Manual A/C-Heater Systems: Operation: Thermistor

If evaporative temperature of refrigerant drops to 32°F (0°C) or less, the evaporator fins develop frost or ice. This reduces evaporator core airflow, lowering cooling capacity. A thermistor, installed on the evaporator, prevents this frost or ice from forming by temporarily opening compressor clutch circuit. Ice is allowed to melt and be drained away as water. After ice is melted, compressor clutch is reengaged.