Chart C-10 A/C Clutch Control Circuit Diagnosis

Chart C-10 Part 1 Of 2:

Chart C-10 Part 2 Of 2:

A/C Refrigerant Pressure Sensor:

CIRCUIT DESCRIPTION
The A/C compressor clutch control relay is energized when the Powertrain Control Module (PCM) provides a ground path through circuit 459 and A/C is requested. A/C compressor clutch is delayed about 0.3 seconds after A/C is requested. This will allow the Idle Air Control (IAC) to adjust engine RPM for the additional load. The A/C compressor clutch control relay will remain disengaged if pressure is out of range, or there is no A/C request signal due to an open A/C select switch or circuit.

The PCM will disable the A/C compressor clutch for any of the following reasons:
^ Engine not running.
^ Diagnostic Trouble Code (DTC) 66 or 70 is set and fault is current.
^ Engine Coolant Temperature (ECT) is about 124° C (255° F) or greater.
^ A/C refrigerant pressure is about 429 psi or greater.
^ A/C refrigerant pressure is about 38 psi or less.

If the PCM temporarily disabled the A/C compressor clutch, the clutch will be enabled as follows:
^ DTCs are cleared from current status.
^ 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.

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

Part 1
1. The PCM will only energize the A/C relay when the engine is running. This test will determine if the relay or circuit 459 is faulty.
2. Determines if the signal is reaching the PCM through circuit 66 from the A/C control panel. Signal should only be present when an A/C mode or defrost mode has been selected.

Part 2
1. Determines if the A/C refrigerant pressure sensor is out of range causing the compressor clutch to be disengaged.
2. With the engine stopped and A/C relay output test activated, the PCM should be grounding circuit 459, which should cause the test light to be "ON."

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. For cooling fans diagnosis, refer to System Diagnosis/Procedures/ Diagnostic Charts/Chart C-12. 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 PCM. Observe Tech 1 (or equivalent) 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. Tech 1 pressure should be within 20 psi of actual. If not, check for a circuit problem using DTC 66 or 70. Refer to System Diagnosis/Procedures/ Diagnostic Charts/Code 66 Powertrain Controls - ECM/PCM, or Code 70. DTC 70
If checkouts are OK, replace A/C refrigerant pressure sensor.