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 (WOT) performance |
| • | Protection of 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 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 a 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 too 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:
| • | The throttle angle is more than 96 percent. |
| • | The A/C head pressure is more than 440 psi (4.6 volts)
or less than 35 psi (0.4 volt) as determined by the A/C refrigerant
pressure sensor. |
| • | The ignition voltage is less than 10.5 volts. |
| • | The engine speed is more than 5400 RPM for any amount of
time. |
| • | The engine speed is more than 4300 RPM for more than 1 second. |
| • | The engine coolant temperature is more than 124°C (255°F). |
| • | The intake air temperature IAT is less than 5°C (41°F). |
Any of the conditions described above will inhibit the A/C compressor
relay operation.
Diagnosis
A DTC P0530, P0560, P1639, or P1641 can affect the 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 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 the
refrigerant pressure inputs to the PCM. The scan tool can display if 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.
