Heater air flow issue

I have a 2001 xj.
When I accelerate the air flow changes to the defroster and when I let off the gas it returns to the dash.
Could this be caused by a defective check valve?And if so where would I look for it?  

bkhjeep:
I have a 2001 xj.
When I accelerate the air flow changes to the defroster and when I let off the gas it returns to the dash.
Could this be caused by a defective check valve?And if so where would I look for it?

If you don't own or have access to mechanical diagrams
You could try this site; http://www.jeepsareus.com
Some of their diagrams really fit the bill for what
you need.

Good Luck hunting this Gremlin.

BoneShkr

The Trail Never Ends  

I have the very same problem. Its going to be a vacuum leak. Xj's vent systems are run entirely by vacuum. I have read it is usually the line coming from the vacuum canister in the front bumper.

I still need to fix mine too, especially before summer.  

Thanks for the info.I'll start there.  

Think I found the problem.The hard line from the cruise control was broken almost in half.
There is a check valve to the vacuum canister just off the manifold but it seemed to work fine.XJwheeler you may want to check that unless you know the canister is leaking.  

Appreciate it! Never thought to look at that, i'll be sure to check it out.  

I spoke to soon,The problem is still the same.
I pulled the reservoir and water tested it,all good.
Stumped!  

OK finally fixed.I got serious about it and what I found was that I had 13 lbs of vacumn(On the Hvac line) at the manifold and 7 lbs at the reservoir so I used my vacumn gage and worked my way from the manifold towards the reservoir.
What I found was that the hard line was almost broke in half after a section of hose near the battery.
Hope this helps some of you as this really bugged me for awhile.
It took 15 min. and 0 cash to fix.