I have a 2001 Ford E350 van w/5.4L that when driving the A/C will switch from the panel to the dash. When I let off the accelerator for a little bit it then switches back to the panel vents. I assume that there is a vacuum leak somewhere but I am not sure where to look for sure. Any suggestions on where to check first or likely problems? I did check right behind the selector switches but didn't really find anything. Sounds like there might be a leak back behind in the dash possibly though. Thanks.

 

You definitely have a leaking vacuum issue---these are symptoms of that. Check here too:



It could also be your check valve, here's a diagram that might be helpful:



If none of these uncover an issue begin tracing each vacuum line looking for cracks and loose fittings. Occasionally the vacuum motor will develop a leak in its diaphragm too.

I'm hoping its not your check valve----hear they're tough to locate and change on our E Vans!

HTH

 

Definetly a vacuum leak. You can simulate the same conditions on the road by running the engine allowing it to build vacuum, shut the engine off and turning the key back on with the blower motor running, the dash air should remain blowing out the a/c vents, if you have a leak it will eventually divert to defrost the default setting. [no vacuum]. You can try running the a/c in both normal and max air. Running in normal position pretty much eliminates the recirculation or max air door circuit. The recirculation or max air door only closes in max position. Door at passenger foot well. Secondly the most probable vacuum leak area is at the vacuum resevoir, check valve and hoses mounted directly below the evaporator housing under the hood, Vacuum resevoir and the hose that attaches is a real commom failure. There is a vacuum quick disconnect at the passenger foot well, follow the hose coming thru the firewall up the inside plenum, you can attach a vacuum gauge to the connection and test the vacuum supply, resevoir and lines. Attach the gauge, start engine 30 secs, shut down you should pull and hold a good vacuum. If it pulls a good vacuum and leaks down the leak is on the down side of the check valve. The evaporator housing under the hood is pretty difficult to remove. Its the only way to gain access to the resevoir and ck valve. If thats the case you might consider installing a remote mounted resevoir and ck. valve and replumb.

 

I also have the same problem and tried your simulation and it went to the default defrost vents within about 30 seconds in both max and reg a/c.
I looked around the passenger foot area and I see a white and black hose. The black one goes out the firewall and cannot locate it, or the vacuum resorvoire.
Anyone got a diagram?
TN is 100 degrees this week and the 7 kids want daddy to fix the a/c.
Trying to be a hero.
Thanks

 

JWA, can you repost or PM me these videos/links? They aren''t showing up. I think this may be my problem as well as I have strong cold air from my rear air, but something going on up front. Thanks
Oh, I posted about my problem, it's 8 or 10 posts down if you don't mind taking a look.
thanks
eric