Cabin Temperature Sensor / Switch: Description and Operation

Inside Air Temperature Sensor

The inside air temperature sensor is also a thermistor. It is mounted at the top of the instrument panel carrier, just to the right of the radio. The inside air temperature sensor fits within a short horizontal tube connected to an aspirator duct. The duct, in turn, leads to the air conditioning module, just to the right of the evaporator. Airflow from the blower tends to draw a continual stream of air through the aspirator duct and past the inside air temperature sensor. This forced flow of inside air over the thermistor provides a constantly updated inside air temperature signal to the microprocessor.

Resistance of the inside air temperature sensor thermistor varies from over 100,000 ohms at -40°C (-40°F) to less than 2,000 ohms at 35°C (95°F). The microprocessor supplies a 5-volt reference voltage to the inside air temperature sensor thermistor and measures the voltage drop in the sensor circuit to tell whether the temperature air valve position must be changed.