Evaporator Temperature Sensor / Switch: Description and Operation
EVAPORATOR THERMISTORWhen the evaporative temperature of a refrigerant drops toss to 2.5 °C (36.5 °F) or below, the evaporator fins get stuck with frost or ice, reducing the airflow, lowering the cooling capacity. The thermistor is a sensor which is used to prevent this frosting or icing.
The thermistor installed to evaporator converts the evaporative temperature into a resistance value and send it to A/C amplifier.