I have the same problem. There is no heat on the passengers side, it only blows out cold air. I took mine to a local GM dealer cuz theres not a Caddie dealer near me, and they said it was that the acuator was stuck so they went in and "unstuck" it. Well like 2 weeks later there was no hot air on the passengers side again so I went back and they said that I would have to buy a new one... which will cost me like $80. This probably dont help you out any but I thought I would just tell you.
Angel