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 Compressor Clutch Relay Coil Ignition | P0646 | P0645, P0646 | -- | -- |
A/C Compressor Clutch Relay Switch B+ | 1 | 1 | -- | -- |
A/C Compressor Clutch Relay Coil Control | P0646 | P0645, P0646 | P0647 | 3 |
A/C Compressor Control | 1 | 1 | 2 | -- |
A/C Compressor Ground | 1 | 1 | -- | -- |
| ||||
Circuit/System Description
When the A/C switch is pressed, the HVAC control module sends an A/C request message to the engine control module (ECM) via CAN-Bus. Therefore the ECM grounds the A/C compressor clutch relay control circuit, which will switch the A/C compressor clutch relay. With the relay contacts closed, battery voltage is supplied to the A/C compressor clutch. The A/C compressor clutch will be activated.
Diagnostic Aids
The following conditions must be met in order to activate the A/C compressor:
| • | Battery voltage is between 9-18 V |
| • | Engine coolant temperature is less than 124°C (255°F) |
| • | Engine speed is greater than 600 RPM |
| • | Engine speed is less than 5 500 RPM |
| • | A/C high side pressure is between 269-2 929 kPa (39-425 PSI) |
| • | Throttle position is less than 100% |
| • | Evaporator temperature is greater than 3°C (38°F) |
| • | ECM does not detect immoderate torque load |
| • | ECM does not detect insufficient idle quality |
| • | The ambient temperature is above 1°C (34°F) |
Reference Information
Schematic Reference
LINK 49327
Connector End View Reference
Description and Operation
Automatic HVAC Description and Operation
Electrical Information Reference
Scan Tool Reference
Control Module References for scan tool information
Circuit/System Testing
Note: Before executing Circuit/System Testing, all conditions shown in Diagnostic Aids must be met.
- Ignition ON, press and release the A/C switch. Verify the scan tool A/C Switch parameter changes between Active and Inactive.
- Activate and deactivate the A/C compressor with the A/C switch. Verify the engine control module (ECM) scan tool A/C Request Signal parameter changes between Active and Inactive.
- Ignition OFF, disconnect the KR29 A/C Compressor Clutch Relay.
- Ignition ON, verify that a test lamp illuminates between the B+ circuit terminal 30 and ground.
- Verify that a test lamp does not illuminate between the control circuit terminal 87 and ground.
- Ignition OFF, disconnect the harness connector at the Q2 A/C Compressor Clutch.
- Test for less than 5 Ω between the Q2 A/C Compressor Clutch ground circuit terminal A and ground.
- Connect the harness connector at the Q2 A/C Compressor Clutch.
- Ignition ON, connect a 10 A fused jumper wire between the B+ circuit terminal 30 and the control circuit terminal 87. Verify the Q2 A/C Compressor Clutch is activated.
- Connect a test lamp between the ignition circuit terminal 85 and the control circuit terminal 86.
- Command the engine control module (ECM) A/C Relay output function ON and OFF with the scan tool. The test lamp should turn ON and OFF when changing between the commanded states.
- If all circuits test normal, replace the KR29 A/C Compressor Clutch Relay.
| ⇒ | If not the specified value, replace the A26 HVAC Control. |
| ⇒ | If not the specified value, replace the K33 HVAC Control Module. |
| ⇒ | If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance. |
| ⇒ | If the test lamp illuminates, test the control circuit for a short to voltage. |
| ⇒ | If greater than the specified value, test the ground circuit for an open/high resistance. |
| ⇒ | If the Q2 A/C Compressor Clutch does not activate, test the control circuit for an open/high resistance. If the circuit test normal, replace the Q2 A/C Compressor Clutch. |
| ⇒ | If the test lamp always illuminates or always does not illuminate, replace the K20 Engine Control Module. |
Repair Instructions
Perform the Diagnostic Repair Verification after completing the diagnostic procedure.
| • | LINK 63253 |
| • | Control Module References for HVAC Control Module or Engine Control Module replacement, setup, and programming |
