PCM Controlled Air Conditioning

In order to improve engine operation, and protect the A/C compressor and A/C clutch during Wide Open Throttle (WOT) performance, the A/C compressor operation is controlled by the PCM.

This A/C system consists of the following components:
^ The heater and A/C control
^ The A/C refrigerant pressure sensor
^ The A/C clutch relay
^ The A/C compressor clutch
^ The PCM

When the heater and A/C control is placed in the A/C mode, a request signal is sent to the PCM. The PCM then energizes the A/C clutch relay, unless abnormally high or low A/C pressure is detected by the A/C refrigerant pressure sensor. The PCM also turns the cooling fans ON when A/C is requested. The A/C clutch relay is controlled by the PCM so that the PCM can increase idle speed before turning ON the A/C compressor clutch or disable the A/C compressor clutch during WOT, or high coolant temperature.

The PCM energizes the A/C clutch whenever the engine is running less than 3950 RPM and A/C has been requested. The PCM will not energize the A/C clutch whenever any of the following conditions are present:
^ Throttle Angle greater than 86 percent.
^ A/C head pressure greater than 414 psi or less than 0 psi (as determined by the A/C refrigerant pressure sensor). The PCM re-enables the A/C system when the A/C high side pressure is less than 249 psi.
^ Ignition voltage less than 10 Volts.
^ Engine speed greater than 4294 RPM.
^ ECT greater than 125°C (257°F). The PCM re-enables the A/C at 121°C (250°F).

The scan tool is used in diagnosing the A/C system. The PCM has the ability to display the following parameters:
^ A/C request input to the PCM
^ A/C compressor status
^ A/C system refrigerant pressure
^ A/C clutch ON or OFF status