ac compressor making a bad bearing noise when off?

[The motor guy]

I did some poking around with the engine idling and listened for about 5 minutes mainly admiring the sound of the cummins (sorry) Anyways, I noticed whenever the clutch isn't engaged it makes a slight metal on metal bearing noise, but when it engages and spins it doesn't make any noise at all. So does this mean I need a new compressor? Is the whole thing going to seize up eventually and cause the belt to break? Now the noise isn't too noticeable only the average paranoid nut like me would notice it, but it is obvious if you're listening. The ac compressor is on the very bottom of the truck, could it just need to be recharged? The ac still works great.

 

[DBMaster]

There is a bearing that allows the compressor pulley to spin freely when the compressor clutch is not engaged. The bearing gets locked along with the pulley when the clutch engages. I actually have had a pulley bearing fail in a car (1972 Pontiac). The repair shop was able to pull the old clutch/pulley assembly and replace it without even opening up the sealed system.

 

[The motor guy]

Originally Posted By: DBMaster
There is a bearing that allows the compressor pulley to spin freely when the compressor clutch is not engaged. The bearing gets locked along with the pulley when the clutch engages. I actually have had a pulley bearing fail in a car (1972 Pontiac). The repair shop was able to pull the old clutch/pulley assembly and replace it without even opening up the sealed system.


So the load on the bearing when it engages makes it quiet? I would think it would get worse.

 

[punisher]

Originally Posted By: motor_oil_madman

So the load on the bearing when it engages makes it quiet? I would think it would get worse.


Its the bearing that the pulley itself rotates on. If that bearing wears/goes bad it makes noise when the compressor is off, and gets quieter when the compressor engages. Best case, a new bearing or clutch/pulley assembly fixes it. Worst case, the bearing locks up and rips the snout off the compressor.

 

[Kawiguy454]

I bought a pulley/bearing and changed it myself for an 02 f150. that was 5 years ago and still going strong.

 

[Chris142]

Often the bearing gets so hot that it destroys the front seal in the compressor or spins on the nose. Both render the compressor useless. It gets quieter when engaged because the bearings inside the compressor are taking some of the load.

 

[The motor guy]

Originally Posted By: Chris142
Often the bearing gets so hot that it destroys the front seal in the compressor or spins on the nose. Both render the compressor useless. It gets quieter when engaged because the bearings inside the compressor are taking some of the load.


well I hope it will make it for another week or two so I can get it into the shop. I recently found a good shop, but they are usually about 5 business days out. So I don't know if I should get it in somewhere else or what cause I don't want to be stranded. The average person wouldn't even notice the noise it's making so I don't think it's that bad yet.

 

[Brad_C]

Originally Posted By: Chris142
Often the bearing gets so hot that it destroys the front seal in the compressor or spins on the nose. Both render the compressor useless. It gets quieter when engaged because the bearings inside the compressor are taking some of the load.


On that, the bearings in the compressor are not designed to take that load and will wear much faster. This will increase shaft runout which will ultimately trash the front seal. The bearing is a relatively easy thing to change. Do it before you need a whole new compressor.

 

[The motor guy]

Wouldn't it keep making the noise when I shut off the ac completely? It only does it when the ac is on. So basically when the compressor is cycling on and off. IIRC it did it when the compressor clutch was not spinning so I'm assuming that means it was not engaged.

 

[Brad_C]

Your description of the fault is a bit confusing. You are saying you get a noise when the compressor is not engaged, but only if the A/C is turned on?

How does this sound for a theory? :

I've recently fitted a low miles second hand compressor in my car, and the disengagement process takes about 3 seconds. As the coil is de-energised it appears the clutch starts to slip progressively until it is finally dis-engaged. The old one just went click and it was out, this one makes a grinding slipping noise as it dis-engages, but only for about 3 seconds. Once it's out, there is no noise.

 

[JHZR2]

Originally Posted By: motor_oil_madman
Wouldn't it keep making the noise when I shut off the ac completely? It only does it when the ac is on. So basically when the compressor is cycling on and off. IIRC it did it when the compressor clutch was not spinning so I'm assuming that means it was not engaged.


There's still a bearing that lets the pulley turn when the clutch isn't engaged, right? Perhaps when engaged the compressor internal bearings share more load, reducing the noise?

 

[The motor guy]

Originally Posted By: JHZR2
Originally Posted By: motor_oil_madman
Wouldn't it keep making the noise when I shut off the ac completely? It only does it when the ac is on. So basically when the compressor is cycling on and off. IIRC it did it when the compressor clutch was not spinning so I'm assuming that means it was not engaged.


There's still a bearing that lets the pulley turn when the clutch isn't engaged, right? Perhaps when engaged the compressor internal bearings share more load, reducing the noise?


I did say it doesn't make any noise at all when the ac is off completely right? So maybe it's another pulley on the engine somewhere? Like just an idler pulley? Whatever it is it only does it when the compressor is cycling cause I watched the compress make the noise the exact time it cycled on and off.

 

[another Todd]

The bearing that makes noise when the compressor is NOT engaged is the pulley bearing. When the compressor clutch engages, the pulley bearing is no longer taking ANY load, it is locked out and the inner and outer race of the bearing are all rotating at the same speed as the clutch and compressor shaft, it's all one locked unit. When the compressor is NOT engaged, the bearing allows the compressor shaft to stop while the pulley keeps spinning.

 

[The motor guy]

Originally Posted By: another Todd
The bearing that makes noise when the compressor is NOT engaged is the pulley bearing. When the compressor clutch engages, the pulley bearing is no longer taking ANY load, it is locked out and the inner and outer race of the bearing are all rotating at the same speed as the clutch and compressor shaft, it's all one locked unit. When the compressor is NOT engaged, the bearing allows the compressor shaft to stop while the pulley keeps spinning.


So if the ac was off then the pulley would keep making noise right? Cause it stops when the ac is turned off and no noise is made at all.

 

[another Todd]

If the noise is only while the compressor is engaged and turning than the noise is in the compressor, and the compressor may need to be replaced, although, some compressors are normally somewhat noisy so you would have to check with a shop to be sure.

If the noise is only when the compressor is off, and goes away when the compressor is engaged then it's the pulley bearing, and the pulley bearing should be quiet.

 

[The motor guy]

Originally Posted By: another Todd
If the noise is only while the compressor is engaged and turning than the noise is in the compressor, and the compressor may need to be replaced, although, some compressors are normally somewhat noisy so you would have to check with a shop to be sure.

If the noise is only when the compressor is off, and goes away when the compressor is engaged then it's the pulley bearing, and the pulley bearing should be quiet.


I'll just have the shop look at it and tell me what they think cause if it was the pulley bearing then it would make the noise all the time when the air conditioner was off completely. Might just be a tensioner pulley or something not liking the extra strain. I hope that makes sense that the pulley bearing should still be making noise if the compressor isn't on. You see what im saying?

 

[another Todd]

Be aware that the AC compressor runs (in modern vehicles) when the defroster is on. That is to remove moisture from the air before it blows onto the windshield.

 

[Brad_C]

Originally Posted By: another Todd
The bearing that makes noise when the compressor is NOT engaged is the pulley bearing. When the compressor clutch engages, the pulley bearing is no longer taking ANY load, it is locked out and the inner and outer race of the bearing are all rotating at the same speed as the clutch and compressor shaft, it's all one locked unit. When the compressor is NOT engaged, the bearing allows the compressor shaft to stop while the pulley keeps spinning.


I've never seen a compressor configured like that. The pulley bearing allows the pulley to rotate on the nose (the casing extension that holds the bearings and seal) of the compressor, not the shaft, so even when the compressor is engaged the bearing is still rotating. It does this because that honking great bearing keeps the belt load off the compressors bearings and shaft.

In most cases engaging the compressor will quiet a failing pulley bearing because of the extra stability that it receives when the clutch is pulled in, but the bearing is still rotating.

 

[The motor guy]

Well I give up. It didn't even make any noise when I brought it in. It was a pound low so they added some and sent me on my way. They didn't see any reason to do anything else. I hear vehicles squealing like crazy going down the road all the time so I guess I will just wait until it gets to that point instead of looking for problems that don't exist. The noise has gotten much quieter over the last week or so. I use to be able to hear it 15 feet away from the truck.