99 Xj (AUTOMATIC) When operating the A/C and or vent during acceleration they blow air fine but once I get up in 3 or 4th gear. The air stops blowing through the vents and begins making more of a whistle/hissing noise coming from the defroster vents. If I turn the fan down to low the whistling/hissing noise goes away or if I decelerate quickly it also works normally.

Could it be the fresh air intake may be open? Is the 99 equipped with this? I know both 95's had one

Any help would be appreciated. Thanks in advance.

By the way I posted an issue with the horn causing a check engine light to come on. They determined it was a short but unable to locate it. So I now have a horn wired seperatly and it works like a charm.

 

Sounds like maybe there's a vacuum leak. AFAIK the vent dampers are vacuum driven. If you look at the back of the climate controls in the cab, there's no wires going to that section. Just vacuum hoses (in every color in the rainbow).

Hope that helps

-bob-

 

ok I will check that

 

The info about the back of the climate control was basically for illustration purposes only. I wouldn't tear that apart unless you really think the problem is in the cab. I would start by checking under the hood. Look for cracks at fittings and at small hoses that may have simply fallen off somewhere. When I had this problem with my 91, it turned out to be a small hose leading to behind the front bumper (no idea where it was supposed to go). I plugged it off and voila....vent controls again.

-bob-

 

sounds like the check valve in the vacum lin to either vacuum canister or to vent control is leacking

 

Where would I find this canister? Also what does it look like?

 

Round ball located in the front bumper. There is a "T" ftting on the passenger side fender, in the area of the fuse box. That leads down to the vac. canister in the bumper. They use crappy plastic line rather than rubber, and it is very prone to cracking. Plug the "T" if you dont feel like taking the front bumper off.
Ben

 

Ok found the leak apparently the plastic junk got under battery and wore a hole how would I go about fixing it. It is chewed up pretty bad. Rest of tubing looks good. Still unsure what the hell is the canister doing in the bumper? Thanks fgor helping me find the issue!!!

 

disconnect the line that goes from the ball to the "T" fitting and plug the "T" with a bolt and zip tie. Drive it around for a day or so and see if you can live with it. Lots of guys run with out the ball and say its no different. If for some reason you must have it in then cut a small piece of the plastic line, head to local parts store, and find a piece of vacum line that will fight tightly over the outside. Cut the plastic line off flush and use vacum line to reconnect. Make sure to route it around the battery and not under.
Ben

 

I had the same problem,checked under the battery holder and there it was,
tube broken and the wire harness and wires were exposed. Taped wires and fixed tube. Cleaned up the mess tie wrapped the wires and tubes, road tested. FIXED. Seems to run better, what other problems did this fix?