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AC compressor

10K views 28 replies 6 participants last post by  PerfectStorm01 
#1 ·
Over the past few days I have been trying to diagnose this low rumbling noise. I've been recording it on startup every morning and it's quite annoying-even my wife wondered what it was last night (if she can hear it that means it's very obvious). I believe it is my AC compressor on it's way out (I've heard about the "death rattle"). The noise occurs all the time lately, but only disappears after driving the car for a while but can be heard again without warning usually after startup. The noise occurs while the AC is off.

I've replaced all tensioners and belts, the w/p, thermostat and idler pulley in the last 2 weeks. P/S was replaced about a 1.5 months ago.

The sound is a low intermittent rumbling. You can hear it in this video. Compressor bearings?

My last diagnosis is removing the AC belt with the hope of isolating it. Can I remove the AC belt for a day or 2 while I drive the car around? Will this do harm? I don't think it would, but better to ask people more knowledgeable than I am.

http://youtu.be/1vqAjInK3BU
 
#4 ·
Thanks. Never really thought about compressor oil. I'll have to see if they sell something like that here.

The other source of an unexplained rattle I have come across is the heat shield for the front muffler/catalytic converter. Check that area under the car for a loose shield or hanger. There is a horizontal hanger that stabilizes the front muffler on my car that rusted through and caused at rattle at certain speeds. It was a cheap fix because everything was bolted on so it didn't involve any welding. It was item number 7 in the picture on my car..
Thanks. But wouldn't that noise be heard consistently? I can hear this noise on cold startup and after the car has been off for a while (couple hours). If I take the car for a drive it will go away. In a previous post I heard the same thing it was just lower (couldn't hear it if you didn't know what it sounded like)-now just much louder. It pisses me off when the wife hears it-she doubts my "mechanic skills" as it is.
 
#3 · (Edited)
Over the past few days I have been trying to diagnose this low rumbling noise. I've been recording it on startup every morning and it's quite annoying-even my wife wondered what it was last night (if she can hear it that means it's very obvious). I believe it is my AC compressor on it's way out (I've heard about the "death rattle"). The noise occurs all the time lately, but only disappears after driving the car for a while but can be heard again without warning usually after startup. The noise occurs while the AC is off.

I've replaced all tensioners and belts, the w/p, thermostat and idler pulley in the last 2 weeks. P/S was replaced about a 1.5 months ago.

The sound is a low intermittent rumbling. You can hear it in this video. Compressor bearings?

My last diagnosis is removing the AC belt with the hope of isolating it. Can I remove the AC belt for a day or 2 while I drive the car around? Will this do harm? I don't think it would, but better to ask people more knowledgeable than I am.
If your compressor clutch is not engaged, you should not be hearing the rattle if it is the compressor. In your previous video, the clutch was not spinning so the compressor was not supposed to be running. With the AC turned off, the clutch disengages and the compressor should not be turning at all. I don't see a problem removing the AC belt if you want to be 100% sure. It's not driving anything else. I suppose the rattle could be coming from the clutch but I've never seen that.

The other source of an unexplained rattle I have come across is the heat shield for the front muffler/catalytic converter. Check that area under the car for a loose shield or hanger. There is a horizontal hanger that stabilizes the front muffler on my car that rusted through and caused at rattle at certain speeds. It was a cheap fix because everything was bolted on so it didn't involve any welding. It was item number 7 in the picture on my car..
 

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#5 ·
I agree with this evaluation. The heat shields become "buzzy" because the fastener holes become enlarged from repeated vibration, impacts with debris on the road, etc.
I have repaired a couple of them by adding additional attachment points made from short lengths of steel strapping (from the hardware store), drilling small holes in the strapping and heat shield, and using POP rivets to hold everything together.
 
#7 ·
Could be the bearings on just the compressor pulley and not the compressor itself. On other cars this is replaceable, not sure on BMW. There is normally a circlip holding the compressor clutch assy. on, and then you can access the pulley. It will not hurt anything to take the A/C belt off to see, and if it is indeed the compressor pulley, don't wait to replace it. if you drive around like that and the bearing fails completely, bad things can happen.
 
#8 ·
This is what I am leaning towards, because I hear the sound when the AC is off and it sounds like BBs in a bowl. According to this thread you can take off the pulley and replace the bearings.

My goal is to make sure it is safe and to also quiet it down some. We are heading into fall here so the AC is not needed (does the front defroster use the compressor?), this way I can save for a new compressor-these bastards are expensive. If none of these work, I'm just going to remove the belt for the winter and look for one at a junk yard to replace it with.

I have a few things to try first though, oil and the exhaust heat shield

http://forums.bimmerforums.com/forum/showthread.php?t=860105
 
#9 ·
I had a rumble noise once on a Volvo that came on when the AC kicked on. The Volvo dealer mechanic and service advisor could not figure it out. Finally I bought a mechanics stethoscope for $12 at the auto parts store and used it to search for the noise. I discovered after awhile that it was the AC compressor mounting bolts that were loose. Moral, the stethoscope worked and I have used it numerous times since to help diagnose unusual noises.
 
#15 ·
So I bought myself a stethoscope. I put the rod on the AC compressor and it doesn't sound odd, just a spinning sound. No rattling or odd noise. If there were some bearing issues/rattles it would be obvious right? I checked my waterpump and it sounded smooth; I checked my powersteering resevoir just in case and it was smooth.

I just drove the car so now the sound is gone. I want to wait until it cools down so I can get under the car and look at the exhaust as mentioned above for any loose heat shields, etc.

I feel a bit better that the AC and waterpump seem to be smooth, but I want to get under the car to see if I can shake the compressor to see if it is loose, maybe take the belt off just for kicks to see if I still hear it.

What about my fan (I have an auto). If for any reason the clutch was off balance would it make that noise (BTW it can be heard under the hood and in the cabin). How can I tell? The fan doesn't wobble.

Engine mounts? Would they vibrate all the time(or just over bumps) or would it be more pronounced at cold start up when the engine idles higher?

I still have a bit to do, but I want to keep everyone in the loop and perhaps something may come to mind that you can share. Seriously, what would rattle or make the noise in the video only at cold start up and then disappear after driving for a bit? It has to be something that requires lubrication/oil, right? :mad::dunno:

This is the frustrating part because I don't know enough about this car to help, I feel like I'm just "chucking ideas" out there.
 
#17 ·
Is it possible to have a bearing/rattle/noise coming from the alternator and it still charge correctly? After more research, I have taken a harder look at the alternator. I will need to wait until the morning, but things don't sound clean coming from the alt.

I unlocked the battery charge on the obc and it sits around 14-14.2 while idling and went from around 12 to 8.9 when starting.
 
#18 ·
Yes it is possible but if the alternator is rattling, you won't have much time before it suddenly dies. The rattling most likely won't be coming from bearings but rather bearing failure allowing the rotor to rattle around hitting the stator. You will need a new alternator very soon if that's the problem.
 
#27 · (Edited)
My apologies for not providing an update to this thread, but I had a few things to take care of. I personally hate when OPs don't provide closure, so here is my update.

My alternator wasn't the "complete" issue. I replaced it and it made all sorts of internal rattling noises, it even had leaves in it. Don't ask. My noise still persisted.

At this point, everything was new from the pulleys to the PS pump. I couldn't figure it out so I caved and sent the car off to the dealer since I was nervous something more critical was wrong with the car. Apparently, it gave the tech a few headaches too, but ultimatley it turned out to be the new drive belt I put on it. There has been tons of talk on this forum about OEM v. aftermarket parts and I guess belts can fall in the category as well. The tech put a a bmw belt on it and the noise is gone. The tech couldn't say for sure why, but he did say that the belt I had on it could have been fractionally larger and it was just sort of "flopping" around, in other words, it wasn't fitting snuggly or maybe it was made from a different material and when it was cold it just didn't function correctly. I don't think I would have found it because the belt was the farthest thing from my mind based on the noise. The tech said it wasn't typical belt noise either. So far, it worked when he replaced it and they kept the car one more day and tested it again this morning in the rain and it was perfect. I showed up a few hours later to pick it up and it was like butta. When I start it in the morning I'll update again. What a saga...

If your curious the belt I originally put on it was an 6PK1540 Optibelt-RB 2G.
 
#28 · (Edited)
My apologies for not providing an update to this thread, but I had a few things to take care of. I personally hate when OPs don't provide closure, so here is my update.

My alternator wasn't the "complete" issue. I replaced it and it made all sorts of internal rattling noises, it even had leaves in it. Don't ask. My noise still persisted.

At this point, everything was new from the pulleys to the PS pump. I couldn't figure it out so I caved and sent the car off to the dealer since I was nervous something more critical was wrong with the car. Apparently, it gave the tech a few headaches too, but ultimatley it turned out to be the new drive belt I put on it. There has been tons of talk on this forum about OEM v. aftermarket parts and I guess belts can fall in the category as well. The tech put a a bmw belt on it and the noise is gone. The tech couldn't say for sure why, but he did say that the belt I had on it could have been fractionally larger and it was just sort of "flopping" around, in other words, it wasn't fitting snuggly or maybe it was made from a different material and when it was cold it just didn't function correctly. I don't think I would have found it because the belt was the farthest thing from my mind based on the noise. The tech said it wasn't typical belt noise either. So far, it worked when he replaced it and they kept the car one more day and tested it again this morning in the rain and it was perfect. I showed up a few hours later to pick it up and it was like butta. When I start it in the morning I'll update again. What a saga...

If your curious the belt I originally put on it was an 6PK1540 Optibelt-RB 2G.
Thanks for the update but I had assumed your story had a happy ending until next time.

The dealer mechanics have one luxury most of us don't, including the Indys. They have access to the complete inventory of parts for the car at the dealership and can try different options. If it doesn't work, the part can quietly go back on the shelf. For the rest of us, we try, we buy. Especially electrical parts.
 
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