1986 Sedan. Just got home from a 5x hour ride. Raining all thru ride. Windshield was fogged thruout ride. Reason : Switches/button you push to choose defroster, feet, etc. is not working. Air just blows straight out. System that lets you choose blower direction is not electrical but rather it appears to be vacuum operated. So questions are : Where should I start looking for source of problem ? How should I test ? I'm thinking the 3 button switch might need replacing. If not that then a vaccum hose might be bad ? Or a hose connector ? Any help and info on resolving this problem would be most greatly appreciated.

Just finished fixing this problem. Turned out problem was under hood : vacuum hose/line coming from intake manifold valve was broken at bend where it goes thru firewall into inside of car. I got a connector(by the way 7/64" connectors are not too easy to find . I ended up having to try 3x different parts places)and connected a foot or so of new hose/line from where it broke to intake manifold valve. It works 100% fine now. Thanks so very much to those who replyed to me. Once again i must say what a wonderful resource and community of like minded and very helpful folks brickboard is.

First valve to check is the check valve. It is that white and black plastic valve at the top of the manifold under the hood - held in place by a short section of 3/8" hose. The thin line coming from it goes through the firewall to a vacuum storage bottle that looks like three tennis balls behind the center console.
--
Art Benstein near Baltimore

The vents through which air is blown from the dash, into the footwells, and up to the windshield are each controlled by small vacuum-powered actuators. Engine vacuum is obtained from the intake manifold, and routed through through the firewall to the three-button panel, which, in turn, routes the vacuum to the actuators. Everything is connected by small rubber tubing.

Usually what happens is that the tubing gets old, splits, and leaks vacuum. If you have no control over air direction at all, that suggests that the fault (i.e., the leak) is somethwere between the intake manifold and the three-button panel. You'll have to locate and carefully examine the rubber hoses, find the leak, and replace the defective hose(s). Pay particular attention to the ends, which fail first. If the hoses are long enough, you might consider snipping off the end 1/2" of each end of each hose.
--
David Brick, Santa Cruz CA, 1988 245

"If not that then a vaccum hose might be bad ? Or a hose connector ?'
Good place to start. If lucky, the source hose (thats what I call the hose that goes to the three buttons), may have come loose. Requires your crawling around under your dash, and following the vac hoses. Doubt that it would be the push buttons....but check their hoses, and connectors.

Enjoy .
--
84, 242GLTi, 167K, 4+OD, in rehab; 89, 245 DL, 308K, M 47, daily driver; 93, 245, auto, 167K ; and other toys.

Any idea how frequently the buttons themselves do fail?

I'm fairly confident that I've had one (the recirc button) go bad, as it would constantly hiss indicating a vacuum leak, regardless of whether in or out. (for a while, I could wedge the button to the side with a piece of paper folded up, and that halted the noise for quite a few months.) I don't believe it's the vacuum line from the button to the servo, as if I clamp that line a couple of inches behind the console, the hissing remains, and of course, if I clamp the vacuum source line, the hissing goes away.

There remains the possibility that the line to the servo is cracked right at the junction to the switch, however, I've looked at the line, and it seems ok. For now, I've simply blocked the vacuum line in front of the firewall. better than the incessant hisssss.

I've tried once to get the 3 button console unit out from the dash, however, my progress was stymied, I think by the metal bars to the side. I'll have to give it another whack, if I can find the unit somewheres.

just curious if anyone else has had the switch fail.
thanks,
link