One of the very common discussions on all these forums is people complaining that their fan is running and blowing cold air while their heat is on and the answer everyone gives is to set the fan on auto so you don't get the cold air. Now I do not know the entire set up but I have seen that topic hundreds of times. Many trips we do not open the windows and just run the fan without the AC. It keeps the trailer nice and cool so whatever it does, it works for us.