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    Thread: Center Vent / Vacuum Info

    1. Member kamzcab86's Avatar
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      07-17-2004 04:24 PM #1
      Rather than clogging up the other thread, I thought I'd start a new one regarding the center vent flap not working problem. (Of course, as I was in the middle of typing someone comes in who has to use my computer -- 2 hours later.... I find another computer to use and have to type from the beginning! )

      Anyway, I worked on the vent issue yesterday and discovered something in the process, so I'll get that out of the way first. The diagram in the Bentley for the vacuum lines attached to the vacuum distributor is slightly wrong. Bentley has the center line on side of the distributor going to the vacuum reservoir, when in fact the center line goes to the servo (I even reversed the lines to make sure):

      Second, all vacuum lines are good (in mine at least) -- no leaks.

      Okay, on to the problem. Running the A/C with the fan speed on 2 or 3 and dash-only selected, pushing the center vent flap in it stays open. Selecting dash-and-floor engages the servo (had my hand on it to make sure) and air comes out the floor vents and center vent (side vents in this whole story are irrelevant). Servo in question:

      After sliding the selector over to defrost, the center vent flap slammed shut immediately. Began the process again and then shut the car off. The center vent moves back and forth (distance of about 1/4") for about 10-15 seconds then appears to close. I say "appears" because it does drop but not all the way because 15 seconds later the flap slams all the way shut. According to Bentley, if the servo retracts before 1 minute has passed, one of four things is faulty: vacuum leak, faulty distributor and 2 other things I can't remember.

      So, unless Nrcabby can explain where that $5 vaccum part is on the heater core (couldn't find anything in ETKA), I shall be purchasing and installing a vacuum distributor to see if that solves the problem (the dealer was right afterall?! and was gonna charge me $250?!). If not, I'll just be propping the stupid flap open -- I mean really, why have a vacuum-operated flap when the vent has a built-in flap itself?!

      And for those wanting/needing to remove the center vent, here's a clear view of where the clip is:



      Modified by kamzcab86 at 10:57 AM 7-19-2004

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    2. Member Black_cabbie's Avatar
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      07-17-2004 04:42 PM #2
      First of all, do you have the egg carton thingy? Without it the center vent opens and closes anytime you hit the gas pedal. You need it to have constant pressure in the system.

      Now on to the center vents. There is a one way valve on the inlet manifold. If this valve goes bad the pressure is not held in the system so by the time you switch off the engine, the pressure is released back to the inlet manifold and the vents close.

      I might have a photo somewhere......

      Btw, the last photo of you under the dashboard is the correct position to work on the fusebox and any electrics on the car.

      Chip Tuning for a living @ www.microchips-tuning.com

    3. Member kamzcab86's Avatar
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      07-17-2004 05:45 PM #3
      Yes, she's had her eggs since she was new and hasn't dropped any in 18 years .

      As for the one-way valve, I'll check that out, but when it was in the shop I believe it was looked at and found to be okay. What's the best way to check to see if it's functioning correctly?

      What's throwing my suspicion toward the vac distributor is that while the car and A/C were running, I switched it over to defrost which immediately slammed shut the center vent (if I remember from a few years ago when it worked, it eased shut) and air flowed from the defrost vents. Would this be an indication that the valve has gone bad? I can understand the shutting-the-engine-off part leading to the valve though. Plus, the vac dist. sounds crappy when the lever is moved.

      I'll rule out anything and everything before replacing the vac dist. or so help me any of those friggin' servos! (which appear to be functioning just dandy thankfully ).

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    4. 07-18-2004 05:04 PM #4
      the difference before and after (a few years of difference) is that at the begining the flaps have anice foam cushion so the flaps don't make noise, after a while the foam just crumbles and get's blown evrywhere little by little

      the non-return check valve in the engine compartment can be checked by removing it and blowing and sucking on one end, it should allow flow going in one direction but no in the opposite direction, I removed the eggcrate thing on almost all my cars and just installad a second check valve in line to keep vacuum in the system


    5. 07-18-2004 09:09 PM #5
      Quote, originally posted by kamzcab86 »

      So, unless Nrcabby can explain where that $5 vaccum part is on the heater core (couldn't find anything in ETKA)

      When I fixed mine I had to replace the check valve that steve was talking about. I forget where I got it but I paid less then 10 bucks for it and it fixed my vent problems.

      Quote, originally posted by stevelangford »

      the non-return check valve in the engine compartment can be checked by removing it and blowing and sucking on one end, it should allow flow going in one direction but no in the opposite direction


    6. Member Moljinar's Avatar
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      07-19-2004 11:55 AM #6
      BTW I found an excellent vacuum diagram in my GTI manual!! Much better diagram than the one in my Cabby manual.

    7. 07-19-2004 12:32 PM #7
      Ok, this is starting to sound too familiar......

      I've got the following issue:

      Turn on the AC, and I get cold air out my side vents, but hot air out my center vent. Could I be a victim to this vacuum issue as well...

      I havent even started thinking about tracking it, down and have just been going top down all the time when its hot.


    8. Member kamzcab86's Avatar
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      07-19-2004 01:59 PM #8
      Quote, originally posted by Nrcabby »
      When I fixed mine I had to replace the check valve that steve was talking about. I forget where I got it but I paid less then 10 bucks for it and it fixed my vent problems.

      Okay, will remove the valve later in the week, double-check that's it working or not and go from there... thanks guys!

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    9. Member Moljinar's Avatar
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      07-19-2004 03:33 PM #9
      Quote, originally posted by 90RedCabrio »
      Ok, this is starting to sound too familiar......

      I've got the following issue:

      Turn on the AC, and I get cold air out my side vents, but hot air out my center vent. Could I be a victim to this vacuum issue as well...

      Yup that's it. You NEVER get cold air from the center vent. Not made to do that. Hot air will come out of it if the vent flap is open. It's normally closed by springaction and opened by a vacuum solenoid.


    10. Member kamzcab86's Avatar
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      07-19-2004 04:11 PM #10
      Quote, originally posted by Moljinar »

      Yup that's it. You NEVER get cold air from the center vent. Not made to do that. Hot air will come out of it if the vent flap is open. It's normally closed by springaction and opened by a vacuum solenoid.

      All vents, except the side vents, provide cooled, heated or fresh air; the side vents provide only cooled and fresh air, they do not provide heated air (according to the '86 manual). My Cab and Mom's '84 Rabbit 'vert operate this way, (which is why it's so annoying that the center flap on mine doesn't open on its own any more). If only heat is coming out the center vent when the A/C is on, something is wrong in the system.

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    11. Member Moljinar's Avatar
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      07-19-2004 05:13 PM #11
      Hmmm, not to disagree but my dissection of a heater box showed no way for cold AC air to go anywhere except to the side vents. I'll double check when I get home tonite.

    12. Member kamzcab86's Avatar
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      07-19-2004 06:12 PM #12
      That is sooo wierd! Cold air has always come out my center vents (along with heat or fresh air when those were selected) and my owner's manual shows that. Hmmmm....
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    13. Member atomicalex's Avatar
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      07-20-2004 10:33 AM #13
      kaz, my 82 is that way - the center blows fresh or hot depending on what is selected. I have no A/C anymore, so I never get cool air unless it is cold out.
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    14. Member Moljinar's Avatar
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      07-20-2004 10:47 AM #14
      Quote, originally posted by kamzcab86 »
      That is sooo wierd! Cold air has always come out my center vents (along with heat or fresh air when those were selected) and my owner's manual shows that. Hmmmm....

      I double checked my heater box and there is a wall between theAC side and the center vent. AC can ONLY go to the side vents and no hot can get to the side vents.

      There is a thread in the A1 forum on how to modify your heater box to make it do both (basically cut out the wall)


    15. Member kamzcab86's Avatar
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      07-20-2004 04:59 PM #15
      More info on the heat-only-out-center-vent problem (may look familiar to those who are in the Yahoo group; compiled and cleaned up the spelling/grammar a bit):

      Quote, originally posted by Yahoo Cabriolet Group »
      Hey, I got a 89 cabby and when I use any air settings including A/C the front defroster blows out hot air, the defroster turns on at the same time and runs at the same air settings. The switch is fine being that I can put the a/c at 1,2,3, or 4 an cold air comes out of the vents, but the defroster seems to like those settings also because it spits out hot air on the same air speed settings. It’s unbearable to drive even with the top down; it heats up so much the dash gets to be so hot u can’t touch it. I also had took out my cd player cause it started to heat that up so bad I could smell burning. I don’t know what the deal is with it. Someone said the wires from the a/c and heater could be crossed when they get to the blower but I’m not sure.. HELP PLEASE!! Being like this in the summer SUCKS!

      If your defroster is continuously spitting out hot, then I would suspect that the cable that controls the heater valve on the firewall is broken, or severely maladjusted. You can check this by moving the selector to full hot, then go out under the hood and look for the two heater hoses that are in the middle of the firewall. On one of them usually closest to you there is a plastic valve. Look to see if it is against the stop. Now move the slide selector all the way cold it should move the valve against the other stop, if it isn't then the cable is broke. It really isn't a cable but a steel wire inside of a shield. To turn the valve off, just move it to the stop.

      You didn't say if your defroster is on all the time or is the only thing that is working. Ie: can’t go from defrost to front vents.

      It does continuously spit out hot air, even if the speed selector that controls the air on all settings is off. No air comes out of the defroster but in about 10 min. the whole dash is hot, so something’s heating up back there... the a/c is fine though; cold air comes out of the vents -- except the center 2 vents (the valve in the back of the center vents is stuck shut).

      I know that the valve back their diverts cold air from the defroster to the center vents; mine is stuck shut so that explains why air is coming out of the defroster ports all the time but it doesn’t explain why its hot air all the time even if the a/c's on. Any ideas on how to fix that valve in the back would be helpful 2.

      Better advice than I could have come up with - find one and compare it to yours...

      If one vent (defroster) is open, the other (center cold air) is usually closed, just like you describe. The "default," I believe, is the defroster setting. Some people have just disconnected their levers and closed off one or the other manually according to season.

      It does also sound like the heater valve is stuck open. It is accessible in the engine bay. Check the cable before you try to replace it - it may be stuck on something.

      Sounds like you have two problems, one is the vacuum servo is stuck that puts the heater air in the heater box. The second thing is that the heater control valve is always on. I suspect that the cable may be off the arm on the valve, and your valve is in the on position.

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