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

A/C compressor clutch relay is controlled by the Powertrain Control Module (PCM). The PCM provides a ground on circuit No. 459 when A/C is requested. PCM will delay A/C compressor clutch engagement momentarily after A/C is requested. This delay allows Idle Air Control (IAC) valve to adjust engine RPM for additional load.

PCM will temporarily disengage A/C compressor for a precalibrated time during one or more of the following conditions: Wide Open Throttle (WOT), engine coolant temperature greater than 250°F (121°C) or engine RPM greater than 4800 RPM.

1. A/C clutch should not engage with engine running if an A/C mode is not selected at control head.
2. Compressor clutch should apply if intake air temperature is greater than 60°F (15.5°C) or engine coolant temperature is less than 246°F (119°C).
3. Checks for an A/C request signal from control head to PCM.
4. Checks for an A/C request signal to A/C high pressure cut-out switch.
5. Checks for ignition voltage on circuit No. 739 and PCM control of ground circuit No. 459 to A/C relay coil.
6. Checks for ignition voltage on circuit No. 739 to A/C relay contacts.
7. Determines whether A/C relay, compressor clutch coil or circuitry is at fault.
8. Determines if PCM is turning on A/C relay due to false A/C request.
9. Determines whether problem is in A/C control head and circuits No. 66 and 257 to pressure cycling switch, or circuit No. 67 and PCM.
10. Checks for short to battery voltage in circuit No. 59 or faulty compressor clutch.
11. Determines if A/C relay is faulty or AC relay control circuit No. 459 is grounded at all times.