Chevrolet Trax: 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.

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 is above 1ºC (34ºF).
• Blower motor ON

Reference Information

Schematic Reference

HVAC Schematics (Encore)

Connector End View Reference

WIRING SYSTEMS AND POWER MANAGEMENT - COMPONENT CONNECTOR END VIEWS - INDEX - ENCORE WIRING SYSTEMS AND POWER MANAGEMENT - COMPONENT CONNECTOR END VIEWS - INDEX - TRAX

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.

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 engine control module (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.

If the parameter changes

6. Verify the A/C compressor clutch engages when commanding the engine control module (ECM) A/C Relay output function On and Off with a scan tool.

If the A/C compressor clutch does not engage

Refer to DTC P0645, P0646, or P0647

If the A/C compressor clutch engages

7. 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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