[ssgharkness020147]

That sounds like a bad vacuum pump for sure. Only getting air out of the defrost is a tell tale sign. I have had two fail, both in the summer so I cannot say for sure that he would only get cold air. Seeing as how the temps contol is vacuum operated I would say that makes sense. On the other hand the blend door motor is electric. Have him pull the vacuum with a gauge and let me know how much he pulls.