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Don, there is no separate heater plenum with factory AC. Heat enters the AC evaporator box and depending on how a flapper door is directed by the regular heat/defroster select knob on the heater portion of the instrument panel vent control area it goes to a single defrost outlet or in full heat position, circulates freely thru the box containing the evaporator core. If the knob is positioned midway heated air will go to both.

With heated air in the box, if the dash vents are opened heat will come out just like the chilled air. Since the heater blower is not as large as the AC blower air flow is not as much as with AC. To take the place of the old heater plenum there is a slot in the box bottom and over the slot a door that opens or closes to regulate air flow. The door is operated by a push/pull knob on a shaft located at the center of the pushed out section of the box just under the glovebox. For heat you would normally opens the door and for AC you would close it but the door can be partially open so heated or chilled air can go to both the dash vents and to the floor outlet.

Howard, I was thinking along those same lines that they were for controlling the directions as they do swivel. There was very little material left on them when I started removing them. I have no idea what they looked like,

Don, The back side was similar to cardboard but it isn't cardboard. If I had to guess I would say it was a thin piece of masonite. It is very "fiber- ish". The front (main casing) is something more sturdy than that. It is almost like bakelite but not bakelite. Sorry, I cant be more specific.

I think the front of the plenum is molded fiberglass or resin material and the back is the high density water resistant or asphalt impregnated cardboard often used in door panels. Not sure what kind of material was inside for the separator but it did not seem to hold up -- at least the cardboard part connected to the heat/defrost diverter did not.

Howard, I know there wasn’t a separate heater plenum on A/C cars. It was the A/C plenum that I was talking about and where to get it reproduced. I have two but each has flaws and faults of one sort or another.

No place I know of repros them and aside from the ducts it is made entirely of sheet metal. Possibly you could take an old one to a sheet metal shop and tell them what you want and have it repaired or another built. When I did my conversion I built my entire assy ducts and all from scratch to fit the modern component needs but keep the original look.

The only part on my repro that needs more work is the actual visible dash ducts because commonly available modern casting materials are not able to withstand high interior temperatures such as after sitting in the sun. Without pressure casting abilities better than what I had the stuff that will withstand the high temps is not easily cast with gravity alone.

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Yes, I am aware they are not reproduced. I was looking for a source to make a one-off or maybe two-off using mine as templates and for the hardware.

But sheetmetal? Mine both seem to be made of the same type of board that the heater plenum was made of. You have me wondering now if I looked at them carefully enough!

Believe me, mine at least was all metal and fairly heavy gauge but the cases are covered on the outside with a cemented on thin black insulating foam rubber material. I was able to find an almost exact match to the insulating stuff at McMaster.

Here is a view of the heat/defrost flapper area where you get a good view of some of the sheetmetal and joint construction.

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Does this help…. You are missing part of the backing. And I’m missing the little brackets.

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Yes Henry, that does help.
It is not a pivoting directional thing at all. Its just a flap that narrows the opening. That is much easier to duplicate. Thank you.

I pulled these 2 defroster ducts off the shelf today. These are too brittle to reuse. I was planning to simply make a pair using sheets of EVA Foam.

After a little research, I am afraid that the heat might be too much for EVA foam. It only takes about 80 to 90 degrees to shape it. The heat coming out of the heater core might deform them.

Anyone any suggestions from my support group?

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