Hello all, newbe here but to Cherokees. Had My '99 since 2000 and its been terrific. I've had this problem for the last few years and need to correct it. I usually use heat or AC cool thru the high center vents and as long as I'm not going slightly up hill all is well. Problem is going up even a slight grade, I need to give it a bit more throttle which decreases engine vacuum, thereby closing off the heater control flap and eliminating heat or cool air from blowing out the vents. I have a long several mile up hill commute home and over this cold winter virtually no heat for the first 8 or more miles.

I think there must be a leak in the vacuum lines some where but I can't find it. I've checked from the intake manifold, across the firewall, right fender and where it goes down to the bumper area. All looks to be in very good condition without cracks breaks and all the rubber fittings along the line look good, not hard or cracked. I haven't taken the bumper covers off to check it out there and don't know if it's necessary. I haven't checked in the cabin either.

Any ideas out there why I don't have enough vacuum or where the leak could be? If I lift the gas pedal for a couple of seconds while going up hill allowing vacuum to build, I get heat.

TIA

 

Im glad you asked that question bcs my cherokee does the same thing, and when it stops flowing from the vents, the air starts coming out from the dash. Ive tried and tried to correct this problem, but cant seem to do so just yet. My Jeep tends to do this more when im driving against windy conditions,and mine is also the same way, ill lift my foot off the pedal for a few, and then the flow starts blowing from the vents again. very strange.... So yea guys, any help in this area is greatly appreciated. thanks in advance

 

my '97 cherokee would only blow air out of the defroster vents. I pulled the vacuum line off under the hood, and had suction, so figured the problem was in the controls somehow. before taking the dash apart, I decided to check for leaks on the vacuum ball located in the front bumper. As I felt around, i thought i noticed a slight whistling. I then examined the vacuum line near the ball and was astounded to see the whole backside of the line was full of holes. My guess is that battery acid must have sprayed on the line. I replaced the line, and now everything works fine! Because I had vacuum even with a bad line, my bet is that you probably have holes too, but not near as bad as what I had. Thus, more vacuum than me, but still not enough under certain conditions.

 

this is such a common issue with jeeps... using carb cleaner, you can spray aruond vac line connections to see if you get a change in throttle. if you do, you have found a leak. there is an option to do a vac line delete that gets rid of the "unnesisary" lines...

 

Check the vacuum line/Football behind the passenger side bumper...Tj

 

To access the "football" I believe I'll have to take off the right side bumper cover and overrider assy. I'm sure I could figure this out but any help on the most direct and easiest way would be appreciated. It's well belowing freezing and I'll be doing it outside. Mine it the Classic model.

Thanks

 

If you just want to examine the ball and (vacuum line) w/o removing it, grab the plastic inner fender and pull it back..... don't do this from directly underneath or you'll probably get a face full of dirt!

If it's real cold out, it could crack the plastic when you bend it back, so be careful..