Operation
The air conditioning system uses a variable displacement compressor
referred to as type V-5. 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. |
When an A/C mode is selected, the A/C control head/programmer sends
the A/C request signal to the PCM. The A/C compressor clutch relay is controlled
by the PCM. The PCM provides a ground path for the A/C relay coil. The PCM
will enable the A/C compressor clutch relay whenever the engine is running
and the A/C has been requested by the A/C control head/programmer. When the
A/C compressor relay is engaged, battery voltage is supplied to the compressor
clutch coil. The PCM and the A/C control head/programmer monitor the A/C pressure
sensor signal. If the A/C pressure sensor signal indicates an A/C pressure
outside the normal operation range, the A/C control head/programmer will remove
the A/C request signal from the PCM. The PCM will disengage the A/C relay.
The PCM will enable the A/C relay 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 35 psi (0.4 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 4300 RPM for longer than 1 seconds. |
| • | 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.
Diagnosis
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 diagnoses the electrical
portion of the A/C compressor clutch circuit. 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 displays the A/C request and refrigerant pressure inputs to the PCM.
The scan tool displays the PCM commanded state of the A/C clutch. The scan
tool can override the A/C request signal and energize the A/C control relay.
