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:

^ Improves idle quality during compressor clutch engagement.

^ Improves wide open throttle performance (WOT).

^ Provides A/C compressor protection from operation with incorrect refrigerant pressures.


The A/C electrical system consists of the following components:

^ A/C control head.

^ A/C refrigerant pressure sensor.

^ A/C compressor clutch.

^ A/C compressor clutch relay.

^ PCM.


Operation
When an A/C mode is selected at the A/C control head, the A/C control head provides a 12 volts 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 any of the following conditions are met:

^ Throttle greater than 90%.

^ A/C head pressure greater than 414 psi (4.27 volts) or less than 34 psi (0.35 volt) (as determined by the A/C refrigerant pressure sensor).

^ Ignition voltage below 10.5 volts.

^ Engine speed greater than 4500 rpm for 5 seconds or 5400 rpm.

^ ECT greater than 125°C (257°F).

^ IAT less than 5°C (41°F).