Rebuilding / Improving the HVAC housing

[Diametric]

Hi friends!

I'm working on a 1999 Dodge Grand Caravan which I love dearly and consider a family member. She's been with me a long time and brought me safely home many times from far away road trips.

So I'm in the process of changing out the Evaporator Core and while in there, I decided to pressure test , inspect and evaluate the Heater Core and the new Evap Core and then test the blend door actuators, temp sensor and insulation. I also replaced the blower fan motor which most likely is the factory original and 27 years old. It was beginning to occasionally make that loud howling noise that comes from worn, dry bearings I believe.

One of the more difficult tasks I'm facing is that the HVAC housing was manufactured with custom molded styrofoan insulation pieces in the bottom of the evap housing that have become brittle, dry rotted and basically are falling apart. I want to re-insulate that area but getting replacement styrofoam pieces is out of the question. Below is a photo of the failing styrofoam.

My first thought is to replace the strofoam with an improved coating of some sort. The housing is plastic so just about any coating would probably stick. Something that can survive hard cold and lots of time in a moist environment. There are too many compound curves to shape anything (as far as I know). There's got to be some brush on insulation coating that could be applied easily that would stick well and endure the conditions inside a plastic HVAC housing for a long time (10-15 years minimum?)

If I had to go with a sheet of something, Adhesive backed Neoprene comes to mind but I'm not sure if that would stay stuck.
It has to be NON-Expanding foam or at least limited to approx 1/8 expansion.

Anyone know of a product for just this use or have any suggestions?

Styrofoam_in_HVAC_IMG_20260827_213322321.jpg (133.73 KiB) Viewed 712 times

[JohnHere]

Option 1: I've never tried either option, but how about spray-on foam-in-a-can, the inexpensive type from your local home center that's designed specifically for sealing around windows? Unlike expanding foam that will fill gaps one inch or wider, the window variety features minimal to no expansion, but I'm unsure how it would stand up to moisture. I would go to the store and read the label carefully, or contact the company directly.

Option 2: PUR Black Foam (BF01) is used in Water Gardens and Water Features, so I know it's waterproof. However, I'm unsure how it would work for your application. It's fairly expensive last I checked, and it requires a Pageris Gun (sold separately) to apply the foam. Unlike Option 1, I believe it's the expanding type of foam.

Other than those, I'm not aware of any other products that might be suitable.