Help 87300E Automatic Teperature Control Problems

Hi --

I just bought an 87300E with about 110K miles on it. I love the car and love reading the posts at this site. Also in an attempt to save funds I purchase most of my parts through Phil at Fastlane.

I would really appreciate any help you could give me with the following problem. When I set the pushbutton controler cabin temperature gauge to 70 degrees when it's 90 degrees outside I experice the following problems.
1. Sometimes everything works fine;
2. Sometimes when starting the car the system pumps cold air out of the center vents and heated air out of the side vents. (To fix this I have to set the temperature wheel to "min." and the system will eventually pump cold air out of all vents but will not maintain a temp. its works all A/C all the time or no A/C); and
3. Sometimes the system works fine and then, when a system change is required to maintain a set temperature, it will start pumping heated air out of the side vents and cold air out of the center vents.
After speaking to my mechanic he suggested that I check the internal cabin temperature sensor (I replaced it with a new one) and that I check the auxillary fan that pulls cabin air over the internal temperature sensor in the headliner courtesy light assembly. I did this -- all hoses were connected and the auxillary fan worked to pull a small amount of air over the sensor. I do not know if the fan works all the time, but it did when I checked it.
After replacing the sensor the system seemed to work a little better -- sometimes perfectly and pumping hot air out of the side vents a little less frequently. But the system still suffers from the same problem, just not as often.
Does this require that I purchase and install a new pushbutton controler unit? If so, can I safely purchase a rebuilt one from the "German Star" (as advertised in the Star) for $209? or should I buy a new one? or is there a less expensive solution to this problem?
I'm pretty handy but, I am no expert. I have successfully replaced the cruise contol amplifier; the rebuilt speedometer; and the fuel level sender myself. My mechanic has done the following: Replaced the overload protection relay; the fuel pump relay; the oxygen sensor; and the struts (Bilstein HD's are great); he has rebuilt the altenator; replaced the brake pads; changed all the fluids; replaced the rubber part of the brake lines; replaced the tranny hoses, the coolant hoses and replaced the rear differential bushings and the flex discs. I also had all the broken wires between the body and the driver's side rear door repaired.
Other than the A/C problem the car seems to eat/loose a lot of oil. It could be a head gasket or a stem seal problem. Or it could be from my using a thin synthetic oil [10w30]; I've now switched to 15w50 Mobile One. Any thoughts?

Thanks in advance for any help you can give me.
Marc87300E, MMCLaw@Bestweb.net