Ok I'm cruising down the interstate, with the AC on. Slowly but surely, after a bit, it starts to blow less and less, while getting colder and colder. Finally it quits blowing at all, so I have to turn the heat on, where it slowly unthaws it until it's blowing full blast again. But I found that if I keep the AC on max, and a few notches above full cold, that it usually won't freeze up. Is this a problem with my AC system, or just the blower motor??