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  #16  
Old 09-11-2017, 09:41 PM
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In addition to removing the belt, check the clearance of the fan to the shroud. It can rub as the result of a collapsed mount.

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  #17  
Old 09-11-2017, 10:48 PM
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Quote:
Originally Posted by Mxfrank View Post
In addition to removing the belt, check the clearance of the fan to the shroud. It can rub as the result of a collapsed mount.
Which mount? Fan, clutch, and shroud are all new. Same noise before and after.
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  #18  
Old 09-11-2017, 11:45 PM
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Quote:
Originally Posted by Bimmer-Bob View Post
Which mount? Fan, clutch, and shroud are all new. Same noise before and after.
Engine mounts. If they collapse they can cause the engine to ride lower and the fan can strike the shroud. Still sounds like a shrieking bearing to me.
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  #19  
Old 09-12-2017, 12:36 AM
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Quote:
Originally Posted by Diseasel300 View Post
Engine mounts. If they collapse they can cause the engine to ride lower and the fan can strike the shroud. Still sounds like a shrieking bearing to me.
Yeah, me too. Anyway, engine mounts were replaced last year (cause they were flat).
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  #20  
Old 09-12-2017, 10:49 AM
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Was able to pop my head under the hood right as I got to work and it made the noise once, briefly. I can't say for sure, but it sounded like it was coming from the driver's side (i.e., not the alternator). I won't have time to pull the belt (and also maybe pick up an auto stethoscope) until Friday, but is it possible that it could be on the that side? It sounded lower, like the AC compressor, but the noise happens even if the AC is off and I usually run in "EC" mode (AC doesn't work anyway - blows but doesn't cool). I guess it could be the PS pump on that side as well. Fluid was good there, BTW.
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  #21  
Old 09-12-2017, 11:23 AM
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It could easily be the A/C compressor pulley. It is on the driver's side and down low. Even if the compressor isn't running the pulley is still turning. There's a bearing on the shaft that could easily be toast. If it's dried out and failing, it'll make a heck of a racket.
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  #22  
Old 09-12-2017, 11:56 AM
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Originally Posted by Diseasel300 View Post
It could easily be the A/C compressor pulley. It is on the driver's side and down low. Even if the compressor isn't running the pulley is still turning. There's a bearing on the shaft that could easily be toast. If it's dried out and failing, it'll make a heck of a racket.
I'll pick up some ears and start there. I really don't want to have to replace a compressor with non-functioning AC, though. Do you know if the is pulley serviceable? Can I just bypass the thing with a shorter belt?
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  #23  
Old 09-12-2017, 12:24 PM
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Yes there is a shorter belt, the EPC (electronic parts catalog) can help you suss out the part number:

Mercedes-Benz Teilekatalog (Ersatzteile online)

I'm not sure about the bearing in the pulley / clutch assembly being responsible, if the noise is present even when the clutch is engaged. However, if your refrigerant charge is low and the clutch is not engaging, then perhaps it could be that pulley. Easy to check, remove the serpentine belt and spin it by hand, and if you feel any roughness or hear any noise, that is your most likely suspect. I believe a special tool is required to pull the clutch while leaving the compressor mounted, but maybe just the pulley can be removed without that tool.
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  #24  
Old 09-15-2017, 05:22 PM
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Noise is 100% the AC compressor. Doesn't matter if the AC is on or off, the clutch is constantly engaging and disengaging, making that noise. Glad to finally have it narrowed down to one thing, but that leaves me with what to do about it.

The easiest, fastest, and most economical thing to do would just be to bypass the compressor with a shorter belt. I tried the Teilekatalog link above, but couldn't find more than one belt listed (likely the one that's already on the car). So I decided to check Continental's web site. I figured I should check the European site, since I doubt the W124 was sold without AC in the US market. Sure enough, under 250D Turbo, Conti lists 3 belts to choose from. If I'm reading this right, the belt I want should be the second option, 6PK2030 (vs the slightly longer 6PK2100 that's on the car now):

Let's play "What's That Noise?" (OM602 Edition)-screen-shot-2017-09-15-2.08.32-pm.png

The trouble, of course, will be finding this belt in the US. I haven't looked very hard yet, but so far the only thing I could find in that size (on Amazon) was by a company named "Bando" or something - I'm really much more interested in an OEM Continental belt. I guess worst case I can probably find one overseas, but it won't be here in time for a repair this weekend.

EDIT: Actually, I think Continental just has a different p/n for that belt - I assumed it was a standard size. Their US site cross-references the Bando number - so maybe Bando is the OEM?

EDIT 2: Ok, actually the 6PK2030 IS a metric size - for some reason the Conti part that cross-references that Bando belt size is actually a 6PK2025 - is that "close enough?"


The second option is to replace the entire compressor. This is obviously much more expensive and labor-intensive, and frankly stupid considering that my AC doesn't even work. But is it possible that it hasn't worked this entire time because the compressor is broken? Or should the compressor still be functional even though it's noisy? An indy mechanic who looked at the car told me he thought my problem was a leaky evaporator core or expansion valve, so that's probably it - but it still has me wondering.

Another thing is, I know this car is 25 years old, but the climate control system is ****! Assuming that mechanic was correct, that means that the evaporator core and compressor, as well as the blower motor and air sampler motor (the last two both replaced by me) have all failed...and maybe some other components I'm not aware of yet. Geez, I expect something to fail, but is seems like the whole system is dying.

Anyway, off to hunt for this belt...thanks everyone for your helpful input.
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Last edited by Bimmer-Bob; 09-15-2017 at 05:32 PM.
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  #25  
Old 09-15-2017, 06:27 PM
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If the issue is that the compressor is somehow being turned on and off, why not just disconnect it's power lead?
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  #26  
Old 09-15-2017, 07:27 PM
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Quote:
Originally Posted by Mxfrank View Post
If the issue is that the compressor is somehow being turned on and off, why not just disconnect it's power lead?
I'm not sure that the issue is that the compressor is receiving power while turned off, but that this bearing is making noise weather the unit is powered or not.
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  #27  
Old 09-16-2017, 12:31 PM
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So anyone know if I ca use a belt that's 5mm too small without too much worry? It seems like a very small difference. I have one en route that'll be here tomorrow. Alternatively, I think I found the correct size (finally, and cheaper) but it wouldn't arrive until later in the week. Thoughts?
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  #28  
Old 09-16-2017, 01:02 PM
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The part you are turning in your video is the actual compressor hub, the part that gets pulled in by the clutch. Spin the pulley itself, is it quiet? If it is, simply unplug the compressor so it doesn't run. If it is disabled, it shouldn't be pulling in and cycling. If the refrigerant has all leaked out, it shouldn't be running anyway. If the center hub is being pulled in and cycling with no refrigerant, no wonder it's so loud!
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  #29  
Old 09-16-2017, 01:08 PM
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Originally Posted by Diseasel300 View Post
The part you are turning in your video is the actual compressor hub, the part that gets pulled in by the clutch. Spin the pulley itself, is it quiet? If it is, simply unplug the compressor so it doesn't run. If it is disabled, it shouldn't be pulling in and cycling. If the refrigerant has all leaked out, it shouldn't be running anyway. If the center hub is being pulled in and cycling with no refrigerant, no wonder it's so loud!
Yeah, AFAIK the refrigerant is gone. But why would the compressor be cycling on and off when the AC is switched off?
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  #30  
Old 09-16-2017, 01:10 PM
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It shouldn't be. There's a pressure switch on the receiver/dryer that should disable the compressor. You probably have problems with the Klima relay. Mine was flat empty and the Klima relay was stuck "on". Turned the compressor into TOAST and locked up solid.

If the pulley is smooth, I'd just unplug the compressor (there's a 3 pin plug on top of it) and move on with life.

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