Chart C-10, A/C Control Diagnosis (A/T) (1 Of 2) 4.3L Turbo PFI
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ECM controls operation of A/C clutch to improve idle quality and performance by:
- Delaying A/C clutch application until idle air rate is increased.
- Releasing A/C clutch when idle speed is too low.
- Releasing A/C clutch at wide open throttle operation.
- Smooths cycling of compressor by providing additional fuel the instant A/C clutch is applied.
Turning on A/C supplies battery voltage to clutch relay (circuit No. 59) and ECM terminal BC9. After a time delay of .5 seconds, the ECM grounds terminal GF1 (circuit No. 459), and closes control relay. A/C compressor clutch then engages.
NOTE:
Test numbers refer to test numbers on diagnostic charts.
- Checks for low refrigerant as cause for no A/C.
- This step and the steps that follow checks for faulty A/C control relay. QUAD-DRIVER CHECK is located under COMPUTERIZED ENGINE CONTROLS.