Sunload Sensor
WARNING: This page is about a different car, the 2002 Buick Regal and 2002 Buick Century. However, it is still accessible from the selected car via links, so may be relevant.
The sunload sensor provides the HVAC control module software with the amount of sun light entering the vehicle through the windshield. A 5-volt reference signal is sent from the HVAC control module to the sunload sensor over the sunload sensor signal circuit. A variable photo-diode resistor inside the sensor varies the voltage. That varied voltage provides a signal to the software inside the HVAC control module. Remaining voltage from the sunload sensor is sent back to the HVAC control module ground through the low reference circuit.