I get heat on one side and not the other. Only cold air comes out of the defroster. My guess is some sort of vacuum control is involved. any ideas what i will need for parts?

If you have auto climate control (and I believe you do), it sounds like an actuator may be defective. I have to consult the service manual to be sure but the climate control assy (behind the glovebox) has actuators and vacuum solenoids that control the system. I have seen the whole assy available on ebay (can't remember the price - $140?) but the actuators you may have to get from a boneyard (bonneville, Lesabre, 98 & Park av all have em). I don't know about dealer but you can check GMpartsdirect for a cheaper price. There are some checks you can do before you go and replace parts. Do you have access to a service manual? If not, let me know as I have '96 & "99 manuals (the system is pretty much the same from 96 to 99).