Rattling/knocking sound when the compressor is engaged. Not to loud. Much louder for first couple of seconds after engaging. No change in engine RPM. It's quiet with the compressor turned off. Everything is working fine. I would like to be certain the compressor is really bad before tearing into it. If I remove the serpentine belt and turn the compressor by hand (with the clutch engaged) will that cinch it? Is there any possibility something else would only be noisy while the compressor is running?

From what I've read in old threads, I'm looking at a new compressor. Just hoping it could be something else.
Thanks, Dan

1999 C280

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2012 E350 Bluetech

It could be the belt tensioner - you can watch it, when it is making the noise it will vibrate badly.
You don't have the remove the belt from the compressor to turn it. Just grab the front of the clutch and give it a turn, this turns the inside of the compressor. This probably wont tell you anything unless it is a bearing then it might feel kind of rough. I have found that making a diagnosis from the way the compressor turns is a bad idea.
You could carefully put a long screwdriver (2' or3') on it while it is running to verify where the noise is coming from, or buy a stethescope at the local parts store to help locate the noise. But definitly check the tensioner.

Thanks for the reply. I'll look at the tensioner and post what I find.
Dan

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2012 E350 Bluetech

Dan:

Sounds just like the noise I was having with my 1999 C230 K. It was in fact the supercharger. I replaced it myself for $655 all parts included and three hours labor. I had it verified in advance that it was for sure the compressor. All you have to do is remove the supercharger belt and run the engine without it and if you don't hear the sound, then there you go. The belt does turn anything else. When I got my S/C out, it was clear that the bearings inside the unit were on their way out. Good luck.

JB

Thanks JB
The problem is in the C280, no supercharger. Good info, though. There is also a C230 in the barn so maybe someday...
Dan

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2012 E350 Bluetech

My oops. WHen I saw compressor, I thought you meant the S/C. I didn't see any reference to the A/C unit. Although, that being said, the clutch unit on both the A/C and the S/C are very similar but I don't think that is what gives way on these things. Anyway, good luck with solving your problem.

JB

The compressor in my 78 bmw has been doing exactly that...I added a bit more oil into the system...noise a biy quieter but still there.
I will just keep using it until the air gets warm or the compressor explodes.

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82 300D....went to MB heaven
90 350 SDL....excercising con rods

I just commented to someone else about this...

Assuming that the noise came on gradually and not all at once (when I say gradually I mean over a matter of several weeks) then it is possible that it just needs oil.

Andmoon - the noise that a compressor that is low on oil makes is the noise of the compressor slowly destroying itself, to put it simply. When you put more oil in the noise doesn't necessarily completely go away but it will alleviate most of the noise/wear problems. The life of the compressor may have been reduced from running it like that, but it will still work for at least a while.

If I decide to try adding some oil, how would I do it? Would it have to go to a shop with special equipment?

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2012 E350 Bluetech

If you have 134a, then they sell it in a can...low side and run a/c.
For R12 I have no clue.

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82 300D....went to MB heaven
90 350 SDL....excercising con rods

I was asking about adding oil, not refrigerant.
Thanks

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2012 E350 Bluetech

I found some old posts that described a similar sound which was caused by a bad clutch.
Any comments from all you know-it-alls
Dan

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2012 E350 Bluetech

The dealer uses a syringe type device to insert some oil into a screw in port in the compressor. Car parts shops sell ester oil in either a 2 ounce can or an 8 ounce can mixed with some refrigerant for pressure to force it into the system. The syringe method would be the preferred method because you can just inject it until it doesn't make noise anymore, but whether you could get your hands on one of those devices cheap I don't really know. I'm also not sure that ester oil is the correct oil. I talked to a mechanic at a dealership and he told me thats what they use but I'm still skeptical that the correct oil.

I removed the belt to get better access. The tensioner and clutch pulleys turned smoothly without any play, however when I tried grabbing the front of the clutch to turn the shaft, I was just barely able to rotate it. It feels like something is seriously binding up inside the compressor. I think I'm lucky it didn't freeze-up on me.
It looks like ACKITS or ACSOURCE are good sources for rebuilt units.

Also, after I've removed the compressor, what should I look for to determine if I need to flush or not?

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2012 E350 Bluetech

Make the flush SOP and you won't go wrong.

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Jim