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A/C Pulley

2739 Views 10 Replies 4 Participants Last post by  TeflonVixen
I have a 99 E320 4Matic with 182k miles

Little background info, I had an A/C evac/recharge in April. About a month ago my blower motor or regulator went. Haven't figured out which one yet. Last week the idler pulley decided it wanted to snap in half as I was driving to dinner. In the process of it snapping it also shredded the serpentine belt. That was really fun. I fixed that this past Sunday however I am still hearing a rattling sound and another sound I can only describe as sucking air kind of.

I popped the hood and took a listen while it was running. I'm pretty sure the sound is coming from the A/C pulley. Since I have never taken a look at it prior to this, I am not sure whether or not the whole front should be spinning or not as it spins intermittently. Is it supposed to do this? Also, it appears pretty old and I'm sure the previous owner didn't replace it so I'm considering doing so. I guess I just wanted other opinions as I'm only a mechanic through this forum and youtube.


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Hello, What you see that is spinning and then not is the A/C clutch and it does cycle on and off depending on how much the compressor needs to pump the freon depending on demand of cool air. If you are hearing a bearing noise you may need a new clutch, or compressor/clutch assembly. Hopefully someone with more knowledge on this will reply soon.
Thanks for the reply!

Honestly, I'm not sure what a bearing noise would sound like. Since my fan motor has been broken I haven't really ran the A/C. I suppose I should turn it on high and observe the clutch and see what the spinning does then.

I have an appointment to get it looked at I just wanted to be a little more knowledgeable when I took it in. I found this one Amazon. I clearly love the price but does anyone have any experience with this brand?

I would be kindof leery on the amazon item:

1) the ad does not clearly state if it's new or rebuilt - at $200 for a rebuilt is about right

2) note the photo seesm to be a stock/high-quality photo and has been taken so not to show a brand/manuf tag

3) no warranty whatsoever

Personally, a new Sanden Behr/China at $250 is a much better buy - and NOT the Denso knockoff made in India which is about $180. You can call and check with these guys:

Dodge Sprinter AC Compressor, Chrysler Crossfire, Mercedes Benz New AC Compressor

Thanks for the input. I have never bought a large part (only idler pulley, window regulators, dcm etc) like this so I wasn't sure of the brand. Amazon Prime usually denotes if it is used or not in the information, as the above mentioned parts I bought have all came from here. I'll look up the brands you mentioned though! Much appreciated!
I have a slightly different opinion. The MB A/C system is always engaged unless turned off by the EC switch or by failure of the system. This is different than many domestic systems which do cycle the compressor on/off.
Your serpentine belt failure may have damaged the electric connection for the clutch on the front of the compressor. I'd check this first.
The clutch can be purchased separately.
If you decide to replace the compressor, I agree with the previous post on brand.

Sent from phone.
Thanks for the reply! I believe the compressor began to go prior to the serpentine belt failure. I was able to narrow the sound down to one of those pulleys however I just assumed it was the idler since it cracked in half. After replacing it I still hear that sound and noticed the intermittent spinning on the A/C. Thanks for the information!
Not knowing your mileage - this is a crap shoot.

Let me add some info:

1) If you have doubts whether your blower motor or your regulator has failed - 90%+ chance it is regulator. MB later updated new blower motor and new regulator for the new motor - new regulator does not work on old blower. Go to eBay since China made regulator for W140 will fit - eBay sellers sell the kit to replace the regulator.

2) Since your blower isn't working you can't tell if your compressor is working or not - so put that to the side for the moment.

3) If your original idler pulley (small plastic pulley upper passenger side) snapped - then it's a very good bet your belt tensioner is also failing. Original belt tensioner was later found to be faulty design. EZ DIY and Litens is original brand tensioner ( and DON"T use the China no name part, it's junk.
For "driveability" you need to replace that tensjoner, see the sitckies for the DIY, real easy job.

4) With new idler pulley, new belt tensioner, new belt - you are good to go

5) When you get your blower fixed, then you can start to diagnose your air con system - DON'T go replacing compressors and such until they are identified to be the problem..
Oh man, I thought I'd said 182k miles. My bad!

1) I ordered a new regulator already, it should be here Saturday. I planned on installing it the same day so that when I took it in Tuesday it would be able to see if the compressor works or not. Also, I have the new blower system so that made it easier.

2) See above :)

3) I have the new tensioner and it does not have any play, so I assumed it was okay. I'll have the mechanic look at it just to make sure. But I have driven the car about 50 mi so far and the only issue I'm seeing/hearing seems to come from the A/C clutch

4) Above :)

5) Once I fix the fan etc I'm sure it'll be easier to figure out the A/C issue. But the sound coming from that pulley is my main concern. As someone stated above it may be a bearing sound. I'm not exactly sure what that is so I can't correctly diagnose it. I just want some ideas of what I may be dealing with.

The reply is much appreciated!
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My experience with the tensioner is documented. The bottom line was that the old tensioner was 1/2 of the new in terms of the effort required to rotate it to accept the belt.
All looked OK, but I was having belt slippage and the evidence was burned rubber smell.
If I recall coreectly, the old tensioner required 25Ft lbs to rotate it and the new was double that. A non-scientific report, but you get the gist. No problems since.
My apologies for the confusion. Do you mean new tensioner in general or the new style tensioner?

I'm not sure if it's this brand but this is what it looks like
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