Diagnostic Instructions
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 ECM to ground the A/C compressor clutch relay control circuit, which will switch the A/C CMPRSR CLUTCH 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
Connector End View Reference
HVAC Connector End Views
Electrical Information Reference
Scan Tool Reference
Circuit/System Verification
- Ignition ON, 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.
Circuit/System Testing
- Ignition OFF, disconnect the harness connector X2 terminal 8 ground circuit terminal at the HVAC control module.
- Ignition OFF, test for less than 1.0 ohm of resistance between the ground circuit terminal and ground.
| ⇒ | If greater than the specified, test the ground circuit for an open/high resistance. |
- Remove the A/C compressor clutch relay.
- Verify that a test lamp illuminates between the relay coil B+ circuit terminal 85 and ground.
| ⇒ | If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance. |
- Verify that a test lamp illuminates between the relay switch B+ circuit terminal 30 and ground.
| ⇒ | If the test lamp does not illuminate, test the relay switch 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. |
- Disconnect the harness connector at the A/C compressor clutch terminal 1.
- Ignition OFF test for less than 1.0 ohm of resistance between the A/C compressor ground circuit terminal 2 and ground.
| ⇒ | If greater than the specified range, test the ground circuit for an open/high resistance. |
- Connect the harness connector at the A/C compressor clutch.
- Connect a 10-amp fused jumper wire between the relay switch B+ circuit terminal 30 and the relay switch control circuit terminal 87. Verify the A/C compressor clutch engages.
| ⇒ | 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. |
- Connect a test lamp between the relay control circuit terminal 86 and the relay coil 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 the test lamp remains ON all the time, test for a short to ground on the control circuit connector X1 terminal 53. If the circuit tests normal, replace the ECM. |
| ⇒ | If the test lamp remains OFF all the time,
test for a short to voltage or an open/high resistance on the control circuit. If the circuit tests normal, replace the ECM. |
- If all circuits test normal, test or replace the A/C compressor.
Repair Instructions
Perform the
Diagnostic Repair Verification
after completing the diagnostic procedure.
