PCM Controlled Air Conditioning

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:
^ 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 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 96%.
^ A/C head pressure is greater than 440 psi (4.6 volts) or less than 32 psi (0.3 volt) as determined by the A/C refrigerant pressure sensor.
^ Ignition voltage is less than 10 volts.
^ Engine speed is greater than 4400 RPM for any amount of time.
^ ECT is greater than 124°C (255°F)
^ IAT is less than 5°C (41°F)

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

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

The PCM Controlled Air Conditioning 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). 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.