Chart C-10, A/C Compressor Clutch Circuit Diagnosis: Notes

The Powertrain Control Module (PCM) delays A/C clutch relay engagement to allow Engine Control Module (ECM) to adjust engine RPM before the clutch engages. When A/C is turned on, a 12-volt signal is sent to PCM. PCM grounds circuit No. 459 to energize A/C clutch relay. PCM will engage A/C clutch whenever A/C has been requested unless any of following conditions exists.

• High coolant temperature
• Wide open throttle
• Low or high A/C system pressure
• High engine RPM

If sensor wire becomes open, shorted to ground, or shorted to voltage, Diagnostic Trouble Code (DTC) 66 will set. If A/C clutch engages and no pressure change is detected, DTC 67 will set. When A/C request has been detected by PCM, cooling fans will be turned on unless vehicle speed is too high.

1. Checks ability of PCM to control A/C clutch relay.
2. Checks for short to voltage on circuit No. 762, faulty PCM, or faulty A/C-heater control.
3. Checks for shorted circuit No. 459 to PCM.