Chart C-10, A/C Control Diagnosis (A/T) (1 Of 2) 4.3L Turbo PFI

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.

1. Checks for low refrigerant as cause for no A/C.
2. This step and the steps that follow checks for faulty A/C control relay. QUAD-DRIVER CHECK is located under COMPUTERIZED ENGINE CONTROLS.

Fig 1: A/C Clutch Circuit Schematic (4.3L Turbo PFI)

Courtesy of GENERAL MOTORS CORP.

Fig 2: A/C Clutch Circuit Flow Chart, (4.3L Turbo PFI) (1 Of 2)

Courtesy of GENERAL MOTORS CORP.