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Retrofitting non-A/C ventilation ducts

As the final step in the removal of the air conditioning system from my 77 911 that I started nearly 20 years ago, I finally started work on replacing the ventilation ducts with the proper non-A/C setup. Why? Because in 1977 when Porsche added a center dash vent and changed over to using in-dash vents rather than an under-dash system for A/C output, the dash vents were dedicated to only air conditioned ventilation. So when the A/C is removed, these dash vents are no longer functional for any air flow.

From looking at PET, it appears that the basic A/C duct system for 77 was used from 75-77, and changed slightly in 78 for the SC's. I believe the same limitations apply for early SC's as far as where the A/C air is directed. However the diagrams show that changes were made in 82 which may have added some flexibility in this area - it's hard to tell. SC owner please chime in if you know.

Regardless, the non-A/C system appears to be the same from 77-83, so the following conversion should apply.

Note that I conveniently have the gas tank out of my car as part of a much larger suspension rebuild project I started last winter that has grown into many tangential projects (see Time to replace 30 year old suspension - little help please?). This makes the task a lot easier as I can simply sit in my trunk area and do the work .

I am approaching this project in three phases:
  1. Research the two systems to find out differences and the parts needed (done)
  2. Disassemble the current system, install the parts I have already acquired and make a list of the parts I need to finish the project (in progress)
  3. Order the remaining pieces and finish installation. (next step)


This first picture shows the ventilation duct system from a 77 911 with A/C. I have annotated the diagram to show where the Hot (red), A/C (blue) and Fresh (green) air flow. From this diagram, it's easy to see why the center and side dash vents can only deliver A/C air.




This next picture shows the ventilation system from a 77-83 911 without A/C. Again, I annotated the Hot and Fresh air flows. Note that only fresh air can be delivered to the center vent, but the side vents can be used for fresh and/or hot air as set via the ventilation controls (good for defrosting side windows). Also note that since the center vent taps its flow from the right side fresh air source, the passenger (for LHD) will not get as much fresh air to the defroster or footwell (I guess this makes sense). I believe this is reversed for RHD.




Based on these two pictures, the parts needed to retrofit the non-A/C system into a A/C car are shown in red in the third picture below. Two additional clamps #23 will be needed as well. Note that you won't need to acquire the duct going to the center vent (part #22) as this is the same as part #3 in the first picture and can be re-used (473.261.233.A).



The part numbers and our current host's prices are:

Part #20: 911.571.039.00 "distribution piece" $27
Part #21: 911.571.239.00 "air hose" $2.50

So far, so good on the cost of this project (if these are still available). Now, here's the problem. As you can see in the picture, the control boxes (#18, which direct the fresh/hot air up/down) are different for the A/C Vs. non-A/C cars. The non-A/C control boxes have an extra little duct coming off the top cap which forks off some of the airflow to the side dash vents. Actually, all that is different between the two control boxes is this plastic cap on top. But, unfortunately, you can't buy just the cap, you have to buy the whole control box. Of course these original ones are NLA and have been superseded to the SC part. And to top things off, they are expensive if you want to buy them new (~$300R & $450L). The best thing is to try to find a used set from a non-A/C 74-83 911. I'm not sure how may SC's were imported without A/C so your search may be narrowed to 74-77. If you're lucky (as I was), you might be able to find someone willing to sell you just the L&R caps and not the whole control boxes. The non-A/C caps look like this:



the A/C counterpart looks like this:



If I was unable to locate a non-A/C cap, the other option was to fasten a piece of tubing to my existing cap (that's what it appears the factory did anyway). My concern was that in addition, the non-A/C caps have a baffle in them just aft of the small duct. My assumption is that the baffle is there to help divert some of the airflow to the small duct (I doubt it would get much otherwise). Here's a picture of what the baffle looks like:



If I modified my A/C caps to be like non-A/C caps, I would have to add this baffle as well. But, when I pulled the cap off the car today, I was surprised to see that they left the baffle in there, even without the small duct. This seems strange as would certainly impede airflow to the windshield defrosters. Anyone know why this is there? The good news is that there would be less work to do if one wanted to convert an A/C cap to a non-A/C cap. Here's the obligatory picture (sorry about the quality on this one):




I'll stop here for tonight. I'm heading out to the garage to work on the disassembly a little more and take some pictures. I'll post a follow-up of my progress tomorrow.

Frank
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Old 01-05-2008, 08:23 PM
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For what it's worth, here's a picture of a ROW '77 911 without A/C.

JR


Old 01-09-2008, 03:12 AM
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Javadog,

Thanks so much - that picture is extremely helpful, especially since mine is a 77 as well.

But, the plot thickens - I did not realize that the splitter duct coming off the right fan housing has control lever linkage attached to it (red circle)! At first I couldn't see why that would be necessary, but then I started thinking about it and it makes sense. When the fresh air is closed off (top left lever to left) and the heat exchanger valves are open, if this path to the center vent was not closed off as well, then some of the hot air from the right control box would find its way to the center dash vent. As if this system wasn't convoluted enough . I sure hope that little piece of linkage comes with the splitter duct because I don't see it on the parts diagram. If you have any closer pictures of this linkage that would be very helpful. Hmmm, after looking at that picture again and thinking some more, its function may be more than that based on something I read in the owner's manual on the center vent. I'll post a follow-up once I learn more.

One question - the cover plate shown in the yellow circle, is that something you fabricated? It seems the OEM plate there was some type of pressed fiber which is NLA. I saw your post on the recent thread about this formed cardboard cover plate



Frank
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Old 01-09-2008, 08:45 PM
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I think someone started making those plates again. http://www.appbiz.com/ Maybe these guys as a custom job. Try a search to be sure.
Old 01-09-2008, 08:50 PM
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formed cardboard cover plate

N/M

That is a reproduction of the old cardboard one, but at least it's available.
Old 01-09-2008, 08:54 PM
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Frank,

Yes, I have a closer photo of the linkage, which is reproduced below. Also, take a look at the detail shots of the housing. There is a bend in one of the rods that won't be obvious from the first picture.

As for the cover, there was not one there so I made one from sheet metal and a cork gasket. Ironically, the pressed cardboard cover mentioned in the other thread was what the factory used to plug the hole in the right inner fender adjacent to the hood shock. A similar hole exists in the left inner fender for the duel filler pipe to pass through. This particular car was delivered to a customer in Germany and never had an A/C system, nor the cover over that hole behind the smugglers box. I just wanted to plug the hole. There are a couple of part numbers for things that might be the correct cover; I just never bothered to order any of them.

There are a couple of other points I might make. The center vents on these cars had dampers built in that allowed the flow of air through them to be cut off completely. On some cars, the fresh air blower housings had only one butterfly valve to shut off air flow to the distribution boxes, even though the linkage is there for both of them. You can add a second valve if you like, as the dampers in the vents don't always stop 100% of the airflow. You'll want to replace all of the foam seals at the valves, as by now they are probably all crumbling. You can't buy them, so they have to be made from thin foam sheets. I usually use material designed for damping sheet metal in stereo installations.

The last photo is of a system in a 1980 ROW 930 that at one point had A/C. It has been removed and a second butterfly valve added to the fresh air blower housing.

Hope this helps,
JR





Old 01-10-2008, 04:24 AM
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JR,

Thanks again for these great pictures, they sure help clear up some things. But I'm still at a loss regarding one aspect of the fresh air flow. In your post you mention:

Quote:
Originally Posted by javadog View Post
On some cars, the fresh air blower housings had only one butterfly valve to shut off air flow to the distribution boxes, even though the linkage is there for both of them.
This comment really piques my interest. So, referring to the photo below, are you saying that there is no valve in position #2 on your car (there is on mine)? If that's the case, then I would expect there to be two different part #s for the blowers (A/C & non-A/C), but they are the same (911.571.018.00) - even for RoW.




However, not having valve #2 would make perfect sense for the following from the 77 owner's manual:



Note the ventilation controls in the red box. The description below that figure states "For maximum ventilation of car interior, open center outlets." Now, if the top left lever is all the way to the left as shown in the figure, then according to the text in the yellow box "fresh air ducts closed. No fresh air supply from the outside" does not compute.

If there were valves at positions 1 & 2, then a) why would one close them to get "maximum ventilation", and b) why in the world would one turn on the fresh air fan (top right lever to the right) if both the valves out of the box were closed? This picture only makes sense if there is no valve #2. Could you possible verify this? The owners manual mentions several times to "close center outlets" when the top left lever is to the left, so I am assuming that the center vent always gets fresh air when in this position, and the driver uses the valve at the vent itself to turn the flow on/off, rather than the controls. This also would explain why there are two separate top levers for the non-AC cars, rather than a single lever. So, strictly speaking, the description in the yellow box is not accurate, if my assumptions are correct. The top left lever really controls whether fresh air goes to the center vent or the L/R control boxes. This is starting to make sense - again, only if there is no valve #2.

Boy, of all the sub-projects this suspension rebuild has put me on, I figured this had to be the easiest - I should have known.

btw, the part in the yellow circle I believe (hope) is part #20 in the part diagrams at the start of the thread, and not part of the fan housing.

Frank
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Old 01-11-2008, 08:50 PM
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Frank,

There are a couple of ways to arrange this. If you look at the pictures of the white car and the brown car, you'll see both of them. On the white car, with part number 20 (which is a seperate part from the housing; it's held on with two cheese head screws, one of which is visible in the photos) you don't need the second butterfly valve at position 2 in your photo. With the arrangement on the brown car, which lacks that extra valve, you do need both butterflies. On the blower housings that have only one butterfly, the linkage and the shaft for it are there so all you have to do is steal the plate from another housing and install it.

For what it's worth, the systems with the single upper lever and the two upper levers work about the same in practice. With the single lever, the fan doesn't start until the lever is halfway to the right, at which point the valves are half open. On the double lever systems, by the time you open the valves halfway, you are forced to start the fan, as the two levers hit and you can't open the valves any further unless you run the fan.

Take a look at what you currently have on your car. Then decide whether you want to get the extra distribution piece (number 20, Pelican shows in it their catalog for $27, I'd assume the rod would be a few bucks more) or go with the arrangement on the brown car, shown earlier. Either way works.

JR
Old 01-12-2008, 03:32 AM
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JR,

Of the two ways of doing this that you show, I like the OEM way better. It seems the configuration in the brown car would not yield much air flow to the center vent with the duct coming off at a right angle like that.

I already ordered part #20 about a week ago, but it has to come from Germany and will take 2-3 weeks to get here. Your comment about moving the butterfly valve from #2 on the picture to #3 makes a lot of sense. I won't know if the part will come with a butterfly pre-installed or not until it arrives. I'll go out and take a look at my system today to see if the butterfly can be removed. And as I said earlier, I hope it has the little linkage piece attached because I don't see that on PET.

Regarding the 1 vs 2 top lever vent controls, I originally shared your opinion that it really didn't make much difference, since as you state, in order to get the fresh air valve all the way open, you have to move the fan lever to the right anyway, so why not just have one lever. But from what I can tell, there does seem to be an advantage to the two lever system, which only makes sense in cars with no A/C and with a center dash vent (and no valve #2). From the PET, it looks like Porsche introduced the two lever design at the same time as the center dash vent (new part # 911.613.111.08 (vs. .03 for single lever)). And the reason for this is to be able to set levers as in the red box from the owners manual picture above. With a single lever, if you want forced (i.e. fan) air out of the center vent, you would have to move the lever over at least half way to even begin to engage the fan. However, doing so begins to cut off the air flow to the center vent as it moves the new butterfly valve #3 in the splitter box. And the further the top lever is moved to the right to increase the fan speed, the more valve #3 redirects the air to the right control box (feet or windshield) and away from the center vent. If this is correct, then I will do the job right and replace the ventilation control lever assembly as well. It's hard to tell, but from the picture it appears that valve #3, even when fully up, does not completely close off the flow to the center vent in order to allow some air to bypass it in this position, which would make sense. Again, I'll know more once the part arrives.

I actually have a new 2 lever vent control system I picked up at a Stoddard swap meet many years ago for this project. However I did notice that the part # on it is 911.613.111.10 which is a RoW part, rather than the .08 for NA. I'm not sure what the difference is as they appear the same

I'll keep you posted on what the part looks like when it arrives. Oh, and regarding that cover plate for the hole, I tried ordering part 901.504.747.00 "cover" from our host, but it came back NLA.

btw, here is what my ventilation system with A/C looked like before I started this project. I'll post pictures of the procedure I went through to convert it once I figure it out! .

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Old 01-12-2008, 08:17 AM
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Frank,

I never run my ventilation with the controls as shown in your red box. The flow-through ventilation is too warm in hot weather to do any good, and the fan is too noisy anyway, so it ends up getting used for fresh air in the winter, when heating the car through the lower vents. in this case, I prefer to direct the air through the dash vents, as it spreads it over a wider area, which makes it more comfortable and it helps keep the windshield free from fogging, which can be a problem. I suppose there is a little more flexibilty with this setup; I just don't use it.

If the duct you bought doesn't come with the levers and rods, that stuff could be made from scratch.

By the way, either of the two systems works fine. You can't really tell any difference in the flow between one and the other. The one in the brown car is all Porsche OEM stuff, too.

JR
Old 01-12-2008, 08:28 AM
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Great work so far. Keep us alerted.
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Old 01-12-2008, 10:02 AM
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Anybody got an extra tee that goes to the center vent they want to get rid of?
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Old 01-12-2008, 11:13 AM
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I know I'm digging up an old thread here but it's relevant to what I am trying to do.

I have a ROW (UK - RHD) 1983 SC that came with A/C. I have since removed it and am now doing a trunk (or boot to us Aussie's) resto. When I put it all back together I wanted to utilise the center dash vent. I know that I can simply add a 't' adapter from the fresh air blower but I thought it would be good to have heat from this vent as well. PP member makaio said he had done this but I couldn't find info on it.

I'd like to get some feedback from people who have done this. I figured I could tap into the left hand dash vent but it seems I would not get much air flow as I am splitting a small vent. It would also give me different air flow at each side vent.

Another option is to split both the left and right then combine back into the centre vent, although this seems a bit messy plus may not help air flow.

Another option I had considered was trying to set up a blower/fan in the footwell where the evaporator used to be. I am backdating the heat so could possibly use the rear blower in that position to feed only the center vent. The A/C fan dial could control this. I'd also have to make something that switches between fresh and warm air. I'd much rather grab fresh air from the front that via the heat exchanger, even with the valves open. A more complicated solution maybe, but it could work. Would also give me much more air flow.

As mentioned earlier an easy solution is to feed only fresh air into the center dashvent but the thought of heat from there is tempting.

I'd love to see pics of what has been done.

The following diagram grabbed from this thread best describes my setup. I don't have part number 20 that divert fresh air to the vent.
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Old 06-01-2011, 03:35 PM
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Part help please

Can someone help me with the part number for this T piece?

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Old 01-20-2012, 11:23 AM
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Vinny,
I could be wrong, but I don't believe the T-section you circled in the picture is an OEM part - at least I have only seen the splitter type part listed as #20 in the parts diagram (and shown in the white RoW car from Javadog). Besides, I don't think much air would actually make it to the center vent with that type of T setup.
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Old 01-20-2012, 09:26 PM
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Thanks Frank
I have parts 20 and 21 on order but theyre on the slow boat from Germany...
Thank you for starting this thread.
When you received part #20 did it come with the short bent linkage piece? I dont see a seperate part # for it.

thanks again
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Old 01-21-2012, 08:23 AM
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I can't remeber exactly how the routing went when I did this almost 10 years ago. But I do remeber I used a 1.5" ABS plastic sweep type tee to help with air flow vs. a standard tee with sharp 90 degree corners. I also upgraded the tubing with some vinyl type hose I picked up at a tractor trailer store. This allowed me to have fresh air out the center vent where after removing my non functioning a/c. I use to have pictures of it on my old computer but they were lost when it crashed. The car has been gone for almost 7 years and I have no idea what ended up happening to it after I sold it to a guy from Oregon.
Old 01-21-2012, 03:39 PM
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Vinny,

First, allow me revise my previous comment. Going back and re-reading this thread (I can't believe it's been 4 years), I see that Javadog stated that the brown car setup is OEM as well. Sorry for any confusion there. I have not looked at later years in PET to see if that T-part shows up.

Regarding your question, no part #20 did not come with the short linkage piece - I plan to fabricate that as I do not see this as a separate part either. The slightly more challenging part (for me) is attaching the rod to the existing lever. From Javadog's picture, it appears that the additional linkage attaches to the same fixing bolt as the control wire. But this bolt on my setup is only for the wire, and won't accommodate the linkage as well. I don't know if Javadog is still following this thread, but getting a closeup picture of how the linkage for part #20 attaches to the lever (red box #2 in my post on Jan 10, 2008) would be really helpful.

btw, in case you haven't figured it out by now, I'm embarrassed to say that I have not finished this project yet. I could not stop myself from unbolting basically everything from the car and restoring it. I am getting ready to put the fenders back on the car, but getting time to work on it has been difficult due to other commitments. I will post pictures of the completed setup when I put the ventilation system back in the car.

In case anyone is interested, I snapped a photo of what part #20 (911 571 039 00) looks like with the valve "open" (top left dash lever to the right). As suspected, the duct to the center dash vent is not completely closed off, and as you can see in picture, some air is still allowed to reach the center vents.




And a side view of the same part:

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Old 01-21-2012, 07:12 PM
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Thanks for the photos Frank

I think I may have found the T piece from the brown car in the longhood catalog.
Part # 90157206500

In any case, since I already have the part #20 on order, I will likely use it. Thanks for the pictures, I will share my solution for the bent linkage rod and it's connection to the housing linkage when I do this.

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Old 01-22-2012, 11:11 AM
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Vinny,

Ah, I see - that T-fitting looks like it is for use with the Webasto heater option, as (later) long-hoods used an under-dash A/C system. And the duct coming into the T is an input to the system (carrying hot air from the gas heater), not an output. There is a splitter (part #43 in your diagram) that splits the heater air to the left & right sides.

Thanks for finding the diagram - If my assumptions are correct, then that's one more mystery solved.
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Old 01-22-2012, 03:57 PM
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