Ambient Temperature Sensor / Switch HVAC: Description and Operation

Outside Air Temperature Sensor

The outside air temperature sensor is mounted to the radiator center support, just below the hood latch. In this position, it is exposed to airflow through the grille before the air enters the radiator. This provides a sample of outside air temperature.

The outside air temperature sensor is a thermistor - a temperature-sensitive electrical resistor that increases its resistance with a decrease in temperature and decreases its resistance with an increase in temperature. Resistance varies from over 100,000 ohms at 40°C (-40°F) to less than 2,000 ohms at 35°C (95°F).

The control assembly microprocessor supplies a constant 5-volt reference voltage to the sensor thermistor and measures the voltage drop in the sensor circuit to obtain a temperature signal. This signal is input that tells the microprocessor how much cooling or heating will be required to deliver air at the desired temperature to the passenger compartment.