Why does my passenger side AC blow hot air no matter how low the temp is set? on 2005 Hummer H2

Our H2 has air conditioning w/tri-zone climate controls, but the front passenger side only blows hot air. I can't seem to figure his out? I want to try and have an idea of what it might be before I take it to get fixed.

Asked by for the 2005 Hummer H2
its mostly a blend door problem, they cost approx 275.00 each and are easy to change except one. the hard one takes about 5 hrs. i think you are looking at an easy one though for your problem