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


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 or during high power steering loads.
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 59 by the A/C Control 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 "A2", CKT 905, and close the A/C relay contacts.

When relay is energized battery voltage from CKT 59 is supplied to the A/C clutch through the relay and CKT 959.


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 905, is faulty.

2. In order for the clutch to properly be engaged, the pressure cycling 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 59 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 59, CKT 959 to the A/C clutch, or the A/C clutch, could be the cause of the blown fuse.

5. With the ignition "ON" and the diagnostic terminal grounded, the ECM should be grounding CKT 905 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" and A/C head pressure exceeds about 233 psi. If not, see CHART C-12 for diagnosing the cooling fan.