ac problem

I have a 98 cherokee sport with a 4.0 and auto trans and my ac works really good when im driveing in town but as soon as I get up to highway speeds the ac quits blowing out of my vents and switches to the defrost vents and it will switch back off and on between the 2 as im driveing has anyone else had this problem if so what did you do to fix it before I dig to deep into it thanks

I think I've heard this has to do with some sort of vacuum leak. Can't quite remember the conversation, though.

I'm sure if you went out to google, put in naxja a/c vents switching, you'll get some good hits.

Yes, vacuum related. The switching vents are actuated by vacuum. With no vacuum (or low vacuum) the vents go to the defrost position (default position).

Now, at higher throttle, the engine produces less vacuum. So, a vacuum leak may be masked at low throttle settings, but manifest at higher throttle settings. Follow vacuum lines to find the leak. Would start at the vacuum tank (coffee can located behind front bumper on pass. side), then check where vacuum lines pass under battery holder...two likely canditates.

Good luck!

This info helped me, i had the same problem and it was a vacuum leak just behind the battery where the hood prop is held. Thanks

madska636 said:

This info helped me, i had the same problem and it was a vacuum leak just behind the battery where the hood prop is held. Thanks

Click to expand...

Hmmm....x2.

This could be why I lose airflow after awhile and then I hear what sounds like a door closing and the air flows freely again.

Definitely a vacuum leak problem. Try having some one kill the engine, then listen under the hood for the leak to find it. I had a brand new vac hose that was not round on the inside with a slow leak give this head ache once. Only way I could find it (as it was a new part that was internally defective) was to listen for the leak with everything powered down.