# MK I ventilation control problem



## daegal (Nov 27, 2009)

Hi All, first post to the forum here.
I've owned a Mk I in some form or other since my purchase of a new '83 GTI. Currently I have an '89 Cabriolet (best one I've owned) that's in great shape. Over the years I've done everthing on these cars from swapping motors to complete rebuilds but I've come across a problem that's got me stumped and hoping 'yall might be able to help. It seems there's a problem with the ventilation controls not being able to change direction, i.e., heat, defrost, etc. I know it's contolled by vacuum and I replaced the dash controls (what a P.I.A.) but that didn't help. I'm figuring it must be one of the vacuum servos or a check valve somewhere as I can hear a wheezing sound when I let off the throttle. So I'd like to know if anyone's had a similar problem and what the fix might be before I go tearing the dash apart to find it. Thanks in advance for your help!


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## where_2 (Jul 21, 2003)

*Re: MK I ventilation control problem (daegal)*

In my last Mk1, ('80 Scirocco_S), I had an issue with the controls which you've already dealt with. There are certainly opportunities to leak vacuum at each of the actuators, and you should be able to test each of them separately with a hand-held vacuum pump that has a dial gauge on it. The dash control has certain positions where it intentionally allows the vacuum to escape to open certain actuators, but all those actuators that attach to the back of the control unit should be closed ended systems that can hold a vacuum when you draw one using the hand-held pump. 
However, it sounds as if you may have a leak elsewhere. I would begin by checking in the engine bay where the hard plastic lines are subject to additional heat (in comparison to the passenger compartment). I would also check the vacuum reservoir (it looks like an egg-crate). Sometimes the reservoir was mounted behind the plastic fender liners, in your '83 it probably hung from the under side of the hood. If you look around the engine bay, you'll probably see a tell-tale plastic vacuum line heading into some hidden area, and that's where I'd look for the reservoir. 
Another thing to check is that the vacuum check valve is functioning. Somewhere between the intake manifold and the vacuum reservoir there will be a one-way check valve that should keep the vacuum in the reservoir for atleast a minute after the engine shuts down. This same principle is what allows you to still keep control of the air ducting when you're running full throttle. At full throttle, you're developing no significant vacuum and it would be quite annoying if your air ducts went nuts every time you accelerated. If the check valve is shot, this is one of the more common symptoms.


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## daegal (Nov 27, 2009)

*Re: MK I ventilation control problem (where_2)*

Great, thanks! I'll check it out


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