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 engine control module (ECM) to ground the A/C compressor clutch relay control circuit, which will switch the A/C 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
Description and Operation
Air Temperature Description and Operation
Electrical Information Reference
Scan Tool Reference
Scan Tool Data List
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 A/C CLUTCH relay.
- Ignition ON, verify that a test lamp does not illuminate between the control circuit terminal and ground.
| ⇒ | If the test lamp illuminates, test the control circuit for a short to voltage. |
- Verify that a test lamp illuminates between the ignition circuit terminal and ground.
| ⇒ | If the test lamp does not illuminate, test the ignition circuit for a short to ground or an open/high resistance. If the circuit tests normal and the ignition circuit fuse is open, test or replace the A/C CLUTCH relay. |
- Verify that a test lamp illuminates between the B+ circuit terminal and ground.
| ⇒ | If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance. If the circuit tests normal and the B+ circuit fuse is open, test the control circuit terminal for a short to ground. |
- Disconnect the harness connector at the A/C compressor clutch.
- Test for less than 1.0 ohm of resistance between the A/C compressor clutch ground circuit terminal A 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 10A fused jumper wire between the B+ circuit terminal and the control circuit terminal. Verify the A/C compressor clutch is activated.
| ⇒ | 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 clutch |
- Connect a test lamp between the ignition circuit terminal and the control circuit terminal.
- Command the A/C relay 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. |
- If all circuits test normal, test or replace the A/C CLUTCH relay.
Repair Instructions
Perform the
Diagnostic Repair Verification
after completing the diagnostic procedure.
Control Module References
for ECM replacement, setup, and programming
