Whining noise from engine when Air Compressor is on. Gets louder when accelerating

[Aveoon]

As the title depicts, when I accelerate the whining noise gets a bit louder. It almost sounds like a barring or belt. But the noise is ONLY being made when the AC compressor is on. It will go away immediately once I hit the ECON button of the OFF button on the AC controls. I've also had, hopefully related, problems with the AC working intermittently. The compressor will shut off and the air will come out of the vents with a little less force than normal.. Lately, it seems to be fine, but the compressor will sometimes shut itself off, then come back on later in the drive. I cannot pin point when this is happening exactly. But in one case I noticed that the compressor came on (full blast) even though I had the ECON switch on.

I'm not sure if these problems are related, but definitely the whining concerns me more. I'm not sure what other details to include, so let me know if I'm forgetting anything.

my Car: 2004 A4 1.8t quattro manual. Water pump/timing belt changed recently, not sure about serpentine belt (didn't have record from previous owner). things also changed recently, that could possibly be related: coolant sensors (both of them), almost all of the pluming (hoses), and various other odds and ends.

[robertbutnar]

sounds like its time for a new serpentine belt, maybe the Tensioner as well.

[vjborelli]

I'd say either belt, tensioner, or idler roller. To be on the safe side, have your AC system checked for prop per pressure.

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[old guy]

Unfortunately I think a new compressor may be in your near future. The AC compressor is a variable output pump and it is engaged all the time whether or not you hit the econ button. Yours is making noise when under load and it starts compressing the refrigerant. That coupled with your occasional AC performance issues points more toward the compressor than the belt tensioner.

[vjborelli]

Unfortunately I think a new compressor may be in your near future. The AC compressor is a variable output pump and it is engaged all the time whether or not you hit the econ button. Yours is making noise when under load and it starts compressing the refrigerant. That coupled with your occasional AC performance issues points more toward the compressor than the belt tensioner.

So our compressors don't use a pulley clutch to disengage?

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[old guy]

So our compressors don't use a pulley clutch to disengage?

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No they do not.

[Aveoon]

Thanks for the tip,

Would you suggest any surefire way to test it?

[vjborelli]

No they do not.

Alrighty.

Any suggestions on a new compressor OG?

I've had the car about 7 months, AC worked fine all summer. And without any warning, it stopped working 2 weeks ago. I checked it out, and I've got a bolt on the front (behind the pulley) sticking out and a 3 inch crack along the bottom.

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