For 1990-2009 cars

The air conditioning system uses a compressor with variable displacement.

The A/C compressor clutch is controlled by the PCM. The HVAC controller sends the A/C request to the BFC and the BFC sends this signal through the Class II serial data circuit to the PCM. This allows the PCM to manage idle quality, improve wide open throttle performance, and to protect the A/C system from excessively high and low pressures.

The PCM controlled air conditioning system uses a variable displacement compressor. The compressor meets the A/C requirements without cycling. For a description of the system and an explanation of the components used, refer to HVAC Compressor Controls Circuit Description in HVAC Systems - Manual.

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 427 psi (4.27 volts) or less than 41 psi (0.35 volt) (as determined by the A/C refrigerant pressure sensor).

• | Ignition voltage below 9.5 volts.

• | Engine speed greater than 6900 RPM for 5 seconds.

• | ECT greater than 121°C (250°F).

• | IAT less than 0°C (32°F)

The A/C Compressor Control Circuit Diagnosis should be used for diagnosing the electrical portion of the A/C compressor clutch circuit. When diagnosing the refrigerant portion of the HVAC system, the Functional Check in HVAC, should be used.

A scan tool will be used in diagnosing the system. The scan tool has the ability to read the A/C request and refrigerant pressure inputs to the PCM. The scan tool can display when the PCM has commanded the A/C clutch on. The scan tool should have the ability to override the A/C request signal and energize the A/C control relay.