If you look back in the threads far enough, you'll find my saga of my first bus, a 40 foot (non-slide) with 3 cruise airs and the country coach OTR system. Coming from Salt Lake City heading towards Las Vegas at mid day (late June), the outside temp was well over 110. My compressor seized on the CC OTR, so I fired the generator and turned on the three cruise airs. As Jon mentioned, cruise airs get their air intake from down low, front of the bus. So, while driving, I'm guessing that the road temp was in excess of 140 degrees in the desert. Within an hour, all three cruise airs shut down on thermal overload. I limped in to Vegas, putting ice cubes in wet towels and wiping ourselves down as we drove.
My current bus has Prevost bus air, and 4 roof airs. A recent trip to Arizona over July 4th weekend it was 105 outside. With the bus air going, my wife was wearing a jacket inside the coach. However, when parked in the 110 degree heat of Arizona, 4 roof tops barely kept up with the heat, basically running 24/7.
Just FYI.
Ray