I have been trying diligently to fix my AC/Heat system. After reading many many posts I began to realize that something was wrong with the vacuum system in it. I started under the dash traceing the vacuum lines and I found that there was a major crack where the vacuum line goes in to the magnetic switches. This allowed the water ****, the outsite air and the mode door vacuum switches to function.

I am left with one minor issue with it. When I go from AC towards defrost everything moves and doors open and close just fine. But when I do the opposite going from Defrost Hot to AC cold the mode door will not drop down to close the heating unit and redirect the air back out the front. If I shut the car off then turn back on again the door is then in the AC position.

Of course I can live with this but it sure would be nice if the AC/Heat system was working perfectly.

Doesn't one or both of the magnetic switches also release to atmosphere so that the vacuum can let go? When you turn the key off, you're de-energizing the switch. Find out why that switch still has power when you're telling it to let go.

Yea, I figured it was something like that. I do not know where to look so I guess unless someone knows, I will just live with it.

I don't know if your '76 is configured like my '78, but it's not necessary (in my year) for the magnet valve to work. In fact of my two magnet valves, the only one that works is the one that actuates the high idle for the AC.

A problem that I did have on my '78 was a gummed up and leaky mode selector vacuum switch. That might be your problem. For more info, see a thread I started here:

http://www.classiczcars.com/forums/showthread.php?35521-Refurbishing-the-HVAC-vacuum-selector-valve-in-a-1978-280Z-useful-info&highlight=