Inside and Ambient Air Temperature Sensors
WARNING: This page is about a different car, the 2008 Buick LaCrosse and 2008 Buick Allure. However, it is still accessible from the selected car via links, so may be relevant.
The HVAC control module supplies the inside and ambient air temperature sensors with a low reference circuit and 5-volt signal circuit. The inside air temperature sensor has a fan motor that operates using body ground and a 12 volt supply from the HVAC control module when the ignition and HVAC control module are ON. The HVAC control module determines the voltage drop across the sensors, which is proportional to temperature. As the air temperature increases, the sensor resistance decreases and the voltage signal decreases. As the air temperature decreases, the sensor resistance increases and the voltage signal increases.