Part 1 of 2

A/C Clutch Control Diagnosis (Part 1 Of 2):

A/C Clutch Control Diagnosis:

CIRCUIT DESCRIPTION
When the A/C control switch is turned "ON," voltage is supplied to the Vehicle Control Module-A (VCM-A) on CKT 66. If there is sufficient pressure in the A/C system and/or the ambient temperature is not too cold, the A/C pressure switch will close and supply voltage to the switch side of the A/C relay on CKT 901. After a calibrated delay time (approximately 20 sec), the VCM-A will ground CKT 459, enabling the relay and applying voltage to CKT 248. The normally closed A/C high pressure cutoff switch will provide voltage to CKT 59 and enable the A/C clutch. Voltage is also supplied to the VCM-A on CKT 59. This voltage signal allows the VCM-A to make idle, timing and fuel corrections for smoother clutch engagements.

CHART TEST DESCRIPTION
Number(s) below refer to circled number(s) on the diagnostic chart.
1. Checks A/C request signal to VCM-A.
2. Checks compressor clutch and connections.
3. Checks CKT 150.
4. Determines which diagnostic path to take (part 1 or part 2).
5. Checks CKT 39 at relay.
6. Checks relay, CKT 459, VCM-A connections or VCM-A.

DIAGNOSTIC AIDS
Make sure that the correct A/C relay is installed on the vehicle.