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 |
|---|---|---|---|---|
A/C Relay Switch B+ | 1 | 1 | -- | -- |
A/C Relay Coil Ignition | 1 | 1 | -- | -- |
A/C Relay Switched Output Control | 1 | 1 | 2 | -- |
A/C Compressor Clutch Relay Control | P0645 | P0645 | P0645 | -- |
A/C Compressor Clutch Ground | -- | 1 | -- | -- |
1. A/C Compressor Inoperative 2. A/C Compressor Always On | ||||
Circuit System Description
When the A/C switch is pressed, the HVAC control module sends a serial data message to the ECM. 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) Air Conditioning (A/C) System Performance Test |
| • | 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 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 A/C relay.
- Ignition ON, verify that a test lamp does not illuminate between the control circuit terminal 86 and ground.
- Verify that a test lamp illuminates between the ignition circuit terminal 85 and ground.
- Verify that a test lamp illuminates between the relay B+ circuit terminal 30 and ground.
- Disconnect the harness connector at the A/C clutch coil.
- Test for less than 1 ohm between the ground circuit terminal ground.
- Connect the harness connector at the A/C clutch coil.
- 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.
- Connect a test lamp between the ignition circuit terminal 85 and the control circuit terminal 86.
- 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 all circuits test normal, test or replace the A/C clutch relay.
| ⇒ | If the test lamp illuminates, test the control circuit for a short to voltage. |
| ⇒ | 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. |
| ⇒ | 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. |
| ⇒ | If greater than the specified range, test the ground circuit for an open/high resistance. |
| ⇒ | 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. |
| ⇒ | 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. |
Component Testing
Relay Test
- Ignition OFF, disconnect the A/C relay.
- Test for 60-200 ohms between terminal 85 and 86.
- Test for infinite resistance between the following terminals:
- Install a 15A 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 the resistance is not within the specified range, replace the relay. |
| • | 30 and 86 |
| • | 30 and 87 |
| • | 30 and 85 |
| • | 85 and 87 |
| ⇒ | If not the specified value, replace the relay. |
| ⇒ | If greater than the specified range, replace the relay. |
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 |
