Sunload Sensor

WARNING: This page is about a different car, the 2002 GMC Sierra, 2002 GMC Cab & Chassis Sierra, 2002 Chevrolet Silverado, and 2002 Chevrolet Cab & Chassis Silverado. However, it is still accessible from the selected car via links, so may be relevant.

The sunload sensor provides the HVAC module software with the amount of sun light entering the passenger compartment through the windshield. With this input the HVAC control module can adjust cooling requirements based on the amount of heat load that the sun is placing on the vehicle.

The sunload sensor is a photoconductive diode, meaning that it is sensitive to light. When the sensor is in direct sunlight the signal voltage is low. When the sensor is in dark conditions the signal voltage is high. Inside the HVAC control module 5 volts is supplied to the sunload sensor 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 sunload. The ground for the sunload sensor is provided by the low reference circuit.

The HVAC control module will use a default value for the sunload sensor 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. A resistance check of the sunload sensor should not be performed as it will damage the sensor.