Knocking at idle with AC on

[JaredSi]

Hello all,

I have a 2004 KJ w/ 3.7 and 150k. At idle when the AC is on, there is a very loud knocking sound that sounds like it's coming from the AC compressor. It also only manifests itself when the engine is warm. The sound will go away immediately with any amount of throttle. I've replaced the idler pulley, it was worn and gnarled but not the cause of the sound. I then tried to replace the entire tensioner assembly but that did not fix the issue either so I returned the assembly.

I should mention the AC compressor works great and is blowing very cold air, consistently. The clutch is not clicking on and off rapidly. I ordered a new clutch/pulley set for the AC and set about installing it today. I noticed that the old clutch is very unevenly worn on one side. The pulley seemed to be in good shape though with no play or sound from the bearing.

However when installing the new clutch the old spacer does not give enough clearance and the spacers that came with the kit do not fit. So I reinstalled the old pulley/clutch and even though I cleaned everything and lightly tapped on the pulley with a mallet, the sound returned and did not change at all in tone or frequency. It is not a sound that is consistent or one that matches the engine frequency.

What do you think could be the cause of the sound? I suppose it could be the AC Compressor itself but considering how well it works I'm doubting that. Since it does work so well I'm hesitant to have it flushed and recharged as I'm afraid if something is wrong with it, I'll have to replace the whole unit.

Thanks!

 

[jeeptorino68]

i had an issue like this. turned out to the the waterpump for me.
you can follow my thread about it here:
http://www.jeepkj.com/forum/f196/engine-noise-2002-3-7-a-59952/index6.html

 

[J33Pfan]

get one of those stethoscopes from the auto parts store to listen to where the sound is the loudest. yea, it could be your compressor

 

[tjkj2002]

I'd try a new belt and tensioner assembly.

Sounds like a tensioner but even replacing it and still using a worn belt defeats the whole purpose.

 

[J33Pfan]

ummm AC working Great in the winter time @ 64 deg outside -that doesnt count.

Well I had some cars with a bearing knock that ran great too

 

[JaredSi]

ummm AC working Great in the winter time @ 64 deg outside -that doesnt count.

Well I had some cars with a bearing knock that ran great too

Knock has been happening for over a year, through a very hot summer last year, compressor still performs well.

Good to know cold air in the winter time is not an indicator of compressor health. /s

Side note: Knock does not occur with serpentine belt removed.

 

[J33Pfan]

Knock has been happening for over a year, through a very hot summer last year, compressor still performs well.

Good to know cold air in the winter time is not an indicator of compressor health. /s

Side note: Knock does not occur with serpentine belt removed.

what im trying to say is that if the compressor has a knock, it could still run good with a knock. only problem, if it is worn or damaged internally its filling up the AC system with metal fragments. The whole system could get totaled out by metal debris

 

[jeeptorino68]

Knock has been happening for over a year, through a very hot summer last year, compressor still performs well.

Good to know cold air in the winter time is not an indicator of compressor health. /s

Side note: Knock does not occur with serpentine belt removed.

did you read through what i posted?
check everything thoroughly...mine turned out to be my last (and least likely) culprit...the waterpump

 

[JaredSi]

did you read through what i posted?
check everything thoroughly...mine turned out to be my last (and least likely) culprit...the waterpump

I read the thread about your issue and you mentioned that the knock was always audible. In my case, it is only audible when the A/C clutch is engaged and the engine is warm. I'm not ruling anything out at the moment, I'm only trying to find the most likely and cost effective parts to replace first.

I should be getting the correct spacers for the A/C clutch tomorrow and will be able to rule that out. If that does not solve the problem, I will replace the tensioner assembly with a new belt as tjkj2002 suggested. If the problem still exists after doing that I will either, bypass the AC compressor or replace the whole unit. Only after doing that will I look towards the water pump as it seems the most unlikely in my case.

 

[J33Pfan]

I read the thread about your issue and you mentioned that the knock was always audible. In my case, it is only audible when the A/C clutch is engaged and the engine is warm. I'm not ruling anything out at the moment, I'm only trying to find the most likely and cost effective parts to replace first.

I should be getting the correct spacers for the A/C clutch tomorrow and will be able to rule that out. If that does not solve the problem, I will replace the tensioner assembly with a new belt as tjkj2002 suggested. If the problem still exists after doing that I will either, bypass the AC compressor or replace the whole unit. Only after doing that will I look towards the water pump as it seems the most unlikely in my case.

if compressor is the noise problem -you dont have to bypass the compressor. just disconnect the clutch wire so the compressor doesnt turn. seems the pulley bearing is still good or not the noise problem.

 

[JaredSi]

if compressor is the noise problem -you dont have to bypass the compressor. just disconnect the clutch wire so the compressor doesnt turn. seems the pulley bearing is still good or not the noise problem.

That's a good point. I just finished putting the new clutch assembly on, did not fix issue. I'll just disconnect the clutch wire for now so I don't destroy my whole AC system, until I get a new compressor installed.

Thanks for your help