For 1990-2009 cars only
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. |
Diagnostic Fault Information
Circuit | Short to Ground | Open/High Resistance | Short to Voltage | Signal Performance |
|---|---|---|---|---|
Relay Switch B+ | 1 | 1 | -- | -- |
Relay Coil Ignition Voltage | 1 | 1 | -- | -- |
A/C Compressor Clutch Relay Control | P0645 | P0645 | P0645 | -- |
Relay Coil Ground | -- | 1 | -- | -- |
Compressor Clutch Ground | -- | 1 | -- | -- |
1. A/C Compressor Malfunction | ||||
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 CMPRSR CLUTCH relay on. 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 greater than 600 RPM |
| • | Engine speed is less than 4,760 RPM |
| • | A/C high side pressure is between 2929-269 kPa (39-425 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 |
| • | The ambient temperature is above 1°C (34°F) |
Reference Information
Schematic Reference
Connector End View Reference
Description and Operation
Electrical Information Reference
Scan Tool Reference
Control Module References for scan tool information
Circuit/System Verification
- Engine running
- Press the A/C request switch. The A/C compressor clutch should engage.
- 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 |
Circuit/System Testing
- Ignition OFF, disconnect the X2 harness connector at the HVAC control module.
- Test for less than 1.0 ohm between the ground circuit terminal and ground.
- Remove the A/C compressor clutch relay.
- Verify that a test lamp illuminates between the ignition circuit terminal 85 and ground.
- Verify that a test lamp illuminates between the B+ circuit terminal 30 and ground.
- Disconnect the harness connector at the A/C compressor clutch.
- Ignition OFF test for less than 1.0 ohm between the A/C compressor ground circuit terminal 2 and ground.
- Connect the harness connector at the A/C compressor clutch.
- Connect a 10-amp fused jumper wire between the B+ circuit terminal 30 and the control circuit terminal 87. Verify the A/C compressor clutch engages.
- Connect a test lamp between the control circuit terminal 86 and the B+ circuit terminal 85.
- Using a scan tool, command the A/C relay output ON and OFF. The test lamp should turn ON and OFF when changing between the commanded states.
- If all circuits test normal, test or replace the A/C compressor.
| ⇒ | If greater than the specified range, test the ground circuit for an open/high resistance. |
| ⇒ | If the test lamp does not illuminate, test the ignition circuit for a short to ground or an open/high resistance. |
| ⇒ | If the test lamp does not illuminate, test the B+ circuit for an open/high resistance. If the A/C clutch fuse is open, test the relay switch control circuit for a short to ground. If all circuits test normal, test or replace the A/C compressor clutch. |
| ⇒ | If greater than the specified range, test the ground circuit for an open/high resistance. |
| ⇒ | 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. |
| ⇒ | If the test lamp remains ON all the time, test the control circuit for a short to ground. If the circuit tests normal, replace the ECM. |
| ⇒ | If the test lamp remains OFF all the time, test the control circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the ECM. |
Repair Instructions
Perform the Diagnostic Repair Verification after completing the diagnostic procedure.
| • | Control Module References for HVAC control module and ECM replacement, setup, and programming |
