Inside Air Temperature Sensor Assembly

WARNING: This page does not describe the selected car, but rather 7 other vehicles, including the 2002 GMC Yukon XL, 2002 GMC Yukon, 2002 Chevrolet Tahoe, 2002 Chevrolet Suburban, and 2002 Chevrolet Avalanche. However, it is still accessible from the selected car via links, so may be relevant.

The HVAC control module receives an input of the passenger compartment air temperature from the inside air temperature sensor assembly. A fan located internally to the inside air temperature sensor assembly housing continually draws passenger compartment air over the sensor.

The inside air temperature sensor is a Negative Temperature Coefficient (NTC) thermistor, when the temperature of the sensor changes so does the resistance across the thermistor. When the air temperature is warm, the sensor resistance and signal voltage is low. When the air temperature is cool, the sensor resistance and signal voltage is high. Inside the HVAC control module 5 volts is supplied to the inside air temperature signal circuit through a fixed resistance. The fixed resistance inside the HVAC control module makes the signal circuit a series circuit. As the resistance of the sensor changes, the amount of voltage it drops also changes since it is in series with the fixed resistance inside the HVAC control module. The HVAC control module monitors the voltage drop of the circuit which is needed to calculate the air temperature. The ground for the inside air temperature sensor is provided by the low reference circuit.

The HVAC control module will use a default value for the inside air temperature signal if there is a fault with the input. This value will be displayed on the scan tool. The HVAC control module will use this default to ensure HVAC operation is still performed.