C-10 ~ Air Conditioning Clutch Control

Chart C-10 Wiring Diagram:

Chart C-10 - A/C Clutch Control Diagnosis:

CIRCUIT DESCRIPTION:
The A/C clutch control relay is ECM controlled to delay A/C clutch engagement about .4 seconds after A/C is turned "ON." This allows the IAC 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), if engine is overheating or if the P/S pressure switch is closed.

The A/C clutch control relay is energized, when the ECM provides a ground path for CKT A2. The low pressure switch will open if A/C pressure is less than 40 psi (276 kPa). The high pressure switch will open, if A/C pressure exceeds about 440 psi (3034 kPa).

ECM control of the A/C clutch improves idle quality and performance by:
- Delaying clutch engagement until idle speed is increased
- Disengages A/C clutch when idle speed is too low
- Disengages A/C clutch when at WOT
- Smooths cycling of compressor by providing additional fuel the instant clutch is applied.

Turning ON A/C 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 seconds, the ECM grounds terminal "A2" of the ECM connector, CKT A@, and close the control relay. A/C compressor clutch engages.

TEST DESCRIPTION
Numbers below refer to circled numbers on the diagnostic chart.
1. Checks for low refrigerant or faulty 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 faulty wiring or ECM.