Air Conditioning System Circuits

With the ignition switch in ON (I I), voltage is applied to the coil and contacts of the A/C compressor clutch relay through fuse 11. When you push the A/C switch ON, and the blower switch is in position LO, M1, M2, or MAX, a "ground" input is provided to the engine control module (ECM) through the A/C thermostat and the A/C pressure switch.


A/C Thermostat


The A/C thermostat is located on the evaporator housing. The A/C thermostat turns off the A/C compressor clutch if the temperature at the evaporator goes below .5 ± 1°C (33 ± 2°F). This prevents condensation from freezing on the evaporator fins and blocking the air delivery into the passenger compartment. The blower motor will keep running when the sensor turns off the compressor.


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. The switch will sense abnormally high or low pressure, and open the circuit. This removes ground, and the compressor will stop running.


Thermal Protector


The thermal protector is located on the A/C compressor. If this protector senses high temperature in the compressor, its switch will open, turning the compressor off Once the compressor cools, the switch will close and the compressor will begin running again.