For 1990-2009 cars

### Operation

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:

• | Throttle angle is greater than 90%.

• | A/C head pressure is 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 is less than 10.5 volts.

• | Engine speed is greater than 5400 RPM for any amount of time.

• | Engine speed is greater than 4500 RPM for longer than 5 seconds.

• | ECT is greater than 125°C (257°F).

• | IAT is less than 5°C (41°F).

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

### Diagnosis

DTC P0530, P0560, P1639, or P1641 can affect A/C operation. Refer to the DTC tables if any DTCs are set.

The A/C Clutch Control Circuit Diagnosis table should be used for diagnosing the electrical portion of the A/C compressor clutch circuit if a DTC is not set. To diagnose the refrigerant portion of the HVAC system, refer to the Heater, Ventilation, and Air Conditioning (HVAC) section. A scan tool will be used in diagnosing the system. The scan tool has the ability to display 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 also has the ability to override the A/C request signal and energize the A/C control relay.