Air Conditioning Compressor Malfunction
Air Conditioning Compressor Malfunction
Diagnostic Instructions
* Perform the Diagnostic System Check - Vehicle Diagnostic System Check - Vehicle prior to using this diagnostic procedure.
* Review Strategy Based Diagnosis Strategy Based Diagnosis for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions Diagnostic Procedure Instructions provides an overview of each diagnostic category.
Diagnostic Fault Information
Circuit/System Description
When the A/C switch is pressed, the HVAC control module grounds the A/C request signal circuit. This input will request the engine control module (ECM) to ground the A/C compressor clutch relay control circuit, which will switch the A/C COMP 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 ECM to turn on the compressor clutch:
* Battery voltage is between 9-18 volts.
* Engine coolant temperature (ECT) is less than 123°C (253°F).
* Engine speed is less than 4,760 RPM.
* Engine speed is more than 600 RPM.
* A/C high side pressure is between 2929-269 kPa (425-39 psi).
* Throttle position is less than 100 percent.
* Evaporator temperature is greater than 0°C (32°F).
* ECM does not detect excessive torque load.
* ECM does not detect insufficient idle quality.
Reference Information
Schematic Reference
HVAC Schematics Electrical Diagrams
Connector End View Reference
Component Connector End Views 5 Bow Lowered Switch (CM7)
Description and Operation
Automatic HVAC Description and Operation Description and Operation
Electrical Information Reference
* Circuit Testing Circuit Testing
* Connector Repairs Connector Repairs
* Testing for Intermittent Conditions and Poor Connections Testing for Intermittent Conditions and Poor Connections
* Wiring Repairs Wiring Repairs
Scan Tool Reference
Control Module References Control Module References for scan tool information
Circuit/System Verification
Engine running, observe the function of the A/C compressor clutch while commanding the A/C relay ON and OFF with a scan tool. The A/C compressor clutch should engage and disengage.
Circuit/System Testing
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 H9 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 F9 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 COMP relay.
4. Verify that a test lamp illuminates between the B+ circuit terminal F8 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 for a short to ground.
5. Disconnect the harness connector at the A/C compressor clutch.
6. Test for less than 1.0 ohm between the ground circuit terminal A 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 F8 and the control circuit terminal H9. 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.
9. Connect a test lamp between the ignition circuit terminal F9 and the control circuit terminal H8.
10. 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.
11. If all circuits test normal, test or replace the A/C COMP relay.
Component Testing
Relay Test
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 30-amp 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.
Repair Instructions
Perform the Diagnostic Repair Verification Verification Tests after completing the diagnostic procedure.
* Relay Replacement (Attached to Wire Harness) Relay Replacement (Attached to Wire Harness)Relay Replacement (Within an Electrical Center) Relay Replacement (Within an Electrical Center)
* Air Conditioning Compressor Replacement Removal and Replacement
* Control Module References Control Module References for ECM replacement, setup, and programming