I have read many times on this very same forum that if one wants to stay cool while traveling down the highway in a very warm state like Arizona, where the op is from, that one has to run the over head air. To me, when the outside air is 100 degrees and the inside air is 75 or 80 degrees, that is still hot!!! Most motorhomes are not well known for their insulation quality. No matter how much cold air your AC blows, there are a lot of cubic feet that it is trying to cool down, and mother natures is doing everything she can to prevent it!