AC/Heater Problems

Ok now that winter is starting to roll around I figure its time to fix the next thing in the list of probs this thing has. My AC sucks, but thats just because it needs recharged. My question is why do I only have extreme heat or Max AC...The dial on the dash that lets you select how hot or how cold (red to blue) does nothing. If I turn on the heat (on dash, floor any of the options) it blows nothing but heat no matter where the hot cold dial is. It would be nice to have a median temp. In the middle of winter we have to have the windows down and the heat on because it gets to hot with the windows up because I cant turn the heat down. How do I fix that? Also the part that I circled seems to have a vaccum that moves a plunger up and down and has to do with the heating. It leaks antifreeze and when the plunger is UP i have no heat and when its DOWN its all heat....is this the prob with the heating? Also the headlights are still not working.....New mulitifunction swith and headlight switch, and still nothing. I got a new connector because one of them that went into the back of the multifunction switch was melted. If this doesn't work I dont know what I'm going to do I'm about to lose my mind. HELP PLEASE
Ok it wont let me attatch a picture but anyway this thing is on the passener side towards the rear of the engine compartment. Its round about an inch around and 2 inches tall....it has a wire that connects to the top (The vaccum part?) and on the bottom is a metal piece that goes up and down. Email me if you want the pic [email protected] thanks