Chart C10 - A/C Clutch Control: Notes

The ECM control of the A/C clutch improves idle quality and performance by delaying clutch application about .4 second until idle air rate is increased. The ECM also causes the A/C clutch to release when idle speed is too low, during high power steering loads, during Wide Open Throttle (WOT) and during overheat conditions. The A/C clutch control relay is energized when the ECM provides a ground path for circuit No. 459. The low pressure switch will open if A/C pressure is less than 40 psi (2.8 kg/cm² ). The high temperature switch will open if A/C pressure exceeds about 440 psi (31 kg/cm² ). The A/C pressure fan switch opens when A/C pressure exceeds about 200 psi (14 kg/cm² ). A/C clutch should engage only if engine is running.

1. The ECM will only energize the A/C relay when the engine is running. This test will determine if the relay or circuit No. 459 is faulty.
2. In order for the clutch to properly be engaged, the pressure cycling switch must be closed to provide 12 volts to the relay. Also, the high pressure switch must be closed so the A/C request (12 volts) will be present at the ECM.
3. Determines if the signal is reaching the ECM on circuit No. 366 from the A/C control panel. Signal should only be present when the A/C mode or defrost mode has been selected.
4. A short to ground in any part of the A/C request circuit, circuit No. 67 to the relay, circuit No. 59 to the A/C clutch relay, or the A/C clutch could be the cause of the blown fuse.
5. If the ECM is seeing a high power steering pressure signal, the A/C clutch will be disengaged by the ECM.
6. With the engine idling and A/C on, the ECM should be grounding circuit No. 459, which should cause the test light to be on.