Compressor Clutch Does Not Engage

HVAC COMPRESSOR CLUTCH DOES NOT ENGAGE

Diagnostic Fault Information
Perform the Diagnostic System Check - HVAC Systems - Manual prior to using this diagnostic procedure. Initial Inspection and Diagnostic Overview

Circuit/System Description
When the A/C switch is pressed, the HVAC control assembly applies B+ to the A/C request signal circuit. The body control module (BCM) receives this input and sends a class 2 message to the powertrain control module (PCM) for an A/C request. This input will request the PCM 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.

Diagnostic Aids
The following conditions must be met in order for the PCM to turn on the compressor clutch:
• Battery voltage is between 9-16 volts.
• Engine coolant temperature (ECT) is less than 124°C (255°F).
• Engine speed is less than 5480 RPM.
• Engine speed is more than 600 RPM.
• A/C high side pressure is between 3034-241 kPa (440-35 psi).
• Throttle position is less than 100 percent.
• PCM does not detect excessive torque load
• PCM does not detect insufficient idle quality.

Reference Information
HVAC Schematics Electrical Diagrams
HVAC Connector End Views Connector Views

Electrical Information Reference Diagnostic Aids
• Circuit Testing
• Connector Repairs
• Testing for Intermittent Conditions and Poor Connections
• Wiring Repairs

Scan Tool Reference Scan Tool Testing and Procedures
• Scan Tool Data List
• Scan Tool Data Definitions
• Scan Tool Output Controls

Circuit/System Verification
1. Press the A/C request switch. The A/C compressor clutch should engage.
2. Place the mode switch in the defrost position. The A/C compressor clutch should engage.

Circuit/System Testing
1. Ignition OFF, disconnect the harness connector at the HVAC control module.

2. Ignition OFF, test for less than 1.0 ohm of resistance between the ground circuit terminal A5 and ground.
If greater than 1.0 ohm, test the ground circuit for an open/high resistance.

3. Ignition ON, test for B+ between the ignition circuit terminal A4 and ground.
If less than B+, test the ignition circuit for an open/high resistance. If the A/C CRUISE fuse is open, test ignition circuit for a short to ground.

4. Install a 3-amp fused jumper wire between the signal circuit terminal A1 and B+. With a scan tool, verify the BCM A/C Switch parameter is ON.
If not the specified value, test the signal circuit for a short to ground or an open/high resistance. If circuit tests normal, replace the BCM.

5. Reconnect the harness connector of the HVAC control module. With a scan tool, verify the BCM A/C Switch parameter cycles between On and Off with each press of the A/C switch.
If the parameter does not cycle, test the signal circuit for a short to B+. If the circuit tests normal, test or replace the HVAC control module.

6. Remove the A/C compressor clutch relay.

7. Verify that a test lamp illuminates between the ignition circuit terminal F11 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 the ignition circuit fuse is open, test or replace the A/C compressor relay.

8. Verify that a test lamp illuminates between the B+, circuit terminal F9 and ground.
If the test lamp does not illuminate, test the B+, circuit for a short to ground or an open/high resistance. If the circuit tests normal and the B+, circuit fuse is open, test the control circuit terminal E11 for a short to ground.

9. Disconnect the harness connector at the A/C compressor clutch.

10. Test for less than 1.0 ohm of resistance between the A/C compressor clutch ground circuit terminal A and ground.
If greater than the specified range, test the ground circuit for an open/high resistance.

11. Connect the harness connector at the A/C compressor clutch.

12. Connect a 10A fused jumper wire between the B+, circuit terminal F9 and the control circuit terminal E11. Verify the A/C compressor clutch is activated
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 clutch.

13. Connect a test lamp between the ignition circuit terminal F11 and the control circuit terminal E9.

14. Command the A/C compressor clutch 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 PCM.

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 PCM.

15. If all circuits test normal, test or replace the A/C compressor relay.

Repair Instructions
• Powertrain Control Module Replacement Service and Repair
• Body Control Module Replacement Service and Repair
• Heater and Air Conditioning Control Replacement Service and Repair
• Air Conditioning Clutch Coil Removal Compressor Clutch Coil