HVAC Questions: Vacuum Actuators & Foam Insulation

[NickyV]

I’m working on restoring an HVAC box for my 87. Got two questions.

 

Vacuum Actuator:

The large actuator that came with my replacement box appears to be damaged, but I’m not 100% sure. It looks to be cracked around where the nipple meets the bell of the vacuum housing. Here is a picture.

 

 

I’m assuming this is not supposed to be like this, but I could see how this might be intentional — so that the door it controls needs constant vac to stay open and always closes when the truck is shut off.

 

If it’s broken, should I just seal it with bondo? Or do I need to find one that’s not broken?

 

Foam/Insulation:

Has anyone figured out improvements on the insulation inside the box?

 

It’s obvious that the foam around the ports and on the doors is intended to keep the box sealed and maybe prevent air whistling noises.

I think I can see why they used light weight, open cell foam on the doors and around seams. They wanted to keep the doors light weight and to have a lot of “squish” for tight seals.

 

But what is the purpose of using open cell foam on the inner walls of the box? It seems like this foam is primarily for temperature insulation. Although maybe it is also for sound dampening.

 

I am wondering if using something like DynaMat in a few key places might be better? I’m specifically referring to pieces like this one.

 

 

I asked AI and it said the open cell foam is better for this because it helps with wind noise. But it seems to me that this would not do much for temperature insulation.

[llhat]

if the actuator does not hold vacuum,    some JB weld instead of bondo ....    or replace it completely.

[eaglescout526]

Wait? Which actuator is it? I probably have a spare one. 

[NickyV]

@eaglescout526 It’s the bigest one. Kinda square edged. Looks like it was painted black.

[NickyV]

I’m gonna try some JB Weld now. See that works.

[ghetdjc320]

Any open cell foam will help with noise but noise isn’t much of a problem inside the box itself. When I rebuilt mine, I sealed all the junctions with permatex black and added 1/8 minicell foam for insulation only. In retrospect, a good option would have also been dynaliner in 1/8. You can add some open cell near th vents and duct exits to act as a baffle. But I find that stopping escaping air around the seams made the biggest difference in airflow and sound