Component Diagnostic Charts/Tests

Chart C-10 - A/C Clutch Control Circuit Diagnosis:

Wiring Diagram For Chart C-10 - A/C Clutch Control Circuit Diagnosis:

A/C CLUTCH CONTROL CIRCUIT DIAGNOSIS (CHART C-10)


CIRCUIT DESCRIPTION:

The A/C clutch control relay is ECM controlled to delay A/C clutch engagement about 8 seconds after A/C is turned "ON." This allows the IAC to adjust engine rpm, before the A/C clutch engages. The ECM, also, causes the relay to disengage the A/C clutch during Wide Open Throttle (WOT), or if engine is overheating. The A/C clutch control relay is energized, when the ECM provides a ground path for CKT 459. The low pressure switch will open if A/C pressure is less than 40 psi (276 kPa). The high pressure switch will open, if A/C pressure exceeds about 440 psi (3034 kPa). The A/C pressure fan switch opens to turn the fan "ON," when A/C pressure exceeds about 200 psi (1380 kPa).


TEST DESCRIPTION: Numbers below refer to circled numbers on the diagnostic chart.

1. The ECM will only energize the A/C relay, when the engine is running. This test will determine if the relay or CKT 459 is faulty.

2. In order for the clutch to properly be engaged, the low pressure switch must be closed to provide 12 volts to the relay, and 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 CKT 67 from the A/C control panel. Signal should only be present when the A/C mode or defrost mode has been selected.

4. With the engine idling and A/C "ON," the ECM should be grounding CKT 459, which should cause the test light to be "ON."


DIAGNOSTIC AIDS:

If complaint was insufficient cooling, the problem may be caused by a inoperative cooling fan, or A/C pressure fan switch. The engine cooling fan should turn "ON," when A/C pressure exceeds a value to open the switch, which causes the ECM to energize the cooling fan relay. See CHART C-12, for cooling fan diagnosis.