Theory Of Operation

The HVAC Module monitors the Sun (Solar) Sensors to calculate the sun load being subjected to the vehicle interior. The BCM monitors the Twilight Sensor to detect the ambient light conditions.

Sun Sensors:  Most Sun Sensors are the photodiode type, which provide increased resistance as the light intensity increases, so the signal from the sensor drops as the sun shines brighter. The operating range is between 0 and 5 volts. As the sun load increases, the voltage decreases. The signal is sent to the HVAC Module to adjust blend doors and fan speed. Bright sunlight conditions can result in the fan speed increasing, and blend doors opening to improve cooling. Sun Sensors do not respond to fluorescent light, which is read as darkness.

Twilight Sensor:  This sensor uses a photoelectric cell to determine the ambient lighting conditions so the BCM can determine when the headlights should be turned on or off. A photocell generates electricity when it is subjected to light. The Twilight Sensor can detect solar lighting as well as florescent lighting. This allows the BCM to turn the headlights on when traveling through a tunnel or parking garage with low lighting conditions.