Component Diagnostic Charts/Tests

Chart C-10 - A/C Clutch Control:

Wiring Diagram for A/C Clutch Control:

CHART C-10 A/C CLUTCH CONTROL DIAGNOSIS


Circuit Description:

ECM control of the A/C Clutch improves idle quality and performance by;

Delaying Clutch apply until the idle air rate is increased.
Releasing clutch when idle speed is too low.
Releasing clutch at wide open throttle.
Smooths cycling of the compressor by providing additional fuel at the instant clutch is applied.

Voltage is supplied to the A/C Clutch Control relay on CKT 50 when the A/C power relay is energized by the A/C Control Switch. Also, when the A/C is turned "ON", voltage is supplied to the A/C relay coil on CKT 67 through the closed pressure cycling switch. This same voltage is supplied as a signal to ECM pin B8. After a time delay of about 1/2 second the ECM will ground terminal "C2", CKT 458, and close the A/C relay contacts.

When relay is energized battery voltage from CKT 50 is supplied to the A/C clutch through the relay and CKT 59.


Test Description: Numbers below refer to circled numbers on the diagnostic chart.

1. The ECM will only energize the A/C relay, when the engine is running. This test will determine if the relay, or CKT 459, is faulty.

2. In order for the clutch to properly be engaged, the low pressure switch must be closed to provide 12 volts to the relay, and the high pressure switch must be closed, so the A/C request (12 volts) will be present at the ECM.

3. Determines if the signal is reaching the ECM on CKT 366 from the A/C control panel. Signal should only be present when the A/C mode or defrost mode has been selected.


4. A short to ground in any part of the A/C request circuit, CKT 67 to the relay, CKT 902 to the A/C clutch, or the A/C clutch, could be the cause of the blown fuse.

5. With the engine idling and A/C "ON", the ECM should be grounding CKT 459, which should cause the test light to be "ON".

Diagnostic Aids:

If complaint was insufficient cooling, the problem may be caused by an inoperative cooling fan. The engine cooling fan should turn "ON", when A/C is "ON".