PCM Controlled Air Conditioning

The air conditioning system uses a compressor with variable displacement. This compressor is referred to as the V-5 type compressor. The V-5 compressor meets A/C requirements without cycling. The A/C compressor operation is controlled by the powertrain Control Module (PCM) for the following reasons:
^ Improved idle quality during compressor clutch engagement
^ Improved wide open Throttle Performance (WOT)
^ Protects the A/C compressor from operation with incorrect refrigerant pressures

The A/C clutch electrical system consists of the following components:
^ The A/C control head and/or the A/C programmer
^ The A/C refrigerant pressure sensor
^ The A/C compressor clutch
^ The A/C compressor clutch relay
^ The PCM

When an A/C mode is selected at the A/C control head, the A/C programmer provides a 12 volt signal to the A/C request circuit. The PCM monitors the A/C request circuit and controls the A/C compressor relay based on the A/C request signal. This allows the PCM to increase the engine idle speed just prior to A/C clutch engagement for better idle quality. In addition, the PCM will command the cooling fans ON during A/C operation. The PCM also monitors the A/C refrigerant pressure sensor circuit. If the A/C refrigerant pressure is too high or low, the PCM will disable the A/C compressor relay.

The PCM will enable the A/C compressor clutch whenever the engine is running and the A/C has been requested unless one or more of the following conditions are present:
^ The throttle angle is more than 96 percent.
^ The A/C head pressure is more than 440 psi (4.6 volts) or less than 35 psi (0.4 volt) as determined by the A/C refrigerant pressure sensor.
^ The ignition voltage is less than 10.5 volts.
^ The engine speed is more than 4400 RPM for any amount of time.
^ The engine speed is more than 3700 RPM for more than 5 seconds.
^ The Engine Coolant Temperature (ECT) is more than 124°C (255°F).
^ The Intake Air Temperature (IAT) is less than 5°C (41°F).

Any of the conditions described above will inhibit A/C compressor relay operation.