How the System Works

The heater and A/C system controls the radiator fan, condenser fan, and A/C compressor clutch.

Battery voltage is supplied at all times through fuse 35 to the A/C compressor clutch relay (contacts). When the ignition switch is in its ON (II) position, battery voltage is supplied through fuse 13 to the A/C compressor clutch relay (coil), engine control module (ECM), condenser fan relay (coil), and the A/C thermostat switch to the open contacts of the A/C switch.

When you push in the A/C switch, and the blower switch is turned to the LO, M1, M2, or HI positions, the engine control module (ECM) receives an "A/C request" ON input.

The A/C compressor clutch relay is grounded by the engine control module (ECM). When energized, the A/C compressor clutch relay allows battery voltage to turn on the A/C compressor clutch.

When you press the A/C switch, the engine control module (ECM) is grounded through the A/C and blower switches. The A/C ON indicator light comes on when the A/C system is running.


A/C Thermostat


The A/C thermostat, located on the evaporator housing, turns off the A/C compressor clutch if the temperature at the evaporator falls below 1.5°C (350°F). This prevents condensation from freezing on the evaporator fins and blocking air delivery into the passenger compartment. The blower motor will continue running.


A/C Pressure Switch


The A/C pressure switch is located in the condenser outlet line where refrigerant is in a high temperature/high pressure liquid state. This switch senses abnormally high or low pressure in the refrigerant line and opens the circuit. This removes ground and turns off the compressor.


Thermal Protector


The thermal protector, located on the A/C compressor, opens and turns the compressor off if it senses high temperature. Once the compressor cools, the switch will close and the compressor will begin running again.