Yeah that was the simple "wife-friendly" version. Getting into the details things are a bit more complicated
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AC/Heater system-
I haven't gotten to prying the knobs off the control yet but did take some time tonight to figure out how it all works. Good thing I did because at least a pair of the vacuum hoses were hooked up backward, which explains why my bi-level never worked right. For those that are interested here is what I learned:
There are four vacuum cans that operate dampers in the vent system. All of these are controlled by the upper slider through a multi-position vacuum switch. The vacuum can in the passenger's side kick panel controls whether air is recirculated or whether fresh air is drawn in from the cowl. It has two vacuum hoses connected to it (more about this in a bit). The vacuum can at the left end of the heater box controls whether air is directed to the lower heat vent or the defrost duct. There are also two vacuum cans behind the heater box. When the lower one opens its damper it directs air to the dash (A/C) ducts. When the upper one opens its damper, it too directs air to the dash ducts, but the upper damper also blocks air from going to the heater/defrost when in the open position. In the closed position air is free to travel through the system to the heater/defrost damper.
The bottom slider actuates the main damper and the vacuum switch for the water cutoff. In the hot position all of the air is directed through the heater core. In the cold position all of the forced air is directed around the heater core. But even in the cold position the heater core is not isolated- there is still an open path from the core to the heater outlet. So the system relies on the water cutoff to completely shut off the heat.
Back to the top slider.
In off position vacuum is cut off from all of the vacuum cans. This leaves the fresh air damper in the recirculate position (no fresh air). The heat/defrost damper is in the heat position and both of the dampers behind the box are closed, sealing off the A/C ducts but keeping the path to the heat/defrost damper open.
In the A/C position vacuum is directed to all the cans. That means 100% fresh air is drawn in, and both the upper and lower dampers direct air into the A/C ducts.
In heat position vacuum is directed just to the two hose connections on the fresh air can in the kick panel so that 100% fresh air enters the system. Remember the path to the floor heat vent is wide open as the default, even with the system off.
defrost position is the same as heat except vacuum is also applied to the heater/defrost damper which directs the air into the defroster vent.
In bi-level position vacuum is directed to the lower damper which allows air into the A/C vent system. The upper damper stays closed so air can also pass through to the floor vent. (I found my hoses for the upper/lower cans were reversed, so that bi-level only allowed air to the A/C vents through the upper damper.)
The kick panel vent is fully open so that 100% fresh air enters in all of the above operating positions. In inside position however vacuum is only directed to one of the connections on the can (remember there are two hose connections) which partially opens the damper. So there is actually a blend of inside and outside air, and otherwise everything is the same as AC mode. I was surprised to discover this- and it leads to a question. As my system was hooked up vacuum was applied to the middle hose connection on the can, which opens the damper about 80% (meaning 80% of the air would still be fresh.) By swapping the hoses so that the vacuum is applied only to the secondary connection on the can the damper will only open about 20%, which means 80% of the air would come from inside the car. To me this makes more sense for inside position on the control.
I haven't traced out all the electricals but that looks pretty straightforward. There is a master switch that engages power to the system in all positions but off. The fan switch directs power to the master relay and selects the appropriate resistors in the engine bay. And it looks like the norm/vent switch is just a cutoff for the compressor- there are no electrical connections to any of the dampers so it can't affect airflow.
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And a link to the thread that I ran when I was going through all this:
http://forums.maxperformanceinc.com/...=638353&page=2
From what you describe your cutoff valve may be frozen. Easy to check if it's working- with the system in cool position the heater hoses at the valve should not be hot since the valve should prevent water from flowing through them. Then if you push the lower slider to the right the valve should open and the hoses should quickly get very hot.
Also if you are getting a lot of air with the fan off, then maybe the fresh air damper in the kick panel is not closing. Easy to check that too. Just pull the passenger kick panel and watch what it does in the various selector positions. It should be fully closed with the system off.