Chart C-10 A/C Clutch Control Circuit Diagnosis

A/C Clutch Control Wiring Circuit:

Circuit Description:

The A/C relay is PCM controlled to delay A/C clutch engagement .4 second after A/C is turned "ON." This allows the IAC to adjust engine RPM before the A/C clutch engages. The PCM also causes the relay to disengage the A/C clutch during WOT operation. The A/C relay is energized when the PCM provides a ground path for CKT 459. The PCM may apply the A/C clutch during cranking to prevent A/C slugging during start-up.

Test Description: Number(s) below refer to circled number(s) on the diagnostic chart.

PART 1 OF 3

Chart C-10 - A/C Clutch Circuit Diagnosis:

1. A/C clutch should not be engaged with the engine running if an A/C mode is not selected at the control head.
2. Compressor clutch should apply if the conditions under the NOTICE at the top of the chart have been met.
3. Checks for an A/C request signal from the control head to the pressure cycling switch.

PART 2 OF 3

Chart C-10 - A/C Clutch Circuit Diagnosis (Part 2 Of 3):

4. Checks for ignition voltage (CKT 639) and PCM control of the ground (CKT 366) to the A/C relay coil.
5. Checks for ignition voltage (CKT 639) to the A/C relay contacts.
6. Determines whether the A/C relay or the compressor clutch coil or circuitry is at fault.

PART 3 OF 3

Chart C-10 - A/C Clutch Circuit Diagnosis (Part 3 Of 3):

2. Determines whether or not the PCM is turning the A/C relay "ON" due to a false A/C request.
3. Isolates problem to the A/C control head and CKTs 257 and 66 to the pressure cycling switch or CKT 67 and the PCM.
4. Checks for CKT 59 shorted to B+ or a faulty compressor clutch.
5. Determines whether the A/C relay is faulty or the A/C relay control circuit (CKT 459) is grounded all the time.