Your A/C clutch could be slipping. As for the OP's question, I'd do the water on belt trick, but also the ol' dowel rod to ear trick. Take a stick (cut off broom handle, dowel rod, what-have-you) and hold one end against your ear and put the other end in different places to determine where the noise is coming from. That's how I diagnosed a squeaky idle pulley and squeaky distributor.

 

Hi, I'm new to this, but I was reading thru the posts to see if anyone else was experiencing the same thing I am, I have a 99 Cherokee Limited, it started to make this horrible sound, kinda like a small dog was caught in the fan, at first we also thought a belt (all new) then a pulley (also new) so my mechanic really spent some time with it and came up with what's called a blend door?....it'll only make the sound when the defroster/ac is on. does yours make a thud sound when you start it and the defrost is already on? mine does, I stopped using the defrost/ac and the noise has stopped all together, but it's going in tomorrow to be fixed right.

 

I have the same problem with my jeep. It only screams at me when I am running my AC or Defrosters. I put a new belt on and checked the tension and that did not solve the problem. My roommate said that the AC compressor is turned on whenever the AC or defrosters come on but not when the regular floor heat is turned on and that the compressor clutch could be slipping or a bearing could be bad. I was checking to see if the compressor clutch could be ether rebuilt or replaced without replacing the entire compressor.

 

hey guys sorry for not responding for a while but i tigtened my serpentine and the sqeak went away. not it will only move about a quarter to half inch each way instead of a full inch how i was running it, but thatnks for off the help.

 

Jeepgirl, let us know if the AC compressor was the culprit...okay!
-prorocke

 

You bet! I haven't made in yet to have it fixed, but as soon as I do I'll let you guys know what it turned out to be and hopefully it'll help you guys too.

 

Interesting - this seems to be the problem I'm having (sorry for the slight thread hijack). The chirp came back after replacing my belt about a month ago. A bit of water quiets the belt chirp, but belt dressing makes the noise quite a bit worse. I might try the tire shine trick, as I'm just looking for a way to quiet the noise a bit. Any advice on application of the tire shine (should it be on both sides of belt, etc)? Any other thoughts on this?

 

My advice is don't do it. Belt dressing and other gimmicks are bandaids that only mask the problem. It's a pretty simple thing and there are only about 3 places the squealing noise can be coming from (assuming it is in fact related to the belt/pulleys). If you've got a new belt, scratch that off the list. Make sure it's tight enough and if the noise persists, scratch that off the list and move on to the 3rd place, which is pulleys. Even if that is the cause, it's not hard to track down which one is making the noise. (see above where I describe how to use a dowel rod for a stethoscope). If the belt is in decent shape and tight enough, my guess would be idler pulley.

 

This is what's making me try and just mask the symptom - it is a new belt (about a month old), the idler pulley was replaced at the same time and replacing the belt solved the chirp for about a month. The tension seems to be about right, but I played with the tension (more and less) on the former belt, which had less than 15K mi on it , no signs of wear, etc, and could not get the chirp to go away. I also checked the bearings on the water pump, power steering, etc by hand-turning them with the belt off - nothing seemed to be making any sort of grinding nor did I feel any out of character resistance. All signs point to a belt-friction issue. Perhaps something is out of alignment?

Others have suggested trying a goodyear over dayco belt, but since this problem has arisen only over the last few months, I am not convinced the brand is the issue. However, I did apply belt dressing to the belt, so i'll probably have to spring for a new one anyhow, since I now understand that stuff may exacerbate my issues.

 

Im having a similar problem. When I start my XJ in the morning (cold start), it chirps for a few minutes. (chirp, chirp, chirp, chirp (5-8 second pause) then it starts again. Then after it gets warmed up a little bit, it starts to squeak. And increases as RPM's increase. BUT, when the weather is warm it does not squeak at all? So it only squeaks when it's cold outside. The belt is fairly new and the idler pulley was replaced so I know that isn't the problem. Not sure whats going on?

 

I work in the auto field and have recently had this problem on my XJ. There are 2 reasons a belt makes noise assuming the pulleys and bearings in the pulleys are ok, so check them also if the tension is ok which im sure its not. The tension on the belt system on a typical 4.0ho is the PS pump and that sucks on a older motor that has rusty bolts. Your belt needs to have proper aligntemnt and tension and the latter of the 2 is why most XJ owners have belt squeel problems. I see it all the time in my business where people blame the belt but its really the stuff the belt rides on that is the problem. 9 times out of 10 a belt problem is from not being tight enough its as simple as that.

 

like i said i went through everything you guys have said. idler pulley, tensioner, altenator and it was none of those. the problem was the belt being too loose. just tighten it so when you push on it. it doesnt flex more then a quarter inch either way. if it moves more then that, its most likely causing your squeaking

 

Hey, I finally made it in and had my Jeep fixed, the "blendor" had a broken tab, if your lucky it can be glued back into place otherwise it all has to be replaced. no more squeeling and the defrost and a/c work like new.

 

I've got a nasty squeel on the 99 XJ I just bought yesterday.

The belt was squeeling just a little yesterday upon off idle throttle, but I drove it cold last night and the belt was screaming/screetching and making a oscillating scruffing noise intermittently.

I am thinking it sounds more like a idler pulley as I had that problem with my mother in law's grand cherokee 4.0.

The belt tension seems tight enough and I found a discount jeep parts website that states the idler/tensioner pullley is usually the culprite.

I know it's not the ac as it don't sound like it's coming from that area nor is the a/c clutch even engaging due to no a/c charge.

I will take the belt off today and check all the pulleys for play or restriction, and most likely get a new idler/tensioner pulley if it seems questionable as this really sounds like a bearing issue that is also affecting the belt plus the belt has a million little cracks on the ribbed side so a new belt is in order also.

I've seen bad tensioner pulley bearings lock up on other vehicles with no warning and throw or shred the belt-not good so I will see what happens and report back findings, but by the looks of this I'm sure this a very common problem with the 4.0's.

 

You may wanna start your own thread.