GM Service Manual Online
For 1990-2009 cars only

The following sensors affect the automatic control of the in-vehicle temperature.

    • An in-vehicle sensor
    • An outside air sensor

Both of the sensors are temperature-sensitive thermisters. The resistance of the sensors varies inversely to the temperature. The resistance value determines level of the signal that is sent to the heater-A/C control. The heater-A/C control microprocessor uses this information in order to develop command signals for the following components:

    • The vacuum solenoid module
    • The temperature motor actuator
    • The blower motor pulse width module

A hose duct connects the in-vehicle sensor housing to an aspirator. Air flow from the HVAC module creates a slight vacuum at the aspirator end of the hose. This vacuum completes the following functions:

    • Draws in-vehicle air over the in-vehicle sensor
    • Improves the accuracy of the cabin temperature that is predicted by the sensor