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

1988 FORD E-SERIES VAN
18,000 MILES • V8 • 2WD • AUTOMATIC
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JEFF@THEDIAMONDLINE
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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
Mar 31, 2009 at 3:57 PM
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DOCFIXIT
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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.
Apr 1, 2009 at 12:05 PM
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JEFF@THEDIAMONDLINE
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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.
Apr 1, 2009 at 12:18 PM
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DOCFIXIT
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You can use any generic check valve a parts house should have.
Apr 1, 2009 at 12:41 PM
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JEFF@THEDIAMONDLINE
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Got it. I will post my results.
Thanks
Jeff
Apr 1, 2009 at 1:02 PM
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JEFF@THEDIAMONDLINE
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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!
Jul 29, 2009 at 3:50 PM
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DOCFIXIT
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Good job like the soilder gun to melt together. Good ol American nohow
Jul 29, 2009 at 4:13 PM