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 (VCM) 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 248. After a calibrated delay time (approximately 20 sec.), the VCM will ground CKT 459, enabling the relay and applying voltage to CKT 901. 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 on CKT 59. This voltage signal allows the VCM to make idle, timing and fuel corrections for smother 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.
2. Checks compressor clutch and connections.
3. Checks CKT 150.
4. Determines which diagnostic path to take (pg 1 or pg 2).
5. Checks CKT 39 at relay.
6. Checks relay, CKT 459, VCM connections or VCM.

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