Buick Regal: Air Conditioning Compressor Malfunction

Diagnostic Instructions

• Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.
• Review Strategy Based Diagnosis for an overview of the diagnostic approach.
• Diagnostic Procedure Instructions provides an overview of each diagnostic category.

Circuit/System Description

The A/C compressor uses a conventional belt driven magnetic clutch to engage and mechanically turn the compressor. When the A/C switch is pressed, the HVAC control module sends an A/C request message to the ECM via serial data. If specific criteria is met, the ECM then grounds the A/C compressor clutch relay control circuit, which will switch the A/C compressor clutch relay. With the relay contacts closed, battery voltage is supplied to the permanently grounded A/C compressor clutch.

The A/C compressor clutch will then be activated.

This A/C system utilizes a variable displacement solenoid valve to alter the amount of displacement created by the turning of the compressor. The HVAC control module provides both battery voltage and a pulse width modulated ground to the variable displacement solenoid valve. When the A/C switch is pressed, the HVAC control module grounds the variable displacement solenoid using a (PWM) signal in order to determine the amount of compressor displacement. The performance of the A/C compressor is regulated based on the adjusted interior temperature.

Diagnostic Aids

The following conditions must be met in order to turn on the A/C compressor:

• Battery voltage is between 9 - 18 V.
• Engine coolant temperature is less than 124ºC (255ºF).
• Engine speed is greater than 600 RPM.
• Engine speed is less than 5 500 RPM.
• A/C high side pressure is between 269 - 2 929 kPa (39 - 425 PSI).
• Throttle position is less than 100%.
• Evaporator temperature is greater than 3ºC (38ºF).
• ECM does not detect excessive torque load.
• ECM does not detect insufficient idle quality.
• The ambient temperature sensor senses above 1ºC (34ºF).
• Blower motor is ON.

Reference Information

Schematic Reference

HVAC Wiring Schematics

Connector End View Reference

Component Connector End View Index

Description and Operation

Automatic HVAC Description and Operation

Electrical Information Reference

• Circuit Testing
• Connector Repairs
• Testing for Intermittent Conditions and Poor Connections
• Wiring Repairs

Scan Tool Reference

Control Module References for scan tool information

Circuit/System Verification

NOTE: Refer to HVAC System Malfunction before performing this procedure.

1. Ignition ON, press and release the A/C Switch.

2. Verify the HVAC control module scan tool A/C Switch parameter changes between Active and Inactive.

• If the parameter does not change

Replace the A26 HVAC Controls.

• Go to next step: If the parameter changes

3. Set A/C system to coolest setting with blower ON.

4. Press and release the A/C switch several times.

5. Verify the ECM scan tool A/C Request Signal parameter changes between Active and Inactive.

• If the parameter does not change

Replace the K33 HVAC Control Module.

• Go to next step: If the parameter changes

6. Verify the A/C compressor clutch engages and disengages when commanding the ECM A/C Relay output function On and Off with a scan tool.

• If the A/C compressor clutch does not engage or disengage as commanded

Refer to DTC P0645, P0646, or P0647

• Go to next step: If the A/C compressor clutch engages and disengages as commanded

7. Engine ON.

8. Verify the HVAC control module scan tool A/C Compressor Refrigerant Solenoid Valve Command parameter changes with varying cooling loads.

• If the parameter does not change

Refer to DTC B393B

• Go to next step: If the parameter does change

9. All OK.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the repair.

• HVAC Component Replacement Reference
• Control Module References for HVAC control module replacement, programming and setup

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