Chart C-10, 2.5L, A/C Clutch CTRL CKT Diagnosis: Notes

When A/C mode is selected, battery voltage is supplied to compressor low pressure switch. If A/C refrigerant pressure is sufficient, low pressure switch will be closed and complete circuit to closed high pressure switch and to circuits No. 67 and 459. Voltage on circuit No. 459 is shown by Tech 1 scan tester as A/C request YES (voltage present) or NO (no voltage). When A/C request is sensed by ECM, ECM will ground circuit No. 458 of A/C clutch relay. A/C clutch relay contacts will close and current flows from circuit No. 459 to circuit No. 59 to engage A/C compressor clutch. Tech 1 scan tester shows grounding of circuit No. 458 as A/C clutch ON. When voltage is sensed by ECM on circuit No. 67, cooling fan is turned on.

1. ECM will energize A/C relay only when engine is running. This test determines if relay or circuit No. 458 is faulty.
2. Low pressure and high pressure switches must be closed so A/C request (12 volts) will be present at ECM.
3. Short to ground in any part of A/C request or A/C clutch control circuits may cause a blown fuse.
4. With engine idling and A/C on, ECM should ground circuit No. 458, causing test light to glow.
5. Determines if signal is reaching low pressure switch on circuit No. 66 from A/C control panel. Signal should only be present when A/C mode or defrost mode has been selected.