Operation
Using inputs to both the powertrain control module (PCM) and to the
heater and A/C programmer, the PCM controls the compressor clutch. The following
components are the inputs to the PCM:
| • | The heater and A/C programmer request for the compressor |
| • | The heater and A/C programmer's A/C possible flag |
The following components are the inputs to the heater and A/C programmer:
| • | The low refrigerant pressure switch |
| • | The high refrigerant pressure switch |
| • | The A/C high side temperature |
| • | The A/C low side temperature |
| • | The rear defogger switch (from the instrument panel cluster (IPC)) |
| • | The ambient air temperature |
The A/C fuse supplies battery voltage to the compressor clutch through
the A/C clutch relay that the PCM controls.
When the following inputs to the heater and A/C programmer are at the
indicated values, the heater and A/C programmer will signal the PCM that compressor
operation is possible:
| • | The climate control setting is not OFF or ECON. |
| • | The outside temperature is above 4°C (40°F). |
When the PCM receives the A/C Request signal via class 2 from the heater
and A/C programmer, the PCM energizes the A/C relay coil by grounding the
A/C relay control circuit. This closes the relay contacts and applies the
fused battery voltage to the A/C compressor clutch. The PCM enables the
compressor clutch whenever the engine is running and A/C is requested unless
one or more of the following conditions are present:
| • | System voltage is less than 8 volts. |
| • | A/C pressure sensor indicates a low or a high A/C pressure condition. |
| • | High power steering load. |
| • | Throttle angle is greater than 90 percent. |
| • | Ambient air temperature is less than 4°C (39°F). |
| • | Evaporator Core temperature is less than -2°C (28°F). |
| • | Engine coolant temperature is greater than 126°C (259°F). |
PCM DTC(s) P0560, P0562, P0563, and P1545 affect the A/C
operation. Refer to the appropriate DTC tables to diagnose any PCM set DTC(s.)
The HVAC system may contain DTCs that also affect the A/C operation. Refer
to
Diagnostic System Check
in HVAC
Systems - Automatic to diagnose any HVAC DTCs.
The PCM Controlled Air Conditioning table diagnoses the electrical portion
of the A/C compressor clutch circuit when no DTC is set. To diagnose the refrigerant
portion of the HVAC system, refer to
System Performance Test
in Heater, Ventilation, and Air Conditioning (HVAC). A
scan tool will be used in diagnosing the system. The scan tool has the
following functions to aid diagnosis:
| • | Displays the PCM commanded state of the A/C clutch. |
| • | Can override the A/C Request and energize the A/C relay. |
