Chart C-10 A/C Clutch Control Circuit Diagnosis

Chart C-10:

CHART 1 OF 2

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

CHART 2 OF 2

A/C Circuit:

CIRCUIT DESCRIPTION:
The A/C clutch control relay is energized when the ECM provides a ground path through CKT 459 and A/C is requested. A/C clutch is delayed about .3 seconds after A/C is requested. This will allow the IAC to adjust engine rpm for the additional load. The ECM will temporarily disengage the A/C clutch relay for calibrated times for one or more of the following conditions:

^ Hot engine restart.
^ Wide Open Throttle (WOT) (TPS over 99% disable).
^ Engine speed greater than about 6000 rpm.
^ During IAC reset.

The A/C clutch relay will remain disengaged when a DTC 66 is present, if pressure is out of range or there is no A/C request signal, due to an open A/C select switch or circuit.

TEST DESCRIPTION: The 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. Determines if the signal is reaching the ECM through CKT 66 from the A/C control panel. Signal should only be present when an A/C mode or defrost mode has been selected.
3. Be sure to consider branch circuits and splices to other components particularly if the HTR-A/C fuse is blown causing multiple open circuits.
4. Determines if the pressure transducer is out of range causing the compressor clutch to be disengaged.
5. With the engine stopped and field service mode activated, the ECM should be grounding CKT 459, which should cause the test light to be "ON."
6. Be sure to consider branch circuits and splices to other components, particularly if the gauges fuse is blown causing an open CKT 39.


DIAGNOSTIC AIDS:
If complaint is insufficient cooling, the problem may be caused by an inoperative cooling fan. For cooling fan diagnosis, See Chart C-12, Coolant Fan Control Circuit. A/C pressure outside of a range of 41 to 426 psi will cause the compressor to be disabled by the ECM. Observe "SCAN" tool A/C pressure for 2 minutes with engine idling and A/C "ON." Scan pressure should be within 20 psi of actual. If not, check for a circuit problem using DTC 66 chart or replace the A/C pressure sensor. Powertrain Controls - ECM/PCM