PCM Controlled Air Conditioning

Using inputs to both the Powertrain Control Module (PCM) and to the heater and A/C programmer, the PCM controls the compressor clutch. The following components are the inputs to the PCM:
^ The heater and A/C programmer request for the compressor
^ The heater and A/C programmer's A/C possible flag

The following components are the inputs to the heater and A/C programmer:
^ The low refrigerant pressure switch
^ The high refrigerant pressure switch
^ The A/C high side temperature
^ The A/C low side temperature
^ The rear defogger switch (from the Instrument Panel Cluster (IPC))
^ The ambient air temperature
^ The vehicle speed
^ The system mode

The A/C fuse supplies battery voltage to the compressor clutch through the A/C clutch relay that the PCM controls.

When the following inputs to the heater and A/C programmer are at the indicated values, the heater and A/C programmer will signal the PCM that compressor operation is possible:
^ The climate control setting is not OFF or ECON.
^ The outside temperature is above 4°C (40°F).

When the PCM receives the A/C Request signal via class 2 from the heater and A/C programmer, the PCM energizes the A/C relay coil by grounding the A/C relay control circuit. This closes the relay contacts and applies the fused battery voltage to the A/C compressor clutch. The PCM enables the compressor clutch whenever the engine is running and A/C is requested unless one or more of the following conditions are present:
^ System voltage is less than 8 volts.
^ A/C pressure sensor indicates a low or a high A/C pressure condition.
^ High power steering load.
^ Throttle angle is greater than 90 percent.
^ Ambient air temperature is less than 4°C (39°F).
^ Evaporator Core temperature is less than -2°C (28°F).
^ Engine coolant temperature is greater than 126°C (259°F).

PCM DTC(s) P0560, P0562, P0563, and P1545 affect the A/C operation. Refer to the appropriate DTC tables to diagnose any PCM set DTC(s.) The HVAC system may contain DTCs that also affect the A/C operation. Refer to A Diagnostic System Check in Heating and Air Conditioning to diagnose any HVAC DTCs.

The PCM Controlled Air Conditioning table diagnoses the electrical portion of the A/C compressor clutch circuit when no DTC is set. To diagnose the refrigerant portion of the HVAC system, refer to System Performance Test in Heating and Air Conditioning (HVAC). A scan tool will be used in diagnosing the system. The scan tool has the following functions to aid diagnosis:
^ Displays the PCM commanded state of the A/C clutch.
^ Can override the A/C Request and energize the A/C relay.