VWVortex.com - How That Darned Vacuum Distributor Really Operates (a detailed analysis)

# Thread: How That Darned Vacuum Distributor Really Operates (a detailed analysis)

1. ALL OF THE DIAGRAMS IN THIS FIRST POST ARE NOT THE CORRECT WAY TO HOOK IT UP. THEY REPRESENT THE BENTLEY AND KAMMY "METHODS." See this post (within this thread) for the final proper hookup!
So... there seems to be much confusion and many people saying that Bentley is wrong in their diagram.
I'm going to prove, here and now, that they are not incorrect (I'm not saying they're correct either!) in their diagram, and hypothesize how this thing is really supposed to have you operate it.
I took apart my vacuum distributor to find out how it worked. It's rather simple really but requires a little bit of analysis to determine what it routes where and when.
Instead of taking pictures, in order to line things up I actually scanned the surfaces involved.
The bottom black part that the hoses connect to, without the white part on top:

Notice the little bity holes in the surface there. Those go to their closest hose connectors.
The top part, inside, rotated to represent the third (center-most) "Blue Spot" on the lever (remember you're looking at it from underneath here!)

Now the analysis. I mirrored the top part verticaly, aligned it to be on the same axis as the bottom, and rotated it to represent each of the positions on the lever. To see where the vacuum is going, I made little dots representative of where the holes on the bottom part are.
Yellow - Air recirculation; with vacuum, air is recirculated, no vacuum, no recirculation
Red - Center defrost/vent flap, with vacuum, air comes out center vents, without vacuum, air comes out defrost vents
Green - Bentley "vacuum boost" (I'll explain this later), Kammy hose from tank
Blue - Bentley hose from tank, Kammy footwell vent
Cyan - Bentley footwell vent, Kammy vacuum boost
I will reference some things here:
Bentley diagram -- diagram found on page 12-13 of the Bentley manual.
Kammy diagram -- http://dana.ucc.nau.edu/~kaw5/...m.jpg
The Manual -- the manual that comes with cabriolets from the dealer, essentially the "how it all should work"
In these images the arrows are reversed, since vacuum is the reverse of pressure, but I find it easier to think of in terms of the arrows pointing away from the source of vacuum.
Here we go.
Position 1, farthest left blue spot:

In this position it appears that it's set to do ... hmm... nothing. At all. vacuum is routed back through the center, meaning the vacuum escapes. If we were using Kammy's diagram instead, the vacuum would be closing the air recirculation flap to recirculate air, and opening the center vents. This actually fits the description of this position in the VW manual (the little silver one that comes with the car).
Kammy: 1
Bentley: 0
Position 2, middle blue spot:

In this position, again, we're doing nothing if we use Bentley's diagram. Air routed to center escapes.
In Kammy's diagram, the air is routed to a channel that escapes through the outside of the circle, which is confusing to me; I'm wondering if that outside area is meant to be vacuum tight, because most certainly it is not and would be very hard to make so. If it was vacuum tight, it would open the footwell vents.
Neither of these match the functions described in the manual -- since it says "air outlets" are the same as the first position which would have center vents open. This doesn't do that.
Kammy: 0
Bentley: -1
Position 3, last blue spot:

Using the bentley diagram this would have the center and air recirculation flaps operating. But that doesn't match the functions described in the manual either. To do that it would need to route it to the cyan outlet. Kammy's diagram would have it escaping once again going to the outer rim, and if vacuum tight, opening the footwell vents, which is half correct. If the vacuum booster works the way I think it does, it might then come back in through the port that the bentley connects the tank to and then also open the center vents. I still have to do some testing on the whole "vacuum booster" thing...
Kammy: 1
Bentley: -1.5
Position 4, first black spot:

According to bentley this would have air going to the outer rim and going to *both* of the ports of the footwell servo, one of which is supposed to be the vacuum booster return! Kammy's would have it doing the same thing just using different ports.
Kammy's would have it doing the same thing.
Kammy: 0
Bentley: -2.5
Position 5, middle black spot:

This is where bentley starts making a little sense. It routes the vacuum to the footwell vent servo and the air recirculation servo. The manual says fresh air is circulated, however. So this works only half way. If we use Kammy's diagram, we have escaping air (center vents opening if the outside rim holds vacuum)
Kammy: -1
Bentley: -2
Position 6, last black spot, defrost:

Another dead spot in the Bentley manual but this actually is how it's supposed to work. Kammy's is also dead (again, unless the outer rim is supposed to hold vacuum, in which case it would open the center vents and footwell vents, both wrong!)
Kammy: -2
Bentley: -1

Conclusion from this analysis? They're both totally wrong, according to The Manual. Bentley is just "Less wrong"
One thing that needs to be addressed is the green spot on this. According to bentley that's the "vacuum boost", where I assume vacuum from the footwell servo is fed back through to operate other things. The only problem is that if we use Bentley's diagram, that will escape right away unless the outer rim is vacuum tight which it is not.
I'm working on other arrangements that tries to make use of that vacuum boost, so stay tuned. We might be able to figure out the right arrangement knowing how the distributor distributes things.

Modified by Legoguy at 7:03 PM 10-18-2006
Updated with new images and corrections because apparently vaccum *is* supposed to be held throughout the outer rim (don't ask me how!)

Modified by Legoguy at 6:50 PM 10-20-2006

2. nice!
[IMG]http://*****************.com/smile/emthup.gif[/IMG] [IMG]http://*****************.com/smile/emthup.gif[/IMG]

3. I did something similar to this a fdw years ago. I put the lever in different positions and tested to see what I had on the various ports. The Bentley method worked closest to what I wanted it to do. And yes the outside ring shoud be vacuum tight and may have been when the car was new. Currently I can hear the air leak in the unit as it is. I'm thinking of shimming it to stop the loss.
FWIW I've pulled several of these out of junkyard cars and written down the "wiring/Plumbing" I found. I figure if the dash hasn't been tampered with the 'wiring" must be original. If so then VW uses the Bentley diagram! I've not bothered to mention it before since getting the mess to work at all is the real challenge.

4. So, if the outer ring should be vacuum tight, which I can't imagine how hard that would be for them to accomplish judging by the construction of the unit... I'll re-design the diagrams to show the flow better. I find it so hard to believe its vacuum tight because of the slot on the side of the white piece that metal piece goes into. The tab that fits into that slot isn't deep enough to make a seal when you put the two halves together!
Do you know if the places that are redirected to the center of the distributor are supposed to then kind of wrap behind and apply vacuum to the other ones that open to the outer rim?

Modified by Legoguy at 7:54 PM 10-18-2006

5. Updated images and descriptions to be a) more readable and b) reflect the assumption that it's supposed to hold vacuum in the outer area.

6. Nice analysis. [IMG]http://*****************.com/smile/emthup.gif[/IMG] I will concede that the footwell line may have been drawn to the wrong port, but until all of this is straigthened out, the diagram will remain unchanged. I'll take a look at ETKA tonight, because it too has a diagram that, IIRC, differs slightly from the Bentley diagram (not 100%, it's been a long while).
However...
 Quote, originally posted by Legoguy » This is where bentley starts making a little sense. It routes the vacuum to the footwell vent servo and the air recirculation servo. The manual says fresh air is recirculated, however. So this works only half way. If we use Kammy's diagram, we still have escaping air (center vents if the outside rim holds vacuum)

Key word there is "recirculated". It is not recirculated on that setting (it's not supposed to be anyway). The ONLY setting on which air is recirculated is position #1 (i.e., vacuum is applied to the servo in the rain tray which opens the flap -- closes off the square air hole -- allowing the cabin air to recirculate through the system, thereby cooling the interior much more quickly). In position #5, vacuum is applied to the footwell servo only; all other flaps remain closed (no air out of center vents, no air recirculated).
Question: What is the stock, original, from-the-factory settings for the vac lines? As I recall, I wrote down where all of the lines were before removing the distributor. When it came time to replace the lines, that is when I discovered that Bentley differed slightly (2 swapped lines).
Edit: Removed pic 'cuz my memory is shot to hell.

Modified by kamzcab86 at 12:35 AM 10-19-2006

7. When I said fresh air recirculated, I meant fresh air circulated, I thought I fixed that in one of my edits :/
I don't know the stock positions of the lines, for 2 reasons: I didn't mark them when I moved them myself, and even if I did, I wouldn't trust it because the P.O. appears to have been poking around in there. Because when I went to fix this whole thing, the hoses going from outside the interior to under the passenger side dash were flipped; ie, vacuum was being applied to the port of the distributor where the air recirculation flap should be and the air recirculation flap was hooked up to the port where vacuum tank should be.

Modified by Legoguy at 1:23 AM 10-19-2006

8. You did, but that was after I posted my reply.
I printed out the thread so I could look over the stuff while working tonight. The way I see it, there are actually only two positions that conceivably work with the vacuum supply being in the center, and one position that half works. The rest remain a mystery, make no sense (but there again, is there anything on a VW that DOES make any sense? ), on how they actually function, because to my eyes, vacuum is being cut off to servos that should be receiving it.
My engine is out of commission right now, so I can't crank the car on to do any re-testing (I do know that, except for the new center vent servo, everything worked just dandy before it was parked). I did get my MityVac out tonight and tested the two possible supply ports, but that proved to be pretty pointless other than discovering that the control mechanism isn't even attached to one of its brackets (plastic ) .
We need some kind person who still has the stock (untouched!) system to remove his/her radio and snap a pic.

Modified by kamzcab86 at 12:19 AM 10-19-2006

9. Word for word from *my* manual:
Upper lever positions
1 - Maximum cooling

Air conditioner is on. Cooled air is recirculated. No outside air enters the vehicle, thus keeping out dust, fumes, odors, etc.
Since no fresh outside air circulation takes place, we recommend to use this lever position primarily for fast cool-down, or for short and intermittent intervals only. Use the (logo for normal cooling) lever position for normal operation.
Air outlets
Cooled air is recirculated through dashboard vents 3 and 5 (previous page shows 3 = side vents, 5 = center vents). When lower lever is moved toward (heat), heated air is emitted from center dashboard vents 5, while cooled air flows from side dashboard vent 3. Only heated air temperature is adjustable (not sure if that's correct in practice).
2 - Normal cooling
Air conditioner is on. Fresh outside air is cooled and circulated.
Air outlets
Same as for lever position (Maximum cooling)
3 - Comfort setting
Air conditioner is on. Fresh outside air is cooled and circulated.
Air outlets
Cooled air is emitted from dashboard vents 3 and footwell outlets 4. When lower lever is moved toward (heat), heated air is emitted from center dashboard vents 5 and footwell outlets 4, while cooled air flows from side dashboard vents 3. Only heated air temperature is adjustable (again not sure if they're right)
the (comfort setting) position provides a pleasant sense of cool or warm comfort, since air is emitted simultaneously from upper and lower outlets.
4 - Ventilation
Air conditioner is off regardless of outside temperature.
Fresh outside air is circulated.
Air outlets
Fresh air is emitted from dashboard vents 3 and 5 (side and center). When moving lever toward (heat), heated air is emitted from center dashboard vents 5, while fresh outside air flows from side dashboard vents 3. The (ventilation) position provides a comfortable climate during moderate or cool seasons. With the air conditioner off, you also save fuel.
5 - Heating
Air conditioner is off regardless of outside temperature.
Fresh outside air is circulated.
Air outlets
Fresh air is emitted from windshield vents 1, side windows defroster/defogger nozzles 2, footwell outlets 4, and side dashboard vents 3 when opened. When moving lower lever toward (heat) heated air is emitted from footwell outlets 4. A portion of the heated air volume is also emitted from windshield vents 1 and side window nozzles 2. The (heating) position offers the most comfort during the winter months.
6 - Defrosting/defogging
Air conditioner is on. Fresh outside air is cooled and circulated.
Air outlets
Fresh air is emitted from windshield vents 1, side window nozzles 2, and open side dashboard vents 3. When lower lever is moved toward (heat), heated air is emitted from windshield 1 and side nozzles 2. Only heated air temperature is adjustable.
To achieve fast defrosting of windshield and side windows, move lower lever to extreme right and close side dashboard vents 3.

10. Note to self: never reply when in the middle of working. My manual says the exact same thing (actually, the supplement that came with my car is for the Scirocco -- I've since obtained the original '86 Cabriolet supplement --but it says the same thing); I merely broke it all down into more simplisitic wording for that ancient pic I had posted. Nevertheless, recirculated air occurs on position #1 only; that servo is activated when the lever is at position 1 and no others (the first illustration makes a tad bit of sense for this, but where is the vacuum supply coming from?). Illustrations 5 and 6 make perfect sense, if the center port is the vacuum supply. [IMG]http://*****************.com/smile/emthup.gif[/IMG]

11. I have Xander in my driveway at the moment for repairs. I'll check out the vacuum lines.
I too remember finding the vacuum lines (incoming) being reversed on my car compared to the Bentley if I recall correctly.
I decided to set mine up so the recirc flap was activated when in the heat mode so the warm air gets hotter. Made more sense to me since I needed heat and that's how I have it set up now.
I remember looking in my GTI manual and found a slightly diffferent "wiring" diagram than the Cabby Bentley. When I get home I'll post it.

12. By the way, in case I was unclear, the current images in the first post have a blue and a green vacuum path shown on them... green is Kammy's diagram, blue is Bentley's.
You know what? I'm starting to think that the reversed position, how I found it on my car, is actually *correct*! For two reasons: The hole in the plastic piece for that port is way bigger than the rest, and it's the only one that actually matches the description of (so far) the first two A/C positions. Still graphing the paths of it if that's how it's supposed to work.
 First 3 A/C positions are correct! Still testing...
 We have, now, the ACUTAL intended way this thing is supposed to work! I'm finishing the images and will get them up asap!
Modified by Legoguy at 2:55 PM 10-19-2006

Modified by Legoguy at 3:02 PM 10-19-2006

13. Alas, the goal of this thread complete! The correct "wiring" has been found!
I'm naming the "Legoguy diagram", after yours truly
Position 1:

Air recirculation check, center vents check!
Legoguy: 1
Position 2:

Center vents check!
Legoguy: 2
Position 3:

Footwell vents and center vents check!
Legoguy: 3
Position 4:

Center flap check!
Legoguy: 4
Position 5:

Full power to footwell vents check!
Legoguy: 5
Position 6:

Everything else vented, but the middle holds a vacuum, correct defrosting! Check!
Legoguy: 6

Notice that none of these positions require the outer rim to hold vacuum, which would be impossible as I've said because of the design of the distributor!
Now, go wire your system the right way [IMG]http://*****************.com/smile/emthup.gif[/IMG]
I'd like to thank Kammy for trying her best to get it right, but finding both hers and bentleys diagram wrong made me get it correct [IMG]http://*****************.com/smile/emthup.gif[/IMG]

14. Well, that would explain the <wooosh> I heard when applying vacuum to the thing last night. Now, it all makes sense; nice job, Andrew! [IMG]http://*****************.com/smile/emthup.gif[/IMG] I'll re-draw the diagram for CabbyInfo and give you the credit.

Just wait a moment..

I just updated that diagram to reflect changes I've made to which hoses go where on the footwell servo. The hose to the *top* is actually the servo, the hose to the *side* is the "vacuum booster" -- so I updated it to reflect that. I tested this in my car just now and I'm glad to report that it all works as it should! Wouldn't expect any different after proving it would by analyzing the distributor
I think the fact that both Bentley and Kammy's routed some vacuum to a position where it could all completely escape should have made them completely wrong in the first place. In the correct arrangement vacuum stays mostly in the system, and is only lost from the servos that are intentionally vented, and the response to the movement of the lever is almost instant.
Which is how it should be [IMG]http://*****************.com/smile/emthup.gif[/IMG]

Modified by Legoguy at 6:44 PM 10-19-2006

16.  Quote, originally posted by Legoguy » I think the fact that both Bentley and Kammy's routed some vacuum to a position where it could all completely escape should have made them completely wrong in the first place.

You would think that, but as I said, mine worked just dandy as it was.
While you were making ^that one, I re-did mine (been wanting to anyway).

17. Ok since we've reopened this can of worms I'll add a few. I've just checked my 83 GTI manual which has diagrams for the NA and German dashboards. So they show a photo of how the lines attach, a ink drawing of how they attach and another picture of how they attach in a pickup.
THEY'RE ALL FREAKING DIFFERENT! And if I remember correctly they don't match the Cabby Bentley (the lines are reversed if I recall)
The ink drawing exactly matches Lego's final version. The caption says ' Inset shows vacuum hose connections for 1981 and later German-Built models."
The diagram for the pickup is interesting since it shows a 5 position slider NOT a 6 like our cars. But the vacuum distributor looks the same.
So do we have differing wiring due to there being different v. distributors in different cars? Anyone wanna check out their EKTA part number for the pickup with AC vs. a Rabbit w/AC vs. a Cabby or Scirroco w/AC?

18. Oh and just for grins I'll mention that a similar system is in place in a Fox but it uses a pushbutton front panel that routes the vacuum. I almost put one in my cabby just to be different. It would easily replace the current slider panel.

19.  Quote, originally posted by Moljinar » THEY'RE ALL FREAKING DIFFERENT!

They're Volkswagens; of course they're all different!
I can check ETKA later tonight.

20. ETKA results: The Cabriolet vacuum pipe junction (aka distributor) is also used in the Scirocco ('82+) and Mk1 Jetta (replaces the original dropped part, however). The Germany-built Rabbit part is NLA, indicating that the part is/was not the same.
All other VWs from the era used a different type of vacuum routing system; however, the majority used the same vacuum servos.

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