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Chart C-10:

A/C Circuit:

CIRCUIT DESCRIPTION:
The A/C compressor clutch control relay is energized when the Engine Control Module (ECM) provides a ground path through CKT 366 and A/C is requested. A/C compressor 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 disable the A/C compressor clutch for any of the following reasons:
^ Engine not running.
^ DTC 66 is set and fault is current.
^ Throttle position is about 99 percent or greater.
^ ECT is about 122°C (251°F) or greater.
^ During an IAC motor reset.
^ Engine RPM is greater than about 4224 RPM.
^ A/C refrigerant pressure is about 429 psi or greater.
^ A/C refrigerant pressure is about 38 psi or less.

If the ECM temporarily disabled the A/C compressor clutch, the clutch will be re-enabled as follows:
^ Throttle position drops below about 89 percent.
^ A/C refrigerant pressure drops below about 199 psi.
^ ECT drops below about 119°C (246°F).
^ A/C refrigerant pressure rises above about 47 psi.
^ Engine RPM drops below about 3850 RPM.
^ IAC motor reset is complete.

TEST DESCRIPTION: Number(s) below refer to circled number(s) 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 366 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.

DIAGNOSTIC AIDS:
Be sure to consider branch circuits and splices to other components. If complaint is insufficient cooling, the problem may be caused by an inoperative cooling fan. Chart C-12, Coolant Fan Control Circuit. If fan operates correctly, refer to Heating and Air Conditioning. A/C refrigerant pressure outside of a range of 38 to 429 psi will cause the compressor clutch to be disabled by the ECM. Observe scan tool A/C refrigerant pressure for 2 minutes with engine idling and A/C "ON." If refrigerant pressure goes out of range, refer to Heating and Air Conditioning to measure and diagnose. Scanned refrigerant pressure should be within 20 psi of actual. If not, check for a circuit problem using DTC 66 chart or replace the A/C refrigerant pressure sensor.