Chart C-10, A/C Control Diagnosis (A/T) 4.3L Turbo PFI: Notes
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, ECM grounds terminal GF1 (circuit No. 459), and closes control relay. A/C compressor clutch then engages.
NOTE:
Test numbers refer to numbers on diagnostic charts.
- Checks for low refrigerant as cause for no A/C.
- This step and steps that follow check for faulty A/C control relay. See QUAD DRIVER CHECK under COMPUTERIZED ENGINE CONTROLS .
- Checks for faulty cycling switch. Solenoids and relays are turned on and off by ECM, using "drivers". Each driver is a part of a group of 4, called quad-drivers. Failure of one driver can damage any other driver in set. Solenoid and relay coil resistance should be greater than 20 ohms.