I'm having problems with my heater switch,,,, It would always blow air out on the defrost, no matter what i have selected..Also, i took the control apart and looked at it,,,, it looks as though there should be 5 terminals on the switch and there are only 3 terminals.

Is this why i get air only on defrost and nothing else. I've checked my connection under the hood to the manifold and heater control valve, and they all look in line; according to other threads that I've read.

Please advise and thanks for the help.

If you have vacuum at the switch then you will need a new switch. If you do not have vacuum at the switch, then you will need to trace the line to see if you have a break. Plenty of info here using the search feature.

Exact same thing happened to me. The heater was always on and blew out of the defrost ducts at the base of the windshield. Regardless of the settings.

Turns out a plastic clip broke and prevented the controls from working:

http://img10.exs.cx/img10/1540/control1.jpg

http://img10.exs.cx/img10/6610/control2.jpg

See that metal arch? The plastic clip holds the two halfs of that wheel together. In the middle of that wheel is a neat flat rubber disc with a "maze like" pattern that the vacuum selection uses. When the clip broke, it couldn't pull a vacuum; hence none working controls. I've got a nut/bolt/washer setup until I can get a new clip.

Anyone know if those clips are available?

This heat/AC control unit is used on many models of old GM's. They are in all the salvage yards I go to and can be pulled out with very little trouble. But, it is best if you go to a yard that lets you pull the parts. That way you get what you want. Good luck.

i have the same problem.....can you just buy the whole piece anywhere like opgi or summin??

I see them on eBay all along.

You can still get the ported vacuum switch at your local parts house, they run about 8 bucks.

i kinda have the same problem my controls work except for when its on heater when its on heater it usually blows out of the defrost vents but everynow and again it will come out the vents and sometimes come out the vents when on defrost and some times the defrost wont work at all but only the heater am i in the same boat as everyone else do i just need a new switch? i took it apart and everything looked fine but i dunno maybe it has somethign to do with the doors not opening correctly some one help me out