Compressor Control Signal

DESCRIPTION
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.
^ The A/C refrigerant pressure sensor.
^ The A/C compressor clutch.
^ The A/C compressor clutch relay.
^ The PCM.

OPERATION
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 lust 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:

^ Throttle angle is greater than 90%.
^ A/C head pressure is greater than 427 psi (4.27 volts) or less than 41 psi (0.35 volt) as determined by the A/C refrigerant pressure sensor.
^ Ignition voltage is less than 9.5 volts.
^ Engine speed is greater than 6900 RPM for longer than 5 seconds.
^ ECT is greater than 121°C (250°F).
^ IAT is less than 0°C (32°F).

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