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 SECTION 1B of the service manual.
The A/C electrical system consists of the following components:
| • | A/C refrigerant pressure switch |
| • | A/C compressor clutch relay |
When A/C is selected through the A/C control head a 12 volt
signal is supplied to the A/C request input of the PCM. The A/C compressor
clutch relay is controlled through the PCM. 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 monitors the A/C refrigerant pressure. If the A/C refrigerant pressure,
and engine operating conditions are within a specific calibrated acceptable
ranges the PCM will enable the A/C compressor relay. This is accomplished
by providing a ground path for the A/C relay coil within the PCM. When the
A/C compressor relay is enabled battery voltage is supplied to the compressor
clutch coil.
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 427 psi (4.27 volts)
or less than 41 psi (0.35 volt) (as determined by the A/C refrigerant
pressure sensor). |
| • | Ignition voltage below 9.5 volts. |
| • | Engine speed greater than 6900 RPM for 5 seconds. |
| • | ECT greater than 121°C (250°F). |
| • | IAT less than 0°C (32°F) |
A/C Clutch Circuit Diagnosis should be used for diagnosing
the electrical portion of the A/C compressor clutch circuit. When diagnosing
the refrigerant portion of the HVAC system, refer to SECTION 1B.
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 should have the ability to override the A/C request signal and
energize the A/C control relay.
