I have a 2005 2500HD 6.0l 4x4. Recently it has started blowing hot air out of the passenger side while still blowing cold on driver's side. Sometimes it is hotter than other days. This morning it was 52 degrees but I still ran the a/c and again it was blowing hot air. Even crazier than that, I had left my truck at the airport for 3 days and when I cranked it up and turned up the a/c it started blowing out of the defrost vents instead of the regular vents. This has only happened once though. Any suggestions?