there are 2 sensors, one for the actual direct sunlight reading and one by your left knee for the actual in cabin temprature reading and depending on what each one senses the climate does what it needs to do to keep the temp at the temp you have set

the cover over the top is probably there to make sure the sensors doesn't see direct sunlight, i left a thermometer in the van in direct sunlight during the summer and the temps showed 55 degrees c