Ive got a 92 E150 Conversion van with 5.0L and E4OD (I think). Latley Ive noticed that when I accelerate, the air output from teh dash vents diminish and switch to the floor vents, then none at all. THen when I resume my cruse, the cycle reverses itself till It's back to comming out the dash vents. I know the controls are vacume operated and my manual referances a check valve for the enviromental controls. This all makes sense to me as the vacume does drop as I acelerate and return when I cruse.

My Question is, Where is this valve located? My manual does not specify it's location and as of yet, Ive not been able to locate it. Any tips or info would be greatly appreciated.

George

 

Start by studying the vacuum diagram located under the hood. There should be a reference to the check valve if it is under the hood area.Even it is under the dash,you will still see the initials "HVAC" pointing to a vacuum line on the decal.While studying the vacuum diagram,take note of the accesories that share the same branch as your "HVAC".Verify that these lines are not pinched,melted shut,etc. and are hooked up coorectly.Like I suggested,check out the whole vacuum circuit before you go to far.
Phillip

 

Ive done that. The diagram under the hood is not much better than what's in my manual. All teh lines look to be in good shape w/o any chaffing of melting. I just need to find out where the check valve is located and I can do the diagnostics from there.

 

The check valve in in th vacuume storage tank. It may be a metal type juice can and may be rotted out. It can be replaced by a plastic type. Also any leak downstream from this can in system will cause this problem. Hope this helps.

 

THanks for the input. One more question - Where is the vacume resivore located at? Ive seen a squairish plastic "container" located at the right front of the van with 2 VAC lines, red & black. Could this be it? I havent seen ay of the round metal cans (the Bean & Coffee can) like on my 79 Bronco.

Looks like it might be time to get some better manuals for this thing. It's a nightmare finding things under the hood!

 

That sqaure can you are looking at is probably the evaporative canister.It's job is to contain gasoline fumes while the vehicle is resting and while the vehicle is running it will direct the fumes to the intake for combustion with the air charge.Once again,you should see a referance to this canister as well as your HVAC{heat-vent-air condition}connections.Happy searching!!!
Phillip