So bear with me as I tend to be long winded and I know there's a few posts of this already. I'm in the process of reinstalling my dash with some new pieces here and there. One of them is a brand new ac/heater control selector. I decided, before I get too far to temporarily plug this in (thought this was my problem) and start the car to see what happens.

Basically, the problem is much like the other posts. I have air coming out of vents, defroster and sometimes heater (lower) vents. No matter where I put the selector the air fails to come out at the right spot, and as of now it doesn't appear to be moving at all. After the new control unit didn't work I decided to check my vacuum lines. The small black one that comes out of the firewall looked kinda iffy where it was connected, so I put it right on a vacuum port on my Mighty Demon carb (this carb connection I use normally with the lights and air control line coming out of the firewall) so I it should be enough vacuum to make things work, especially with only the one line being connected now. Start the car up and nothing happens, same thing blowing out wherever but the right places.

I went as far as hooking up my might vac and trying to pull a vacuum on that black line to see if the zone diaphragm rod moved and it did not. Next I pulled the firewall bushing out and I can see the three lines connected on the backside. Visually, from what I can tell, the lines look good on the inside of the car and none of them are brittle. I see a couple Ts in there too that look good (took off glove box) yet vacuum doesn't seem to exist or do anything. I also pulled the black line from the engine compartment out then reinstalled into the firewall bushing but nothing seems to change. I might add that when I had the dash out I had removed the piece of duct work that has the zone controller on it and when I sucked on the line it operated easily and held, so no leaks there. No leaks at the passenger side vent diaphragm either. Any thoughts?

 

no pics on my end

 

I have posted several questions myself. I just ordered all new parts to rebuild the A/C control. Maybe you can help me with a similar question. How many vacume lines come out of the defroster Diaphragm? Mine has 2, but the assembly manual only shows one. No matter how hard I try, I cannot get any of my diaphragms to move. The vacume from the main source line does not appear strong enough to counter the heavy spring loads holding the vents close -- HELP!!!

 

Pics don't work for me. Do you have the assembly instruction manual (AIM)? While it isn't a How-To, the AIM has the best diagnostic diagrams for the proper routing and correct color coding of the various vacuum lines for the AC/defrost system. Easy to test with a My-T-Vac.

 

Hrm, no idea why the pics aren't working now, they were here when I made the thread. I suppose the links could have changed, I'll check them later.

TyCor, my vette has only 1 vacuum line going to the defroster diaphragm. When I had all my stuff out I could suck on mine and it would easily move the spring. All my lines look like they're in good shape but I must have a leak somewhere.

Easy Mike, no assembly manual and I tried mighty vac on the main vacuum source and nothing seems to happen. I guess I need to dig in further. I didn't really want to take the dash off again.