Component Tests and General Diagnostics

CHART C-10
AIR CONDITIONING (A/C) CLUTCH CONTROL CIRCUIT DIAGNOSIS

Circuit Description:
The A/C clutch control relay is Engine Control Module (ECM) controlled to delay A/C clutch engagement about .4 second after A/C is turned "ON". This allows the Idle air control to adjust engine rpm before the A/C clutch engages. The ECM also causes the relay to disengage the A/C clutch during Wide Open Throttle (WOT), when high power steering pressure is present, or if engine is overheating. The A/C clutch control relay is energized when the ECM provides a ground path for CKT A2.
The dual pressure switch (located in the receiver/dryer) will open if A/C pressure is less than 40 psi (276 kPa) or if A/C pressure exceeds 440 psi (3034 kPa).
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 WOT.
- Smooths cycling of the compressor by providing additional fuel at the instant clutch is applied.
Turning "ON" air conditioning supplies CKT B8 battery voltage to the clutch control relay and terminal "B8" of the ECM connector. After a time delay of about 1/2 second the ECM will ground terminal "A2" of the ECM connector, CKT A2, and close the control relay. A/C compressor clutch will engage.

Test Description:
Number(s) refer to circled number(s) on the diagnostic chart.
1. Checks for low refrigerant or dual pressure switch as cause for no A/C.
2. This and following tests check for faulty A/C control relay.
3. This and following tests check for open ECM wiring or faulty ECM.




CHART C-10
AIR CONDITIONING (A/C) CLUTCH CONTROL CIRCUIT DIAGNOSIS
"AFTER REPAIRS," REFER TO DIAGNOSTIC TROUBLE CODE (DTC) CRITERIA AND CONFIRM DTC DOES NOT RESET.