Evaporator Temperature Sensor / Switch: Description and Operation

The A/C thermostat senses evaporator temperature. With the evaporator temperature above 41 degrees F (5 degrees C), the switch closes to activate the A/C compressor clutch. With the evaporator temperature below 33 degrees F (less than 1 degree C), the A/C thermostat opens. In this way, the evaporator temperature stays above 32 degrees F (0 degrees C) and moisture on the evaporator tins will not freeze and block air flow.