1988 Ford E-Series Van Possible vacuum leak in AC control c

JEFF

MEMBER
1988 FORD E-SERIES VAN
V8
2WD
AUTOMATIC
18,000 MILES

I'm trying to sort out a bug on my RV. On a 1988 Ford E350 chassis with a 460, I have a problem with the cab A/C blowing thru the vents on the dash at idle or high vacuum, but when pulling a grade or accelerating/low vacuum the dash vents close and the cold air goes elsewhere. I sorta know the following.
The system is operated by vacuum.
There is a leak somewhere.
The check valves in the lines seem to be working/flow in one direction.

The question is, is there a generic problem to this system that should be checked first? I am trying not to pull everything apart for no reason and the E350 van is packaged pretty tight under the hood. My Clymer book has no clues. Any ideas?
Thanks
Jeff

6 Replies

DOCFIXIT

MECHANIC
18,828 POSTS

Sounds like a classic check valve there maybe one you missed. RV can be a pain you never know how system is laid out. Also see if you have a vacuum resivor and check to see if it holds vac.

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Wednesday, April 1st, 2009 AT 12:05 PM

JEFF

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4 POSTS

Thank you for the reply. I went to Ford dealer for replacement check valves and they are not longer made. I don't know if this is a standard check valve (one way only) or if it has a specific rate bleed-off. And there are a few in the system-I was just going to change them all. Will check the tank and lines, too.
Thanks again.

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Wednesday, April 1st, 2009 AT 12:18 PM

DOCFIXIT

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You can use any generic check valve a parts house should have.

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Wednesday, April 1st, 2009 AT 12:41 PM

JEFF

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Got it. I will post my results.
Thanks
Jeff

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Wednesday, April 1st, 2009 AT 1:02 PM

JEFF

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4 POSTS

Finally had the time to dig in and find the problem. It was the vacuum reservoir. It is a plastic ball, about the size of a softball and it had split at the seam in the middle. Melted it back together with a soldering iron and the vents hold their position even with the engine off.
This also tells me the check valves are working too.
I will keep my eyes open for a new one, but in the meantime, I have A/C going up hills. Thanks!