Component Diagnostic Charts/Tests

Chart C-10:

Wiring Diagram For A/C Clutch Control:

CIRCUIT DESCRIPTION:

The A/C clutch control relay is controlled by the ECM to delay clutch engagement for approximately .4 seconds after the A/C system is powered. This allows the Idle Air Control (IAC) to adjust engine speed before the A/C clutch engages. The ECM controls the relay to allow the clutch to disengage during Wide Open Throttle (WOT), high power steering pressure present, or if the engine is overheating. The A/C clutch control relay is energized when the ECM provides a ground path for circuit 459. The low pressure switch will open if A/C pressure is below 40 psi (276 kPa), and the high pressure switch opens at approximately 440 psi (3034 kPa).


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

1. The ECM will energize the A/C relay only when the engine is running. This test will determine if the relay or circuit 459 is faulty.
2. In order for the clutch to be engaged, the low and high pressure switches must be closed so the A/C request (12 volts) will be present at the ECM.
3. This determines if the signal is reaching the ECM on circuit 604 from the A/C control panel. The signal should be present when the A/C or defrost modes has been selected.
4. A short to ground in any part of the A/C request, circuit 604, circuit 59 to the A/C clutch, or clutch control circuit may be the cause of a blown fuse.
5. With the engine idling and the A/C energized, the ECM should be grounding circuit 459. This should cause the test light to illuminate.


DIAGNOSTIC AIDS:

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