Evaporator Temperature Sensor / Switch: Description and Operation

SYSTEM OPERATION
The evaporator temperature probe prevents condensate water on the evaporator coil from freezing and obstructing A/C system air flow. It does this by cycling the compressor clutch on and off. The switch is attached to the evaporator coil with the sensing probe inserted into the coil fins.

The evaporator probe is a temperature sensing element located at the coldest point on the face of the evaporator. Output from the probe is sampled by the Body Control Module (BCM). It is used to switch the A/C compressor clutch OFF before evaporator freeze up occurs. The clutch is switched OFF when the probe temperature reaches 0.94° C (33.7° F). It is allowed to switch ON when the probe temperature reaches 2.05° C (35.7° F).

The evaporator probe is located on the lower right side of the evaporator housing.

A/C SWITCH/EVAPORATOR TEMPERATURE STATUS
When the ignition switch is in the "RUN" position, the Body Control Module (BCM) monitors the evaporator temperature and the status of the A/C switch. Based on this information, the BCM sends a CCD message to the Powertrain Control Module (PCM) indicating the A/C switch status and the evaporator temperature status.