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Old 01-25-2019, 09:30 PM   #61
zimmej51
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Defrost duct installation

I carefully removed the foam residue from around the defrost vent. Fabricated some "mount plates" using .0625 ABS sheet. On the bottom of the plates, I left a gap so that the blind nuts would not interfere with the mounting of the plates.






By the way, this is the ABS adhesive I used. None of the Home Depot stores in my area stock it for some reason. But Ace Hardware does. You can also get it at a plumbing supply. It's black and pretty thick. Drys quickly to a hard, shiny bead. Looks like the adhesive used by VA.



This is where the VA supplied defrost duct needs to go. The 74-76 Corvettes have a 2 piece dashboard with mounts for the holes on each end of the duct. But the 77-80 do not have any kind of attachment for the duct. That's why I made the mount plates above.




Trimmed away the foam from the area where the mount plates need to go.



Roughed up the surface where the mount plates will go.



After measuring carefully, I cemented the mounting plates onto the dashboard. Used some self adhesive weatherstrip foam to seal up the defrost duct. Then I placed the duct on the studs and gently tightened up the nuts on each end. BTW I recommend attaching the flexible hose to the defrost duct while it is out in the open. It was a real bear to get the hose on. It won't be slipping off any time soon!


I put the dashboard back in place once again for a clearance check, all is good. This completes the defrost duct installation.
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Old 01-25-2019, 09:57 PM   #62
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Passenger side dashboard vent

The passenger side vent has a lot more room around it, but it still needs to be as short as possible. I re-purposed a mounting flange. The flange has a round opening with "nubs" to retain the flexible hose. So first, I shortened the OEM vent frame.



This is the adapter flange that came with the kit. I won't be using the outer part of the VA adapter.



I set the shortened OEM vent frame onto the adapter flange making sure it was centered. Then I applied the ABS glue to the inside of the frame using a long Q-tip. It flowed out very nicely. It dries to a hard, shiny, black bead. I tried to take a picture of it but managed to get it out of focus. It does look exactly like the glue joints from VA. After the assembly has fully cured (overnight) I will remove the excess material from the flange. The pics show the assy before I removed the excess material.









To get the flexible hose from the evap case over to the passenger side vent, VA supplied a pass through ABS duct. This duct has sort of a flattened rectangle cross section. It's purpose is to go behind the center dash instrument panel. Then another length of flexible hose connects from the pass through duct to the passenger side vent. After confirming the best location for the duct, I marked the location and then removed the dashboard again. I made 2 brackets out of 1" aluminum band material and used my Marson thread setter to install a couple of 10-32 rivet nuts.



That will pretty much complete the passenger side dashboard vent.







Next will be the two center dash vents. These look to be pretty easy, the adapter for the vents is pretty close to what is needed with only a few minor mods. At last, I'm beginning to see some light at the end of this HVAC tunnel!!
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Old 01-25-2019, 11:41 PM   #63
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Suggestion on the defroster hose.

I know how tight it is as I have a VA system in mine. You would think that would be permanent. Those plastic ducts loose there stretch and relax pretty quickly. Then they get heated up with warm air and expand, then you turn the blower on high.....

A couple of sheet metal screws to hold the duct on there is cheap insurance.
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Old 01-26-2019, 06:15 PM   #64
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Good idea 7TRoadster. You're right, those flexible hoses were ^#$%! hard to get on the ducts! I never would have guessed they could stretch and come loose, but it wouldn't surprise me. I will do as you suggest, can't hurt a thing. Ran into a bit of a problem with the 2 center vents, the one on the passenger side in particular. The defrost duct gets in the way of the hose going to that vent. I was going to have to do some fabrication on that connection anyway, but the defrost duct complicates it some what. Was tired of messing with it this evening, will have to go out and stare at it some more tomorrow.
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Old 01-27-2019, 06:36 PM   #65
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Center AC vents

Well I jinxed the whole thing when I said the center vents in the dash looked like they would be easy. Guess again! The defrost vent is in the way and running the passenger side flexible duct up high like I had it takes up room needed for the center vent ducts. That part wasn't hard to fix, but I'm debating which would be easier. Making my own center vent duct from scratch allowing some space for the defrost duct, or modifying the defrost duct. Will take another look at it tomorrow.
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Old 01-28-2019, 07:49 PM   #66
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Dashboard Center Vent Duct

Ok, wasted most of the morning looking at every possible way to jury rig the components I have in order to connect the 2 dashboard center vents, clear the defrost vent, etc. Finally I threw in the towel and decided to build my own duct from scratch. Should have done that to begin with. Here's the basic plug, I will probably make it in 3 pieces; the top half, the bottom half, and the rear cap with the 2 oval connectors.



I won't cut the plug up until I decide if I'm going to cast them with West Systems epoxy and glass/carbon, or if I'm going to use ABS and a vacuum former. I'm much more familiar with the process to make epoxy/glass parts since I've built and flown RC airplanes all my life. Lots of experience with fiberglass and carbon fuselages. It is much more accurate since you don't have to allow for the media having inconsistent thickness due to stretching in the mold. The downside is that it is messy and slow, not well suited to making any kind of production run.



I have done very little vacuum forming, and would have to construct a small vacuum table for this project. The upside is that once that is done it is very easy and quick to make multiple copies.


I tried to get a picture with the plug installed in the dashboard but it was too confined and I couldn't get a good one. The relief on one end is to clear the defrost duct. It now has about 3/8" clearance at it's closest point to the defrost duct. There is plenty of room behind the oval duct connectors. I cut the back at a 5° angle to help direct additional air to the right vent and also to help with connecting the flexible ducts.



I designed this using the 2" VA flexible ducts instead of the 2-1/2" flexible ducts. VA has reducers to go from 2-1/2" to 2". I believe the 2" will be more than enough for the center vents, especially since the run from the evap box to the center vents is only about 8" to 10".












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Old 01-29-2019, 05:55 AM   #67
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Where did you get your foam for making the plug?
For years I had 2 x 6 ft slabs of foam from a surfboard shop, finally used it all up in one way or another.
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Old 01-29-2019, 06:40 PM   #68
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slofut it's not foam, it's balsa. I had a couple of large chunks laying around in the RC airplane shop. I've had better luck with it than with foam. You can work it with standard wood shop tools.
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Old 02-22-2019, 09:10 PM   #69
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Vintage Air center AC vents custom duct

Back in the saddle again, been almost a month! As noted in the previous posts, I have just about everything test fitted inside the car but had ran into a big problem with the 2 AC vents in the upper center of the dashboard. I wasn't able to use/modify anything in the 74-76 VA kit to connect the vents to the evap box. I couldn't think of any solution other than to make my own duct.


So I spent some time making this vacuum former. The box on the right is the heat box, I wound a nichrome wire coil and mounted it in the bottom of the box. The rest is pretty much self-explanatory. I won't post all the construction details since this is a Corvette forum, but if anyone's interested I'd be happy to share what I learned about vacuum forming, both successes and failures.





I used the VA defrost duct that came in the kit, but had to make some custom mounts for it. Details are in the previous posts. The biggest problem with the center vents is interference with the defrost duct. I carved the forms (called "bucks" in the vacuum forming world) out of balsa wood. They are pictured in previous posts. The bucks in the picture wound up being a little different, primarily because I decided to make the rear of the duct (where the flex hoses connect) a separate piece. So I wound up forming 3 pieces that make up the finished duct buck. I had 3 different bucks but didn't post the pics.



The process went smoothly for the most part, my first adventure into vacuum forming. I used 3/32" ABS, smooth on one side and a texture on the other side called "haircell". After the three pieces were formed I trimmed them up and assembled the duct using the black ABS cement used in plumbing. The two "nipples" are sized to fit the VA 2" flex hoses. The evap unit has two 2-1/2" output nipples, VA makes an adapter to connect a 2" flex hose to a 2-1/2" hose. I used the 2" because of the limited space. I'm pretty sure it will flow enough air. So here's what it looks like:










And this is how it fits onto the center gauge bezel.











Tomorrow I'll do a final fit in the dashboard to be sure I didn't miss something.The bucks I have can be used again, the process doesn't hurt them, so I might be persuaded to make a couple more of these ducts should someone be interested.


More to come...
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Old 03-02-2019, 10:03 PM   #70
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Vintage Air duct work, 81 C3

Ok, I think I've got it. I have test fitted all of the modified ducts under the dashboard.


I should point out that in previous posts I had positioned the duct to the passenger side AV vent up high with a couple of fabricated brackets. It turns out that wasn't a good place to put the duct. It's a crowded area just above the VA evap box. Plus, the duct completely wiped out any possibility of a small glove box. Lastly, the duct up that high went right in front of the ECM connector on the evap box. Time for plan B.


I decided to try the "low" road, running the duct just behind the lower edge of the dashboard. It looked feasible, so I fabbed up a mounting bracket using the two rivet nuts I had already placed in the crossover duct.





The bracket is in place, minus the duct. The red lines are just marks I used to position the bends.





Bracket mounted to the crossover duct...





And mounted to the evap box...





Dashboard in, flexible hoses connected...





Here's a tip. If you are repeatedly taking out and putting in the dashboard, loosen these 2 screws that hold the spring clips in place. This will reduce the strain on the dash from repeated installing/removing.





Defrost duct connected...





This is really hard to get a picture of, but this is the backside of the custom made duct and the 2 ports on the evap box. I didn't show it, but the center bezel with the new duct mounted fits easily. That means the new duct can be more or less permanently mounted.





Another shot of the new duct and the evap box connections. They aren't hooked up yet because I used 2" hose and the evap box connections are 2-1/2". VA makes reducers to connect the two different sizes.





Front view of the center bezel...





As you can see, the previous owner had hacked a DIN opening in the center bezel for a radio upgrade. There is at least 7" of depth clearance, the hose can be pushed further back if necessary. It could be close, depending on what radio you use. I'm pretty sure the factory radio will NOT fit. That thing is huge. My plan is to replace it (and the center bezel) with a modern radio that has knobs and resembles the original. However I don't want a CD drive, or tape in the unit. Plan to use bluetooth or usb.






Here's another really tough shot. This is where I put the relief in the new duct to clear the defrost hose. It looks like they are hitting in the picture but they actually aren't.





The simplest of things can sometimes turn into a real %$#&^!. The VA fittings have a really neat "nub" on the connectors that the hoses slide over and are captured. It looks like they just heated up a 1/8" rod and pushed it up through the fitting to make the nub. But I can guarantee you that isn't how they did it! ABS is some weird stuff, it doesn't just get soft so you can manipulate it into a shape. When it softens enough for molding, it has to be clamped in some sort of frame or it just collapses in on itself. I made 3 different tools to try to duplicate the nubs that VA does but had zero success. I'm pretty sure they have some kind of form fitting device to "convince" the ABS to conform to the shape of the nub. In any case, after wasting almost an entire day, I just made some nubs out of scrap plastic and glued them on the duct. Tried to pry one off and it wouldn't budge.





Couple of things that maybe didn't show up in the pics. The new duct that passes under the steering column looks lower than the factory one. But it isn't, believe it or not. I compared and measured both of them, there isn't a significant difference.



I didn't hook up the passenger side vent in these pics, but there is plenty of room.


With this configuration I believe I can modify the glove box insert, or make a new one, and have a glove box. Won't be big, probably just big enough for, well, a pair of gloves!


The evap box in the pics does hang down a bit, but it cannot be mounted any higher. I was kind of worried about it but had a tall friend "test sit" in the passenger seat. It was no problem. The pics tend to make it look a little lower than it actually is.



One last shot of the duct routing minus the dashboard.


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Old 03-03-2019, 07:27 AM   #71
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Wow Zimmie, that's awesome fab work. I'm amazed you built the vacuum forming tools to make that duct, and it looks factory. May want to ask VA if they need a few of those, or make some to sell as I'm sure you're not the only one to deal with this (I'm sure this has crossed your mind). I hope Richard454 sees this, he would be impressed too.

Keep up the fantastic work and updates.
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Old 03-03-2019, 07:10 PM   #72
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Thanks Slofut - I plan to be hitting the project hard and heavy, spring isn't that far away! Learning a LOT about vacuum forming, not as straight forward as I thought it was. Guess I was thinking of that Vacu-form toy I had when I was a kid!
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Old 03-04-2019, 06:18 AM   #73
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Quote:
Originally Posted by zimmej51 View Post
Thanks Slofut - I plan to be hitting the project hard and heavy, spring isn't that far away! Learning a LOT about vacuum forming, not as straight forward as I thought it was. Guess I was thinking of that Vacu-form toy I had when I was a kid!
I had one of those too! By Mattel I think, and it worked too.
I remember it got really hot. Hell, they won't let kids have something like that now... I mean after you get burned once you learn how to not get burned again right?
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Old 03-04-2019, 05:02 PM   #74
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That is a ton of work to get things squared away. For my 77 thinking start with the bare A.C./heat unit and build from there using factory duct work as much as possible. Anyone have a solid shot of how far the unit sits below the dash with a focus on the foot well?
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96 stock and 86E I don't even know how to explain anymore.
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Old 03-04-2019, 07:30 PM   #75
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Use stock AC ducts

Quote:
Originally Posted by C4forlife View Post
That is a ton of work to get things squared away. For my 77 thinking start with the bare A.C./heat unit and build from there using factory duct work as much as possible. Anyone have a solid shot of how far the unit sits below the dash with a focus on the foot well?

You're right about the extra work for sure! But like so many things the first one is the hard one. The first one took weeks and weeks but I probably could do a second one in a day or two! The worst thing I ran into was that center vent thing. That's why I was wanting get it nailed down. It would be a big help for anyone doing a similar install. If I can get it figured out I'll make a few of them in case somebody wants one. That's the great thing about this forum, learning from the experience of others. Reminds me of something I once read, "Learn from other peoples mistakes. You won't live long enough to make them all yourself!".


My original intent was to try to use the factory ducts like you said. But once I got into it that idea quickly fell apart. They aren't ducts like I envisioned, they are more like structural members that happen to conduct air. The "keystone" is that big chunk at the center bottom where the floor heat exits. Just about everything else is either plugged in or physically attached to that center thing. That's why the defrost is such a problem. The factory duct is supported by that center box thing, not the dashboard itself like the pre 77's. But, maybe there is a way. If you can get it figured out please post. If it's possible, sure would make things easier. I may post a pic of all the factory ducts, assembled and taped together. Seeing that out in the open might give someone some ideas.


Tomorrow I'll get some pics and dimensions of the evap box relative to the floor and firewall. There is no question that it hangs down a little lower than I'd like, and I was worried about that. That's why I put the passenger seat in and had a couple of friends test it out. They didn't feel like it would be a problem. Hope they are right!!
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