My 90C4 has been giving me some hater control problems that I can't figure out. The center two dash vents and the passenger das vent occasionally put out hot air, even if I have the AC on. It is very uncomfortable! If I stop the car for a while, go back out and try again, it often will then work normally. Cold air comes out of the floor vents, as well as the drivers side dash vent.
Where do I start my investigation for trouble shooting?
Dave

 

I'd start with Roly Baldwin's article at http://www.porsche964.co.uk/technical/servos.htm and check to see if your servo arms are actually moving when you turn the temp dial from cold to hot.

Cheers,
David