Hello...I have a 2001 Ford V10 E450 running my class C and just this weekend we were driving and notice the fan for AC or Heat or vent will go from dash air to defrost when the motor is under stress like going up hill. If I let off the gas the air flow switches back to coming out the dash vents from defrost. I was looking around the internet and some have said this can be a Vacuum check valve located somewhere over the driver wheel well. Anyone have this problem before? How much is part?? How do you fix it?? Someone on the internet said you have to remove a ton of stuff to get to it and there are other methods of dealing with this problem. Motor runs fine no misses or anything just this issue. Thanks

Hi,My older class C had a small vacuum canister, it was about the size of a large softball, about 4" diameter. There must have been a check valve between the intake manifold and this canister, and then the vacuum controls on the A/C system. I never had a problem with the A/C changing to defrost while driving. If you can find the vacuum line going to the A/C controls, you already know that there is a check valve between the controls and engine (it might not be working though) you can install a vacuum canister in a tee to that line. You might also need to install a new check valve. You do not require to dfind hte factory one, just put it inline with the vacuum hose going towards the dash air controls. Napa should have a vacuum canister. Basically if you can fit it under the hood, it will work. You can even mount it remotely, and mount it under the RV (especially if it is metal) then run a 1/4" vacuum line to it. Good luck finding everything. Fred.

Its likely more than a bad check valve. You probably had one of the lines eaten by a critter.

Is there a set of plans for this system? I have been looking around..I'm going to have to try and do this myself being that the dealer will want a ton for this.

I had the same problem with my 2005 E450. Their is a RED plastic vacuum tube under the hood on the passenger side near the oil fill & the windshield washer fill. I installed a checkvalve($5.00 at Auotzone)between the red plastic tube and the black rubber hose it goes in to. Use a small zip tie to secure the checkvalve to the rubber hose. Worked for me.

Ok Ken did it today just need to try it out on a hill. Will let you know otherwise its off to the dreaded dealer. Thanks

2001 E450 SD Vacuum check valve?? | Good Sam Community

k9-keno
Explorer
May 15, 2014
Ok..Hope some people get in on this since I think I'm finally close to fixing this problem. So I found the main red vacuum line off the manifold and found the line on the passenger side where it comes in the firewall. If I take the red line off manifold and run it across right to the line that comes in from firewall and connect them am I bypassing anything I can't see?? Like a canister etch and if so will it hurt anything? Again still have ac and heat coming at dash fine at idle and normal driving if I stress motor like up hill ac or heat will default to defrost then come back to dash after stress is gone. Thanks
k9-keno
Explorer
Apr 03, 2014
Just wanted to see if anyone is having my original problem from this thread. I have tried everything but what grinder suggested since that might be to advanced for me. Hate to go to deal I know they will want a ton of money!!
grinder613
Explorer
Oct 02, 2013
On my 1999 E450 chassie a critter chewed on the plastic vacuum line at the intake manifold exit and the check valve was malfunctioning. The check valve and canister are buried behind the heater/ac on the pass side. To get at the valve you have to drain the ac and remove the components. I made it easier on mine. I rerouted the vacuum lines and repositioned the valve and canister behind the passenger lower dash panel. If you look on youtube, some guys cut a hole in the inner fender to get at the canister and valve. My method is easier.
ken0304
Explorer
Oct 02, 2013
Opps typo (2004 Ford E450).
ken0304
Explorer
Oct 02, 2013
Also check an old forum topic (2001 Ford E450).
ken0304
Explorer
Oct 02, 2013
The checkvalve is a one way valve, be sure you instaled it in the right direction. Otherwise there must be a vacum leak. The red plastic tube goes from the manifold connects to the black rubber hose, runs through the fender comes out under the dash passenger side, goes to the vacumn motors on top of dash,and to the dash slector switch. In the middel on top the dash is axcess panel to the vacumn motors. Check everyware you can for leaks. Good luck.
k9-keno
Explorer
Oct 01, 2013
Ken had no luck with that fixing it any other ideas before I have to go to the dealer???
k9-keno
Explorer
Sep 19, 2013
Ok Ken did it today just need to try it out on a hill. Will let you know otherwise its off to the dreaded dealer. Thanks
ken0304
Explorer
Sep 16, 2013
I had the same problem with my 2005 E450. Their is a RED plastic vacuum tube under the hood on the passenger side near the oil fill & the windshield washer fill. I installed a checkvalve($5.00 at Auotzone)between the red plastic tube and the black rubber hose it goes in to. Use a small zip tie to secure the checkvalve to the rubber hose. Worked for me.
k9-keno
Explorer
Sep 16, 2013
Is there a set of plans for this system? I have been looking around..I'm going to have to try and do this myself being that the dealer will want a ton for this.

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2001 E450 SD Vacuum check valve??

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