1993 F250 HVAC System Vacuum Issue
 

Howdy Gents
I have a vacuum leak in my HVAC system. Vent selector wasn't working, traced the problem to the black vacuum hose in this image. It goes into the AC coil housing, and to where? Its leaking, as when I plug the end of that hose, the selector works fine. Can't find any intel anywhere on where that male fitting on the housing leads to, but when I connect the black hose to it, and blow in, I can hear the air inside.
Anyone?
Thanks gents.

https://cimg4.ibsrv.net/gimg/www.f15...c4c2e5a3ab.jpg

Spent some more time on it and the plastic "box" that tube attaches to is the vacuum reservoir. On the Ford parts schematic it appears to be a separate chamber from the HVAC plenum. Blowing into it via the hose results in air going in but no pressurization of the reservoir, indicating its escaping to somewhere. Anyone ever come across this. Im assuming the reservoir is a sealed unit, right

Guess it gets a touch warm down there. Now I know why the reservoir isn't holding vacuum. 93 F250, 7.5 with 45000 miles.

https://cimg9.ibsrv.net/gimg/www.f15...94fec8a49f.jpg

Click this & read the caption:

https://www.supermotors.net/getfile/...il/evapins.jpg

Thanks for that link.
Strangely, the original insulation was in place and in good condition. I'll be using heat reflective foil tape as well as the insulation when I re-install.

Do you have an aftermarket downpipe from the turbo? Are you overboosting, or doing anything else that would raise the downpipe temperature?

It's a 7.5 gasser. Stock exhaust manifolds. Passenger side 7.5 exhaust tends to run hotter, but still...

Sorry - somehow, I was seeing 7.3 there.

No, the R manifold shouldn't be hotter than the L, but it is much closer to that plastic than anything similar on the L side. I'd add a thin sheet-Aluminum heat shield to the box, and maybe a galvanized steel one above the manifold.

Many thanks for the input Steve.
The website you linked doesn't appear to stock that party any longer. Im guessing Ill be relegated to hitting junk yards and auto recyclers for a new housing. FoMoCo no longer has the part either.
Gotta love old Iron.

The site I linked is just an image host - it doesn't sell parts, but I do occasionally. That one is just something I cut out of a sheet of insulation, though, so you could do the same thing. If you're looking for the reservoir; yes, get it at the JY.