Evaporator Temperature Sensor
WARNING: This page is about a different car, the 2002 Pontiac Montana, 2002 Oldsmobile Silhouette, and 2002 Chevrolet Venture. However, it is still accessible from the selected car via links, so may be relevant.
The A/C system is protected by the evaporator temperature sensor. This sensor is mounted on the evaporator core and provides the HVAC control module with the surface temperature of the evaporator core. If the evaporator temperature sensor reads a temperature of 0°C (32°F), the HVAC control module will turn off the A/C compressor clutch until evaporator temperatures reach 2°C (36°F).
The HVAC control module sends out a 5 volt reference signal to the evaporator temperature sensor over the 5 volt reference circuit. A thermistor varies the reference voltage back to the HVAC control module through the low reference circuit.