage.

1. Ignition ON, with a scan tool, verify the A/C Switch parameter cycles between On and Off with each press of the A/C switch If the parameter does not cycle, replace the HVAC control module.
2. Remove the A/C CLTCH relay.
3. Verify that a test lamp illuminates between the B+ circuit terminal 85 and ground. If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance.
4. Verify that a test lamp illuminates between the B+ circuit terminal 30 and ground. If the test lamp does not illuminate, test the relay switch B+ circuit for an open/high resistance. If the A/C clutch fuse is open, test the relay switch control circuit for a short to ground. If all circuits test normal, test or replace the A/C compressor clutch.
5. Disconnect the harness connector at the A/C compressor clutch.
6. Ignition OFF test for less than 1.0 ohm between the A/C compressor 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 compressor clutch.
8. Connect a 10A fused jumper wire between the B+ circuit terminal 30 and the relay switch control circuit terminal 87. Verify the A/C compressor clutch engages. If the A/C compressor clutch does not activate, test the control circuit for an open/high resistance. If the circuit tests normal, test or replace the A/C compressor.
9. Connect a test lamp between the relay control circuit terminal 86 and the B+ circuit terminal 85.
10. Using a scan tool, command the A/C relay output ON and OFF. The test lamp should turn ON and OFF when changing between the commanded states. If the test lamp remains ON all the time, test for a short to ground on the control circuit connector X1 terminal 53. If the circuit tests normal, replace the ECM. If the test lamp remains OFF all the time, test for a short to voltage or an open/high resistance on the control circuit. If the circuit tests normal, replace the ECM.
11. If all circuits test normal, test or replace the A/C compressor.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

1. «Air Conditioning Compressor Replacement (LY7)»(/cadillac/sts/i-2007-2011/remont/automatic-hvac-system/#heating-ventilation-and-air-conditioning) or «Air Conditioning Compressor Replacement (LH2)»(/cadillac/sts/i-2007-2011/remont/automatic-hvac-system/#heating-ventilation-and-air-conditioning)
2. «Compressor Relay Replacement»(/cadillac/sts/i-2007-2011/remont/automatic-hvac-system/#heating-ventilation-and-air-conditioning)
3. «Control Module References»(/cadillac/sts/i-2007-2011/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/sts/i-2007-2011/remont/oem-general-information/#vehicle-diagnostic-information-2-of-2) prior to using this diagnostic procedure.
2. Review «Strategy Based Diagnosis»(/cadillac/sts/i-2007-2011/remont/oem-general-information/#vehicle-diagnostic-information-2-of-2__strategy-based-diagnosis) for an overview of the diagnostic approach.
3. «Diagnostic Procedure Instructions»(/cadillac/sts/i-2007-2011/remont/oem-general-information/#vehicle-diagnostic-information-2-of-2__diagnostic-procedure-instructions) provides an overview of each diagnostic category.

Blower Controller

The blower 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 controller in order to command the blower motor speed. The control processor uses the blower motor ground or low reference 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 6 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.

Schematic Reference

HVAC Schematics

Connector End View Reference

Component Connector End Views

Description and Operation

Automatic HVAC Description and Operation

Electrical Information Reference

1. «Circuit Testing»(/cadillac/sts/i-2007-2011/remont/body-electrical/#wiring-systems-and-power-management-service-troubleshooting-diagnosis__circuit-testing)
2. «Connector Repairs»(/cadillac/sts/i-2007-2011/remont/body-electrical/#wiring-systems-and-power-management-service-troubleshooting-diagnosis__connector-repairs)
3. «Testing for Intermittent Conditions and Poor Connections»(/cadillac/sts/i-2007-2011/remont/body-electrical/#wiring-systems-and-power-management-service-troubleshooting-diagnosis__testing-for-intermittent-conditions-and-poor)
4. «Wiring Repairs»(/cadillac/sts/i-2007-2011/remont/body-electrical/#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. Press the fan speed control button from the lowest to highest setting. The blower motor speed should change between commanded states.
2. Press the power button located on the drivers side of the climate control panel to turn the entire climate control system ON or OFF. The blower motor should turn OFF.

1. Ignition OFF, disconnect the BLOWER 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 B+ circuit terminal 87 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 BLOWER fuse is open, test the B+ circuit for a short to ground. If the circuit tests normal, replace the blower controller.
4. Connect a test lamp between the control circuit terminal 86 and B+.
5. Command the blower motor ON and OFF. The test lamp should turn ON and OFF when changing between the commanded states. 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 HVAC control module. If test lamp is always ON, test for short to ground. If circuit tests normal, replace the blower relay.
6. Connect the BLOWER relay.
7. Ignition OFF, disconnect the X2 harness connector at the blower controller.
8. Test for less than 1 ohm between the ground circuit terminal 5 and ground. If not the specified range, test the ground circuit for an open/high resistance.
9. Connect a test lamp between the B+ circuit terminal 6 and ground.
10. Turn ON the blower motor. Verify the test lamp illuminates. If the test lamp does not illuminate, test the B+ circuit for an open/high resistance. If the circuit tests normal, test or replace the BLOWER relay.
11. Install a test lamp between the control circuit terminal 3 and B+.
12. Turn the blower motor ON and cycle between low and high speeds. The test lamp should dimly illuminate at high speeds and reduce in intensity as the blower speed is reduced. If the test lamp does not illuminate, test the control circuit for short to voltage or an open/high resistance. If the circuits test normal, test or replace the HVAC control module. If the test lamp does not change intensity, test the control circuit for a short to ground. If the circuit tests normal, test or replace the HVAC control module.
13. Connect the harness connector at the blower controller.
14. Disconnect the harness connector at the blower motor.
15. Install at test lamp between the B+ circuit terminal 2 and ground.
16. Turn ON the blower motor. Verify the test lamp illuminates. If the test lamp does not illuminate, test the B+ circuit for an open/high resistance.
17. Install a test lamp between the control circuit terminal 1 and the B+ circuit terminal 2.
18. Turn the blower motor ON and cycle between low and high speeds. The test lamp should illuminate and change in intensity as the blower speed is varied. If the test lamp does not illuminate, test the low reference circuit for short to voltage or an open/high resistance. If the circuit tests normal, test or replace the blower controller. If the test lamp does not change intensity, test the low reference circuit for a short to ground. If the circuit tests normal, test or replace the blower controller.
19. If all circuits test normal, test or replace the blower motor.

Blower Relay

1. Ignition OFF, disconnect the BLOWER relay.
2. Test for 60-180 ohms between terminals 85 and 86. If the resistance is not within the specified range, replace the relay.
3. Test for infinite resistance between the following terminals: 30 and 86 30 and 87 30 and 85 85 and 87 If not the specified value, replace the relay.
4. Test for less than 2 ohms between terminals 30 and 87A. If greater than the specified range, replace the relay.
5. Install a 40A fused jumper wire between relay terminal 85 and 12 volts. Install a jumper wire between relay terminal 86 and ground. Test for less than 2 ohms between terminals 30 and 87. If greater than the specified range, replace the relay.

Blower Motor

1. Ignition OFF, disconnect the harness at the blower motor.
2. Install a 40A 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/sts/i-2007-2011/remont/automatic-hvac-system/#heating-ventilation-and-air-conditioning)
2. «Control Module References»(/cadillac/sts/i-2007-2011/remont/communication-devices/#programming-and-setup-all-systems__control-module-references) for blower controller and HVAC control module replacement, setup, and programming

1. Perform the «Diagnostic System Check - Vehicle»(/cadillac/sts/i-2007-2011/remont/oem-general-information/#vehicle-diagnostic-information-2-of-2) prior to using this diagnostic procedure.
2. Review «Strategy Based Diagnosis»(/cadillac/sts/i-2007-2011/remont/oem-general-information/#vehicle-diagnostic-information-2-of-2__strategy-based-diagnosis) for an overview of the diagnostic approach.
3. «Diagnostic Procedure Instructions»(/cadillac/sts/i-2007-2011/remont/oem-general-information/#vehicle-diagnostic-information-2-of-2__diagnostic-procedure-instructions) provides an overview of each diagnostic category.

Evaporator, Inside and 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, which is proportional to temperature. 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 vehicles 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

Automatic HVAC Description and Operation

Electrical Information Reference

1. «Circuit Testing»(/cadillac/sts/i-2007-2011/remont/body-electrical/#wiring-systems-and-power-management-service-troubleshooting-diagnosis__circuit-testing)
2. «Connector Repairs»(/cadillac/sts/i-2007-2011/remont/body-electrical/#wiring-systems-and-power-management-service-troubleshooting-diagnosis__connector-repairs)
3. «Testing for Intermittent Conditions and Poor Connections»(/cadillac/sts/i-2007-2011/remont/body-electrical/#wiring-systems-and-power-management-service-troubleshooting-diagnosis__testing-for-intermittent-conditions-and-poor)
4. «Wiring Repairs»(/cadillac/sts/i-2007-2011/remont/body-electrical/#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 «Circuit/System Testing»(/cadillac/sts/i-2007-2011/remont/automatic-hvac-system/#hvac-system-automatic) , under Sunload Sensor Circuit Malfunction.
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 the parameter. If not within the specified range, refer to «Circuit/System Testing»(/cadillac/sts/i-2007-2011/remont/automatic-hvac-system/#hvac-system-automatic) , under Evaporator and Ambient Air Temperature Sensor Circuit Malfunction.
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 the parameter. If not within the specified range, «Circuit/System Testing»(/cadillac/sts/i-2007-2011/remont/automatic-hvac-system/#hvac-system-automatic) , under Inside Air Temperature Sensor Circuit Malfunction.
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 «Circuit/System Testing»(/cadillac/sts/i-2007-2011/remont/automatic-hvac-system/#hvac-system-automatic) , under Evaporator and Ambient Air Temperature Sensor Circuit Malfunction.

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 appropriate low reference circuit terminal and ground. Ambient air temperature sensor terminal B. Evaporator temperature sensor terminal 2. 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 appropriate signal circuit terminal. Ambient air temperature sensor terminal A. Evaporator temperature sensor terminal 1. 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 appropriate 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 low reference 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 low reference 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 low reference circuit terminal 2 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 2 and the signal circuit terminal 1. 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 inside air temperature sensor.

1. Test the appropriate air temperature sensor by varying the sensor temperature in water while monitoring the sensor resistance.
2. 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/sts/i-2007-2011/remont/automatic-hvac-system/#hvac-system-automatic)
2. «Inside Air Temperature Sensor Replacement»(/cadillac/sts/i-2007-2011/remont/automatic-hvac-system/#hvac-system-automatic)
3. «Sun Load Temperature Sensor Replacement»(/cadillac/sts/i-2007-2011/remont/automatic-hvac-system/#hvac-system-automatic)
4. «Control Module References»(/cadillac/sts/i-2007-2011/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 30 minutes.
2. The ambient air temperature is at least 21°C (70°F).
3. The A/C compressor operated for more than 2 minutes.
4. The system voltage is at least 12 volts.

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

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

Removal Procedure

1. Remove the ashtray. Refer to «Ashtray Replacement»(/cadillac/sts/i-2007-2011/remont/gauges-instrument-panels/#instrument-panel-trim-and-console-trim) .
2. Remove the radio. Refer to «Radio Replacement»(/cadillac/sts/i-2007-2011/remont/entertainment-systems/#cellular-system-entertainment-system-and-navigation-system) .
3. Remove the HVAC control module retaining screws.
4. Disconnect the HVAC control module electrical connectors.
5. Remove the HVAC control module.

Installation Procedure

1. Install the HVAC control module.
2. Connect the HVAC control module electrical connectors.
3. Install the HVAC control module retaining screws and tighten to 2 N.m (18 lb in).
4. Install the radio. Refer to «Radio Replacement»(/cadillac/sts/i-2007-2011/remont/entertainment-systems/#cellular-system-entertainment-system-and-navigation-system) .
5. Install the ashtray. Refer to «Ashtray Replacement»(/cadillac/sts/i-2007-2011/remont/gauges-instrument-panels/#instrument-panel-trim-and-console-trim) .
6. Refer to «Control Module References»(/cadillac/sts/i-2007-2011/remont/communication-devices/#programming-and-setup-all-systems__control-module-references) for programming and setup information.

Scheme 22

Scheme 23

1. Remove the air inlet assembly. Refer to «Air Inlet Assembly Replacement»(/cadillac/sts/i-2007-2011/remont/automatic-hvac-system/#heating-ventilation-and-air-conditioning) .
2. Disconnect the electrical connector from the recirculation actuator.
3. Remove the recirculation actuator screws (1).
4. Remove the recirculation actuator.

1. Install the recirculation actuator.
2. Install the recirculation actuator screws (1) and tighten to 1 N.m (9 lb in).
3. Connect the electrical connector to the recirculation actuator.
4. Install the air inlet assembly. Refer to «Air Inlet Assembly Replacement»(/cadillac/sts/i-2007-2011/remont/automatic-hvac-system/#heating-ventilation-and-air-conditioning) .

1. Remove the instrument panel (I/P) carrier. Refer to «Instrument Panel Carrier Replacement»(/cadillac/sts/i-2007-2011/remont/gauges-instrument-panels/#instrument-panel-trim-and-console-trim) .
2. Disconnect the mode actuator electrical connector.
3. Remove the mode actuator screws (3).
4. Remove the mode actuator.

1. Install the mode actuator.
2. Install the mode actuator screws (2) and tighten to 1 N.m (9 lb in ).
3. Connect the electrical connector to the actuator.
4. Install the I/P carrier. Refer to «Instrument Panel Carrier Replacement»(/cadillac/sts/i-2007-2011/remont/gauges-instrument-panels/#instrument-panel-trim-and-console-trim) .

1. Remove the air inlet assembly. Refer to «Air Inlet Assembly Replacement»(/cadillac/sts/i-2007-2011/remont/automatic-hvac-system/#heating-ventilation-and-air-conditioning) .
2. Remove the right air temperature actuator screws (1).
3. Remove the right air temperature actuator.
4. Disconnect the right air temperature actuator electrical connector.

1. Connect the right air temperature actuator electrical connector.
2. Install the right air temperature actuator.
3. Install the right air temperature actuator screws (1) and tighten to 1 N.m (9 lb in).
4. Install the air inlet assembly. Refer to «Air Inlet Assembly Replacement»(/cadillac/sts/i-2007-2011/remont/automatic-hvac-system/#heating-ventilation-and-air-conditioning) .

1. Remove the left closeout panel. Refer to «Instrument Panel Insulator Panel Replacement - Left Side»(/cadillac/sts/i-2007-2011/remont/gauges-instrument-panels/#instrument-panel-trim-and-console-trim) .
2. Disconnect the left air temperature actuator electrical connector from the actuator.
3. Remove the left air temperature actuator screws.
4. Remove the left air temperature actuator.

1. Install the left air temperature actuator.
2. Install the left air temperature actuator screws and tighten to 1 N.m (9 lb in).
3. Connect the left air temperature actuator electrical connector to the actuator.
4. Install the left closeout panel. Refer to «Instrument Panel Insulator Panel Replacement - Left Side»(/cadillac/sts/i-2007-2011/remont/gauges-instrument-panels/#instrument-panel-trim-and-console-trim) .

Scheme 24

Scheme 25

1. Remove the I/P cluster trim panel. Refer to «Instrument Cluster Trim Panel Replacement»(/cadillac/sts/i-2007-2011/remont/gauges-instrument-panels/#instrument-panel-trim-and-console-trim) .
2. Remove the knee bolster reinforcement. Refer to «Driver Knee Bolster Reinforcement Replacement»(/cadillac/sts/i-2007-2011/remont/gauges-instrument-panels/#instrument-panel-trim-and-console-trim) .
3. Disconnect the aspirator hose from the HVAC module.
4. Disconnect the aspirator hose from the inside air temperature sensor.
5. Remove the aspirator hose.

1. Install the aspirator hose.
2. Connect the aspirator hose to the inside air temperature sensor.
3. Connect the aspirator hose to the HVAC module.
4. Install the knee bolster reinforcement. Refer to «Driver Knee Bolster Reinforcement Replacement»(/cadillac/sts/i-2007-2011/remont/gauges-instrument-panels/#instrument-panel-trim-and-console-trim) .
5. Install the I/P cluster trim panel. Refer to «Instrument Cluster Trim Panel Replacement»(/cadillac/sts/i-2007-2011/remont/gauges-instrument-panels/#instrument-panel-trim-and-console-trim) .

1. Remove the HVAC module. Refer to «HVAC Module Assembly Replacement»(/cadillac/sts/i-2007-2011/remont/automatic-hvac-system/#heating-ventilation-and-air-conditioning) .
2. Disconnect all associated wiring connections attached to the HVAC module.
3. Remove heater core. Refer to «Heater Core Replacement»(/cadillac/sts/i-2007-2011/remont/automatic-hvac-system/#heating-ventilation-and-air-conditioning) .
4. Remove the right side air temperature actuator and linkage. Refer to «Temperature Valve Actuator Replacement - Right Side»(/cadillac/sts/i-2007-2011/remont/automatic-hvac-system/#hvac-system-automatic) .
5. Remove the HVAC module case screws.
6. Remove the HVAC module retainer clips.
7. Separate the HVAC module case.
8. Reposition the evaporator core to access the evaporator sensor.
9. Remove the evaporator sensor and harness from the evaporator core.

1. Add refrigerant oil to the evaporator core. Refer to «Refrigerant System Capacities»(/cadillac/sts/i-2007-2011/remont/automatic-hvac-system/#heating-ventilation-and-air-conditioning__refrigerant-system-capacities) .
2. Install the new evaporator core seals to evaporator.
3. Install the evaporator sensor and harness to the evaporator.
4. Install the evaporator core.
5. Connect the HVAC module case halves together.
6. Reposition and connect the HVAC Module wiring harness (1).
7. Install the HVAC module retainer clips.
8. Install the HVAC module case screws and tighten to 1 N.m (9 lb in).
9. Install the right side air temperature actuator and linkage. Refer to «Temperature Valve Actuator Replacement - Right Side»(/cadillac/sts/i-2007-2011/remont/automatic-hvac-system/#hvac-system-automatic) .
10. Install the heater core. Refer to «Heater Core Replacement»(/cadillac/sts/i-2007-2011/remont/automatic-hvac-system/#heating-ventilation-and-air-conditioning) .
11. Reconnect all associated wiring connections attached to the HVAC module.
12. Install the HVAC module. Refer to «HVAC Module Assembly Replacement»(/cadillac/sts/i-2007-2011/remont/automatic-hvac-system/#heating-ventilation-and-air-conditioning) .

Scheme 26

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

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

1. Remove the I/P cluster trim panel. Refer to «Instrument Cluster Trim Panel Replacement»(/cadillac/sts/i-2007-2011/remont/gauges-instrument-panels/#instrument-panel-trim-and-console-trim) .
2. Disconnect the aspirator hose (3) from the inside air temperature sensor (2).
3. Disconnect the electrical connector (1) from the inside air temperature sensor (2).
4. Disconnect the retaining clips and remove the inside air temperature sensor (2).

1. Install the inside air temperature sensor (2).
2. Connect the electrical connector (1) to the inside air temperature sensor (2).
3. Connect the aspirator hose (3) to the inside air temperature sensor (2).
4. Install the I/P cluster trim panel. Refer to «Instrument Cluster Trim Panel Replacement»(/cadillac/sts/i-2007-2011/remont/gauges-instrument-panels/#instrument-panel-trim-and-console-trim) .

1. Remove the defroster grille. Refer to «Defroster Grille Replacement»(/cadillac/sts/i-2007-2011/remont/automatic-hvac-system/#heating-ventilation-and-air-conditioning) .
2. Remove the sunload sensor from the defroster grill by twisting the sensor 1/4 turn counter clockwise.
3. Disconnect the sunload sensor electrical connector.
4. Remove the sunload sensor.

1. Connect the sunload sensor electrical connector.
2. Install the sunload sensor to the defroster grille by twisting the sensor 1/4 turn clockwise.
3. Install the defroster grille. Refer to «Defroster Grille Replacement»(/cadillac/sts/i-2007-2011/remont/automatic-hvac-system/#heating-ventilation-and-air-conditioning) .

HVAC Control Module

The HVAC control module is a GMLAN device that interfaces between the operator and the HVAC system to maintain air temperature and distribution settings. The battery positive voltage circuit provides power that the control module uses for keep alive memory (KAM). The instrument panel module (IPM), which is the vehicle power mode master, provides a device on signal. The control module supports the following features

Remote Start and Personalization

If the remote start personalization feature for climate control is selected through radio, the HVAC control module will receive information that defines the current driver of the vehicle from the Ezkey module through GMLAN communication. This information shall be stored inside the HVAC control module memory. When a different key fob is selected, the HVAC control module will recall the appropriate driver settings. The full auto mode and previous set temp will be commanded if ambient air temperature is above 0°C (32°F). Defrost mode will be commanded when the ambient air temperature is below 0°C (32°F). Upon a battery reset, the HVAC control module shall also set the driver ID to Driver#1. 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

If the remote start personalization feature for heated and vented seat control is selected through radio, if the inside air temperature is below 12°C (54°F) the heated seat will be commanded to high. If the inside air temperature is above 26°C (80°F) and the ambient air temperature is above 21°C (70°F) the vented seat will be commanded to high. When the HVAC control module is first turned On or key On, the last stored settings for the current driver will be activated, heat/vented seat control is carried over from remote start.

OnStar® Blower Control ON/OFF

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

All Air Temperature, Recirculation and Mode Actuators

The actuators are 5-wire bi-directional electric motors that incorporate 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 door position signal voltage is converted to a 0-255 count range. When the module sets a commanded, or targeted value, one of the control circuits is grounded. As the actuator shaft rotates the changing position signal is sent to the module. Once the position signal and the commanded value are the same, the module removes power and ground from the control circuits.

Air Temperature Sensors

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

1. Ambient
2. Inside

A signal and low reference circuit enables the sensor to operate. As the air temperature surrounding the sensor increases, the sensor resistance decreases. The sensor signal decreases as the resistance decreases. The sensor signal varies between 0-5 volts. The HVAC control module converts the signal to a range between 0-255 counts.

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

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

1. AUTO
2. A/C OFF
3. REAR DEFOGGER

Sunload Sensor

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

Evaporator Temperature Sensor

The HVAC control module monitors the temperature of the air passing through the evaporator by the A/C evaporator air temperature sensor. This sensor is located on the evaporator core. The temperature is used to cycle the A/C compressor ON and OFF to prevent the evaporator core from freezing. A thermistor inside the sensor varies its resistance to monitor the evaporator 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 serial data message to the engine control module (ECM) to stop requesting the A/C compressor clutch operation if the temperature drops below 3°C (37°F). The sensor must be above 4°C (39°F) to request the A/C compressor clutch again.

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

A/C Refrigerant Pressure Sensor

The A/C refrigerant pressure sensor is a 3-wire piezoelectric pressure transducer. A 5-volt reference, low reference, and signal circuits enable the sensor to operate. The A/C pressure signal can be between 0-5 volts. When the A/C refrigerant pressure is low, the signal value is near 0 volts. When the A/C refrigerant pressure is high, the signal value is near 5 volts.

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

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

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

As the requested blower speed increases, the following conditions occur

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

As the requested blower speed decreases, the following conditions occur

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

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.

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 Control Module References .

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

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

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

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

Air Distribution

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

Dual Zone Operation

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

Recirculation

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

Air Quality Sensor (RPO K14)

Warning - The air quality sensor recognizes carbon monoxide but is not designed as a safety feature to protect you from carbon monoxide. The air quality sensor is designed to limit your exposure to gasoline exhaust fumes and or diesel exhaust fumes that could enter into the passenger compartment from nearby vehicles for a limited amount of time.

The HVAC control module monitors the outside air quality while in AUTO mode via the air quality sensor assembly. You can activate the air quality sensor on your vehicle, if equipped, by pressing the Auto button on the HVAC module. The air quality sensor is a 5-wire sensor, 1 ignition voltage circuit, 2 ground circuit, and 2 control circuits. There are 2 sensors inside the air quality sensor assembly. A hydro carbon (HC) sensor that is used for detecting gasoline exhaust fumes and a Nox sensor that is used for detecting nitrous oxide, diesel exhaust fumes. The HVAC control module outputs a 5-volt signal on the HC and Nox control circuits and operates in a range between 0-5 volts.

The HVAC module updates the air quality sensor calibration approximately 4 times per second. The air quality sensor input to the HVAC module is compared to the previously updated air quality sensor calibration. If the voltage difference is great enough the recirc actuator will be controlled to recirc, outside air, or partial recirc outside air position based on the air quality sensor input.

When air quality around the front of the vehicle is poor, the air quality sensor system operates as follows

1. Poor air quality with high HC levels will cause the HC control circuit to read a lower voltage.
2. Poor air quality with high Nox levels will cause the Nox control circuit to read a higher voltage.
3. The recirculation actuator is forced to the recirculation position.
4. The recirc symbol on the HVAC module will illuminate.
5. The recirc icon will not illuminate if the recirc actuator is already in the auto recirc position.

When air quality around the front of the vehicle is normal, the air quality sensor system operates as follows

1. Normal air quality levels the HC control circuit will recognize very little voltage change from the previously updated calibration.
2. Normal air quality levels the Nox control circuit will recognize very little voltage change from the previously updated calibration.
3. The recirculation actuator position is not controlled by the air quality sensor system.

The following are conditions that will prevent the air quality sensor from controlling the recirc actuator

1. A/C OFF conditions (compressor OFF) prevents air quality sensor from changing the current position of the actuator)
2. Coolant temperature below 37°C (99°F) during warm up will prevent the blower from operating and air quality sensor from controlling the recirc position.
3. Outside air temperature less than 5°C (41°F) (prevents air quality sensor from changing the current position of the actuator)
4. Outside air temperature less than 15°C (59°F) and A/C high side pressure less than 196 kpa (28 psi) (prevents air quality sensor from changing the current position of the actuator)
5. 28 seconds sensor warm-up time after ignition is turned ON (prevents air quality sensor from changing the current position of the actuator)
6. Evaporator temperature sensor failure
7. Customer manually selects defrost or defog (forces actuator to outside air position)
8. Customer manually selects recirc or outside air position
9. Coolant temperature above 112°C (V8), 119°C (HFV6) the actuator is forced to the recirc position. When coolant temperature drops below 109°C (V8), 116°C (HFV6) forced recirc is canceled.
10. A/C pressure above 2 500 KPA (362 psi) the actuator is forces to the recirc position. When A/C pressure drops below 2 000 KPA (290 psi) forced recirc is canceled.

The following describes the recirc actuator function after the air quality sensor has canceled the command to recirc

1. Full recirc position will be held for 2 minutes when vehicle speed is less than 10 km/h (6.3 mph) after 2 minutes expires the recirc door will move to full outside air position.
2. Partial recirc, outside air position will be held for 2 minutes when vehicle speed is above 20 km/h (12.5 mph) after 2 minutes expires the recirc door will move to full outside air position.
3. Full outside air position if vehicle speed is greater than 60 km/h (37 mph) and blower is not on high speed.

The instrument panel module (IPM) shall provide the GMLAN Option Information for "Climate Air Quality Sensor Present" and "Climate Control Air Quality Sensitivity Selection" to the HVAC control module. Based on the option information sent to the HVAC control module by the IPM, the HVAC control module will choose 1 of 7 different sensitivity calibration settings stored in the HVAC module. The IPM sends the signal that tells the HVAC control module which sensitivity setting to use. From production the IPM sends a GMLAN message of 0 which tells the HVAC control module to use the default level 4 sensitivity calibration. The air quality sensitivity message sent to the HVAC module can be changed through the IPM with a TECH 2 and has 7 different air quality sensor calibration settings to choose from, 1 being the most sensitive to exhaust fumes and 7 being the least sensitive to exhaust fumes.

The driver information center (DIC) will display the SERVICE A/C SYSTEM message if the HVAC system has detected a short to ground in the air quality sensor circuit. An open circuit or a short to voltage in the air quality sensor circuit will be diagnosed through symptom based diagnostics because both of these conditions will not turn on the SERVICE A/C SYSTEM message or set a trouble code.

Heating and A/C Operation

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

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

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

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

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

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

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

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

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

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

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

Automatic Operation

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

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

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

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

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

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

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

Auxiliary HVAC Control Module

The auxiliary HVAC control module is a non-GM LAN device that interfaces between the operator and the auxiliary HVAC system to maintain air temperature and air distribution settings. Airflow to the rear system will be turned off when defrost is selected on the front HVAC control module to direct air to clear the windshield. Auxiliary HVAC temperatures can be set cooler or warmer than the front primary HVAC setting. 5 volts and ground are supplied to the rear HVAC control module from the front 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.

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
• Checking Aftermarket Accessories
• Service Programming System (SPS)
• Ashtray Replacement
• Radio Replacement
• Fastener Caution
• Refrigerant System Capacities
• DTC B0158 or B0163
• Sensor Resistance Table
• Fastener Tightening Specifications