Evaporator Temperature Sensor / Switch: Description and Operation

The evaporator temperature sensor is a two-wire temperature sensing element located at the coldest point on the face of the evaporator. The sensor is attached to the evaporator coil fins. The evaporator temperature sensor prevents condensation on the evaporator coil from freezing and obstructing A/C system air flow.

The evaporator temperature sensor monitors the temperature of the A/C evaporator. The sensor will change its internal resistance in response to the temperatures it monitors. The A/C-heater control is connected to the sensor through a sensor ground circuit and a sensor signal circuit. As the evaporator temperature increases, the resistance of the sensor decreases and the voltage monitored by the A/C-heater control decreases. The A/C-heater control uses this monitored voltage reading to an indication of the evaporator temperature. The A/C-heater control is programmed to respond to this input by cycling the A/C compressor clutch as necessary to optimize A/C system performance and to protect the A/C system from evaporator freezing. The external location of the sensor allows the sensor to be removed or installed without disturbing the refrigerant in the A/C system.

The evaporator temperature sensor is diagnosed by performing the ATC Function Test using a DRBIII(R) scan tool. Refer to Body Diagnostic Procedures.

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