Evaporator Temperature Sensor / Switch: Description and Operation

Evaporator Temperature Sensor:

The evaporator temperature sensor is a thermistor with a sensing probe that is inserted between the fins of the A/C evaporator at its coldest point. The evaporator temperature sensor prevents condensate water on the A/C evaporator from freezing and obstructing A/C system air flow. The sensor probe is filled with a special silicone-based thermal grease. Two terminals within a molded plastic connector receptacle on the sensor connect it to the vehicle electrical system through a wire lead and connector of the HVAC wire harness.

The evaporator temperature sensor is a thermistor that operates on a 5-volt reference signal sent out by the body control module (BCM). The evaporator temperature sensor connects to the BCM through a two wire lead and connector of the HVAC wire harness. The evaporator temperature sensor monitors the temperature of the A/C evaporator and changes its internal resistance in response to changes in the evaporator temperature. In turn, the change in the sensors internal resistance changes the reference signal voltage read by the BCM.

The BCM uses the reference signal voltage as an indication that conditions are correct to request A/C operation, should the operator (manually) or the A/C heater control (automatically) so desire this function. In turn, the BCM broadcasts the A/C request on the programmable communications interface (PCI) bus, where it is read and processed by the powertrain control module (PCM). The PCM will check engine coolant temperature and refrigerant pressure temperature before activating the A/C compressor clutch.

The evaporator temperature sensor is diagnosed using a DRBIII (R) scan tool.

The evaporator temperature sensor cannot be adjusted or repaired and, if faulty or damaged, it must be replaced.