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Strange chirping sound from engine bay when defroster selected

sniperdude

NAXJA Forum User
Location
Illinois
I found a weird problem with my 97 Cherokee. Whenever I put the fan vent selector on the defog/defrost settings, either one of them, I get a real loud annoying chirping sound from the engine bay.

Sounds more like it comes from the driver's side. The sound increases in speed and volume when the gas is pressed.

If I turn the fan vent selector to any of the selectors without the defrost/defog option, the sound goes away almost immediately. But if I put it back on defroster, it will immediately kick back in.

Have no idea what this is, but it will be extremely annoying during winter. I'd like to see if any of you know what this is. I've done some searching, but can't seem to find anyone with my identical issue.

Thanks!
 
The A/C compressor is engaged in the defrost mode.... You either have a noisey compressor or a worn/loose serpentine belt..... I would tend to think the belt is the most likely culprit..... the tension on these belts is needs to be tighter than most would guess.... It is difficult to set without a tension tool....
 
Agreed with all the above -
The compressor runs on the belt. and the compressor turns on when you turn to defrost - because the air conditioning system puts out DRY air (versus moist/damp air), which will clean the moisture off your windows faster.

the belt is chirping because of the torque required to spin the compressor

:)
 
Just out of curiosity, what's the avg life span on a serpentine belt? I only ask b/c I've had mine a little over 2 years.
 
Serpentine belts can last a long time.

I've been going on my original in the TJ for more than 9 years now. I do have a backup in the rig if it ever breaks but it is still going strong.

Funny thing is, I had a mechanic buddy tell me it was going to go about 5 years ago.

The basic rule of thumb is, when it starts to develop cracks, it is time to replace it.
 
Serpentine belts can last a long time.

I've been going on my original in the TJ for more than 9 years now. I do have a backup in the rig if it ever breaks but it is still going strong.

Funny thing is, I had a mechanic buddy tell me it was going to go about 5 years ago.

The basic rule of thumb is, when it starts to develop cracks, it is time to replace it.

Cool thanks!
 
Have you messed with the belt at all lately? If so, make sure it's plenty tight. You'll have to tighten it down more than you thought you'd need to to keep it from squealing, and make sure everything works properly.
 
My XJ needs a very tight belt in order to keep the squealing/chirping at bay. It needs to be tighter than any other vehicle I have ever owned. Start there....
 
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