The air conditioning system uses a compressor with variable
displacement.
The A/C compressor clutch is controlled by the PCM. The HVAC controller
sends the A/C request through the Class 2 serial data circuit to the
PCM. This allows the PCM to manage idle quality, improve wide open throttle
(WOT) performance, and to protect the A/C system from excessively high
and low pressures.
The PCM controlled air conditioning system uses a variable displacement
compressor. The compressor meets the A/C requirements without cycling. For
a description of the system and an explanation of the components used,
refer to
Dual Zone Air Conditioning (A/C) System Description
in HVAC.
The A/C electrical system consists of the following components:
| • | A/C refrigerant pressure switch |
| • | A/C compressor clutch relay |
| • | Class 2 serial data circuit |
When A/C is selected through the A/C control head a signal
is communicated via class 2 to 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 more than 90 percent |
| • | A/C head pressure more 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 more than 6900 RPM for 5 seconds |
| • | ECT more than 121°C (250°F) |
| • | IAT less than 0°C (32°F) |
The
Powertrain Control Module Controlled Air Conditioning (A/C) 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, the
VDOT Air Conditioning (A/C) System Diagnosis
in HVAC should be used.
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.
