A/C Compressor Controls

The A/C ON input at cavity (A3) of the fan control unit is grounded through the A/C triple pressure switch, and the heater control panel at G303. The fan control unit supplies two input signals to the powertrain control module (PCM), indicating that the A/C system has been turned on, and that the engine idle speed must be increased.


The fan control unit and powertrain control module (PCM) are grounded from their (PDSW) terminals, through the middle pressure switch in the A/C triple pressure switch to G153.


When the ignition switch is in RUN, the powertrain control module (PCM) provides a ground for the A/C compressor clutch relay, energizing it. The A/C compressor clutch is energized by fuse 3, and the closed contacts of the A/C compressor clutch relay.


The fan control unit uses the radiator fan control sensor to measure the engine's coolant temperature:


^ When the radiator's coolant temperature is above 84°C (183°F), both the condenser and radiator fans will run at low speed.


^ When the radiator's coolant temperature is above 90°C (194°F), the fan control unit will cause both fans to run at full speed.


^ When the radiator's temperature exceeds 109°C (268°F),the fan control unit, through the powertrain control module (PCM) deenergizes the A/C compressor clutch relay and the A/C compressor clutch.


When refrigerant pressure becomes too high (due to blockage), or too low (due to leakage),the A/C triple pressure switch will open. This prevents the A/C compressor clutch relay from energizing, which disengages the compressor clutch.


The radiator fan control sensor will disengage the air conditioning system if radiator coolant temperature exceeds 110°C (230°F).