Posted this here but if it should be moved or would be helpful posted in another sub-forum as well please advise. Onward........
Soooooooo most anyone with an E-Series where the heater air flow has needed repair too often it comes down to dealing with the vacuum reservoir and check valve so important to proper operation. The problem has always been WTF is it exactly? You can look nearly everywhere, you know its somewhere but yet its never found---until now.
My van is undergoing an engine swap so there's no better time looking for that elusive POS---sadly this is just about the only way to find and partially see this part. Even more sad is in order to R&R the existing part would require disassembling nearly the entire A/C Heating system including properly recovering the refrigerant. So without further adieu here's that F'n thing caught in its natural habitat, naked and exposed:
Inside the yellow box:
Zoomed in towards the back of the evaporator box near the metal firewall; pay attention to the yellow and red arrows:
Another view of the evaporator case, additional info:
The greenish lines show two gussets formed into the evaporator case---the reservoir is partially obscured by these which just adds to it being so difficult to see or find.
This is what we've been searching for, uninstalled of course:
The yellow arrow above relates to the yellow arrow in the second photo---they're pointing to the same portion of the vacuum reservoir. Note: The blue-green arrow points to what appears to be a bolt hole but its not---seems to be a flange that snaps into mating prongs on the evaporator case instead of using a threaded fastener.
The red arrow in photo #2 relates to this part, inner evaporator case:
That projection fits into the interior side of the evaporator case exiting outside the firewall--its the A/C condensate drain, this view:
Another view of the uninstalled reservoir:
The upturned flange on the opposite side ^^^ cannot be seen or felt by hand how its attached--guessing the same sort of snap-in-place fastener.
This one shows simulated vacuum tubing installed, the Ford check valve installed in what I believe would be similar to the factory installation:
Black to intake manifold, purple to dash mounted A/C system controller aka Function Control (Heat, Vent, Defrost etc)
Hopefully this shows how nearly impossible it is to access this part---it would require a complete disassembly of the A/C-Heater system inside the engine bay. I hate bashing Ford but WTF where they thinking with this idea? Did GM or Chrysler trick them into this design? I simply do not see any way possible to R&R this part any other way.
There have been a few great threads of improvised and self-fabricated vacuum reservoirs. For me its far easier buying the Ford parts and install them inside the cabin tucked up under the dashboard. Removing a few lower dashboard trim parts there's plenty of room for all this to fit neatly, cable ties holding it in place. I'll be doing that on the van shown and will probably post a different thread how that'll be done and the finished results.
I hope this is informative---I've been searching for this damn thing nigh on 10 years or so.