Air Conditioning Compressor Malfunction
Air Conditioning Compressor Malfunction
Diagnostic Instructions
* Perform the Diagnostic System Check - Vehicle (Initial Inspection and Diagnostic Overview) prior to using this diagnostic procedure.
* Review Strategy Based Diagnosis (Initial Inspection and Diagnostic Overview) for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions (Initial Inspection and Diagnostic Overview) provides an overview of each diagnostic category.
Diagnostic Fault Information
Circuit/System Description
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 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 (Connector Views)
Description and Operation
* Air Delivery Description and Operation (Air Delivery Description and Operation)
* Air Temperature Description and Operation (Air Temperature Description and Operation)
Electrical Information Reference
* Circuit Testing (Component Tests and General Diagnostics)
* Connector Repairs (Component Tests and General Diagnostics)
* Testing for Intermittent Conditions and Poor Connections (Component Tests and General Diagnostics)
* Wiring Repairs (Component Tests and General Diagnostics)
Scan Tool Reference
Control Module References (Programming and Relearning) for scan tool information
Circuit/System Verification
1. Engine running, 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.
• If the clutch does not engage refer to Air Conditioning (A/C) System Performance Test (Initial Inspection and Diagnostic Overview) .
Circuit/System Testing
1. Ignition OFF, disconnect the harness connector at the A/C low pressure switch.
2. Test for less than 5 ohms between the ground circuit terminal B and ground.
• If greater than the specified range, test the ground circuit for an open/high resistance.
3. Ignition ON, verify the scan tool Low Pressure Switch parameter is Open.
• If not the specified value, test the signal circuit terminal A for a short to ground. If the circuit tests normal, replace the HVAC control module.
4. Connect a 3-amp fused jumper wire between the signal circuit terminal A and ground. Verify the scan tool Low Pressure Switch parameter is Closed.
• If not the specified value, 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. Connect the harness connector at the A/C low pressure switch. Verify the scan tool Low Pressure Switch parameter is Closed.
• If not the specified value, test or replace the A/C low pressure switch.
6. Ignition OFF, disconnect the A/C relay.
7. 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.
8. Verify that a test lamp illuminates between the ignition circuit terminal 85 and ground.
• If the test lamp does not illuminate, test the ignition circuit for a short to ground or a open/high resistance. If the circuit tests normal and ignition circuit fuse is open, test all components connected to the ignition circuit and replace as necessary.
9. Verify that a test lamp illuminates between the relay B+ circuit terminal 30 and ground.
• If the test lamp does not illuminate, test the B+ circuit for a short to ground or a open/high resistance. If the circuit tests normal and B+ circuit fuse is open, replace the A/C clutch relay.
10. Disconnect the harness connector at the A/C clutch coil.
11. Test for less than 1 ohm between the ground circuit terminal 2 and ground.
• If greater than the specified range, test the ground circuit for an open/high resistance.
12. Connect the harness connector at the A/C clutch coil.
13. Connect a 10-amp fused jumper wire between the B+ circuit terminal 30 and control circuit terminal 87. Verify the A/C clutch is activated.
• If the A/C clutch does not activate, test the control circuit for an open/high resistance. If the circuit tests normal, test or replace the A/C clutch.
14. Connect a test lamp between the ignition circuit terminal 85 and the control circuit terminal 86.
15. Command the A/C relay output function 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.
16. If all circuits test normal, test or replace the A/C clutch relay.
Repair Instructions
Perform the Diagnostic Repair Verification (Verification Tests) after completing the diagnostic procedure.
* Compressor Clutch Assembly Replacement (Service and Repair)
* Heater and Air Conditioning Control Replacement (Service and Repair)