VCM Charts

A/C Clutch Control Diagnosis:

A/C Clutch Control Diagnosis:

A/C Clutch Control Circuit:

Circuit Description
When the A/C control switch is turned "ON," voltage is supplied to the 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 259, 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 (pg1 or pg2).

5. Checks CKT 50 at relay.

6. Checks relay, CKT 259, VCM connections or VCM.

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

1. Checks for voltage at relay.

2. Checks CKT 248 and the relay.

3. Checks CKT 66.

4. Checks CKT 59 and high pressure switch.

5. Checks state of charge CKT 901 and low pressure switch.

Diagnostic Aids
Make sure that the correct A/C relay is installed on the vehicle.