A/C Signal: Testing and Inspection

A/C Compressor Control Circuit Diagnosis





Circuit Description
The VCM control of the A/C clutch improves idle quality and performance by performing the following conditions:
- Delaying clutch engagement until the idle speed is increased
- Releasing the clutch when the idle speed is too low
- Providing additional fuel at the instant the clutch is applied
The additional fuel smooths the cycling of the compressor.
Turning the air conditioning ON supplies battery voltage through the pressure switches to the VCM. When the VCM receives the voltage on the A/C request signal, the NC enable relay circuit is grounded. The A/C compressor clutch then engages.

Test Description











The numbers below refer to the step numbers on the diagnostic table.
2. Checks for low refrigerant as the cause for no A/C.
3. This and the following tests, check for a faulty A/C control relay and high and low cutout switches.