A solar sensor is a light-sensitive photo-diode that monitors the heat load of the sun on the vehicle. The sensors are located on top of the instrument panel, on either side of the defroster grill where sunlight can reach the sensors. As sunlight intensity increases, the resistance of the sensor decreases. As sunlight intensity decreases, the resistance increases. The Instrument Panel Integration Module (IPM) compares the solar sensor reading to the in-vehicle temperature reading and then determines how much cooling is required to reach and maintain the desired SET temperature.