In order to improve engine operation, and protect the A/C
compressor and A/C clutch during Wide Open Throttle (WOT) performance, the
A/C compressor operation is controlled by the PCM.
This A/C system consists of the following components:
| • | The heater and A/C control |
| • | The A/C Evaporator Sensor |
| • | The A/C refrigerant pressure sensor |
| • | The A/C compressor clutch |
When the HVAC control assembly is placed in the A/C mode, a request
signal is sent to the PCM. The PCM will then energize the A/C clutch relay,
unless abnormally high or low A/C pressure is detected by the A/C refrigerant
pressure sensor. The PCM also monitors the A/C evaporator temperature sensor
to cycle the A/C clutch. If the PCM detects an A/C temperature less than 2°C
(36°F), the A/C clutch will be prohibited from being enabled. The PCM
will also turn the cooling fans ON when A/C is requested. The A/C clutch relay
is controlled by the PCM so that the PCM can increase idle speed before turning
ON the clutch or disable the clutch during WOT, or high coolant temperature.
The PCM will energize the A/C clutch whenever the engine
is running less than 4100 RPM and A/C has been requested, unless any
of the following conditions are met:
| • | Wide Open Throttle (WOT). |
| • | A/C head pressure greater than 414 psi or less than 0 psi
(as determined by the A/C refrigerant pressure sensor). |
| • | A/C Evaporator temperature less than 2°C (36°F) |
| • | Ignition voltage less than 10.5 volts. |
| • | Engine speed greater than 5250 RPM for 180 seconds. |
| • | ECT greater than 125°C (257°F). |
The A/C Request Table should be used for diagnosing the A/C request
circuit only. Refer to Section 1B of the appropriate service manual should
be used for diagnosing the refrigerant portion of the system.
The scan tool will be used in diagnosing the system. The PCM has the
ability to display the following parameters:
| • | A/C request input to the PCM |
| • | A/C Evaporator temperature |
| • | A/C clutch ON or OFF status |
Refer to Heater Ventilation and Air Conditioning (HVAC)
for service procedures.
