AC compressor

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.

Id be inclined to put some oil into the A/C system. In the states we can buy it in a can much like R-134a. Hook it to the low side port and open the can.

Originally Posted by PerfectStorm01

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..

Originally Posted by smolck

Id be inclined to put some oil into the A/C system. In the states we can buy it in a can much like R-134a. Hook it to the low side port and open the can.

Thanks. Never really thought about compressor oil. I'll have to see if they sell something like that here.

Originally Posted by ckleung100

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.

Originally Posted by ckleung100

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..

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.

Originally Posted by PerfectStorm01

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.

Intermittent noises are the hardest to diagnose. I suggested checking the exhaust as part of your process of elimination since you have already replaced all tensioners and belts, the w/p, thermostat and idler pulley in the last 2 weeks. You just need to crawl under the car to check.

If it were the compressor, that noise would be constant too whenever the AC compressor is engaged. To be sure, you turn the AC to the lowest setting to force it to engage. Once you see the clutch spinning, you know the compressor is turning and the noise should start.

Originally Posted by PerfectStorm01

It pisses me off when the wife hears it-she doubts my "mechanic skills" as it is.

Join the Club....

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.

Originally Posted by SJBimmer

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.

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...d.php?t=860105

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.

My experience is that faulty bearings squeal, not rattle.

Originally Posted by ckleung100

My experience is that faulty bearings squeal, not rattle.

That's because you are catching them when they first start to fail. When they get really bad, they rattle.

Originally Posted by PerfectStorm01

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...d.php?t=860105

Front defroster uses the A/C and buying anything that has bearings in it from a junkyard, unless it lives in an oil bath, is a bad idea. You have no idea how long the part has been sitting, and if there is any rust on the bearing, it will fail rather rapidly. I have replaced numerous compressor clutches and pulleys, and trust me on this, it not a job you want to do twice. The actual replacement is not difficult, it is getting access to the compressor, and the clearance necessary to remove the parts. The pulley and bearing might run you $150 max. Is it worth it? Plus if you let the compressor sit too long without being used, the seals will dry out and leak, and you will then need to evacuate the system and replace the compressor. When you pay the bill for all of that, it will really make your day.

Originally Posted by SJBimmer

That's because you are catching them when they first start to fail. When they get really bad, they rattle.

You are right on that point. When it start squealing like a pig, I don't wait long enough for it to develop into a rattle.

Originally Posted by ckleung100

You are right on that point. When it start squealing like a pig, I don't wait long enough for it to develop into a rattle.

Me neither! I'm OCD when it comes to my cars. My Wife thinks I'm nuts.

Originally Posted by djs1122

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.

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?

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.

Originally Posted by SJBimmer

Front defroster uses the A/C and buying anything that has bearings in it from a junkyard, unless it lives in an oil bath, is a bad idea. You have no idea how long the part has been sitting, and if there is any rust on the bearing, it will fail rather rapidly. I have replaced numerous compressor clutches and pulleys, and trust me on this, it not a job you want to do twice. The actual replacement is not difficult, it is getting access to the compressor, and the clearance necessary to remove the parts. The pulley and bearing might run you $150 max. Is it worth it? Plus if you let the compressor sit too long without being used, the seals will dry out and leak, and you will then need to evacuate the system and replace the compressor. When you pay the bill for all of that, it will really make your day.

You're right. I looked on oembimmerparts.com and found the compressor kit for $460. I can get this shipped to oz, pay tax on it and it will still be 2/3 of the price of a new stand alone compressor here. Based on above, it may not even be the compressor now...

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.

Originally Posted by PerfectStorm01

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.

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.

Originally Posted by ckleung100

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.

Update - I removed my fan and started the car...sound still there; I removed the AC belt...sound still there. I feel like a doctor cause I'm listening to everything that has a belt on it using the stethescope.
My next question is can I remove the main belt and start the car (for like a minute) just so that I can hear if the sound is still there? I'm going to give the car about 30 minutes before I do this. I wanna make sure it isn't too warm before taking the belt off. By doing this I am sure that I will have a few lights (battery) light up on my dash. Anything else to look out for?

Originally Posted by PerfectStorm01

Update - I removed my fan and started the car...sound still there; I removed the AC belt...sound still there. I feel like a doctor cause I'm listening to everything that has a belt on it using the stethescope.
My next question is can I remove the main belt and start the car (for like a minute) just so that I can hear if the sound is still there? I'm going to give the car about 30 minutes before I do this. I wanna make sure it isn't too warm before taking the belt off. By doing this I am sure that I will have a few lights (battery) light up on my dash. Anything else to look out for?

You can remove the main belt and run the car, but for no more than a few minutes. Do it when the car is dead cold.

Originally Posted by SJBimmer

You can remove the main belt and run the car, but for no more than a few minutes. Do it when the car is dead cold.

Thanks. I did it last night and this morning and the noise was gone. The way I see it is I can leave it alone and live with the noise, but it drives me or replace my alternator, which is the only original accessory on my main belt since everything else has been replaced within the last 2 months. Both my alternator and battery are original, so I am guessing a bit of preventive maintenace wouldn't hurt either way. What do you think?

If the alternator is rattling, the decision may be made for you pretty soon....

Originally Posted by PerfectStorm01

Thanks. I did it last night and this morning and the noise was gone. The way I see it is I can leave it alone and live with the noise, but it drives me or replace my alternator, which is the only original accessory on my main belt since everything else has been replaced within the last 2 months. Both my alternator and battery are original, so I am guessing a bit of preventive maintenace wouldn't hurt either way. What do you think?

There is one last remote possibility. I read somewhere on another thread that if you replaced you defective mechanical tensioner with a replacement mechanical tensioner, the oil filter housing that the tensioner connects to may be touching the tensioner, causing the rattle. This is why BMW was changing mechanical tensioners to the hydraulic tensioner when the customer had this rattle complaint. My mechanical tensioner was rattling only when I first started the car, and did not do it when warm when I bought my car as a CPO, and BMW swapped in the hydraulic tensioner assembly at no charge. The hydraulic tensioner uses different mounting holes than the mechanical tensioner, and has 3 mounting points compared to two for the mechanical. If I recall correctly, the mounting holes become distorted, or distort the oil filter housing enough to allow contact with the back of the tensioner, which can also cause oil filter housing gasket leakage if I recall correctly. I tried searching for the thread, but could not find it. Just a last thought, and I hope you find a solution to your problem. If removing the belt eliminated the noise, it has to be one of the parts that rotate. Keep checking them one by one and you will find it. Good luck!

if you have a stethoscope, you should be able to isolate the sound to the tensioners, water pump or the alternator.

Originally Posted by SJBimmer

There is one last remote possibility. I read somewhere on another thread that if you replaced you defective mechanical tensioner with a replacement mechanical tensioner, the oil filter housing that the tensioner connects to may be touching the tensioner, causing the rattle. This is why BMW was changing mechanical tensioners to the hydraulic tensioner when the customer had this rattle complaint. My mechanical tensioner was rattling only when I first started the car, and did not do it when warm when I bought my car as a CPO, and BMW swapped in the hydraulic tensioner assembly at no charge. The hydraulic tensioner uses different mounting holes than the mechanical tensioner, and has 3 mounting points compared to two for the mechanical. If I recall correctly, the mounting holes become distorted, or distort the oil filter housing enough to allow contact with the back of the tensioner, which can also cause oil filter housing gasket leakage if I recall correctly. I tried searching for the thread, but could not find it. Just a last thought, and I hope you find a solution to your problem. If removing the belt eliminated the noise, it has to be one of the parts that rotate. Keep checking them one by one and you will find it. Good luck!

I just checked and my mech tensioner doesn't touch the OFH other than where it connects to it. My idler pulley seems to be connected to my alternator though. I guess I never really realised it.

Originally Posted by ckleung100

if you have a stethoscope, you should be able to isolate the sound to the tensioners, water pump or the alternator.

Just call me doctor - I bought one the other day.

**UPDATE**
I think I have found my rumbling noise...it's my alternator. I believe that I was applying too much pressure with the stethescope to hear a clear, definitive sound (in fact I was getting some engine noise interference). Thanks to Smolck, telling me to check it again, I did. By applying "light pressure" to the alternator casing, directly above the bearings, I could hear my rumbling. You almost have to work the scope because depending on the angle, pressure and outside noise you could miss it. I am going to order my alternator tonight for install tomorrow. FINGERS CROSSED!

Thank you to ckleung, sjbimmer, smolck and everyone else who has been there from the beginning with great advice and ideas. Hopefully this is the end of the insanity and we can move on to more pressing issues. Wish me luck for tomorrow and I will hopefully post my last update on this thread once and for all.