For 1990-2009 cars

### General 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:

• | Improves idle quality during compressor clutch engagement.

• | Improves wide open throttle performance (WOT).

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

For a description of the system and an explanation of the components used, refer to Heating and Air Conditioning of the service manual.

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).

### Diagnosis

When diagnosing the refrigerant portion of the HVAC system.

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 has the ability to override the A/C request signal and energize the A/C control relay.