I vacuum tested all of my actuators and they all work fine and the vacuum holds and there are no leaks. I have vacuum from the black hose and seems to be constant. I have a reading of about -18 -20 in. per the gauge I'm using.

I replaced the switch and still no defrost or vents. The lever doesn't seem to do anything. I've tried 2 switches with the same results. What are the chances of buying a bad switch from a dealer? Any ideas of what else my problem could be??  

You say you changed the switch?  There is a vacuum selector which changes the output of the vacuum and directs it to the selected actuator.  It should be beside the electrical switch on the heater control. My 84 has a round disc about the size of a quarter made of orange silicone rubber.  It had a small tear in it.  Crazy glue and some silicone lube fixed the problem.

James  

I had posted a similar problem (I think) now that I remember the vacuum issues under the dash, but I posted it in the technical pages under 1978 Hot Interior...

-- a snip here --

Can anyone help?
My cabin is always extremely hot!!! It can be hot or cold outside, but it feels like 100 inside. The temp sliding bar works, and I can hear a thump when it seems to close the fresh air door. The fan works, but doesn't seem to go on super-high, nor does the air seem to kick in. All the fuses in the block look good. The vents at the top center and sides don't seem to blow, yet hot air streams out by my legs.