The passenger compartment air sensor is located in the control head of the HVAC module behind a small grille. In this position it is exposed to the air present in the passenger compartment. This provides a sample of the inside air temperature. The sensor is a thermistor used to control signal voltage at the heater and A/C control. The heater and A/C control supply a reference voltage, about 5 volts internally, to the sensor and measures the voltage drop in the circuit to obtain a temperature signal. This signal is an input that tells the heater and A/C control how much cooling or heating will be required to deliver to passenger compartment.

When inside air temperature is cold, thermistor resistance is high, therefore the heater and A/C control will receive a high signal voltage input. If the air temperature is hot, the thermistor resistance is low, the heater and A/C control will receive a low signal voltage input.

Inspect the aspirator tube connection to the automatic climate control head and the HVAC module.