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AC Compressor-Unusual Noise

Had ac compressor replaced on 2002 Toyota Camry V6 at a shop that works only on imports and has been in business 30 yrs. New compressor ran and cooled well. When inside car and compressor engaged, there is a humming/whinning/cooing noise that speeds up/down when accelerator is pressed/released. If I click compressor off or it disengages, you cannot hear noise. The noise can be heard from outside when compressor is engaged with hood up but it’s not as loud (I think running engine is muffling some of noise)and can’t tell where it’s coming from. I took it back to shop. He could not locate exactly where it was coming from. Said he took serpentine belt loose and checked pulleys. He did not think it was the new compressor but did decide to get another compressor. Second one runs and cools good but there is still the same noise. He let me listen to the new compressor and existing alternator with a mechanic’s stethoscope. Compressor sounded smooth when engaged but the alternator was much louder through the stethoscope when compressor engaged. He now thinks the noise is coming from the alternator. Again, with hood up and compressor engaged, you can’t zero in on where it’s coming from. He thinks the new compressor when engaged is putting more of a draw on the alternator which has a 170,000 miles on it. I asked if he was telling me that I needed a new alternator. He said no as far as functioning of it. But if the noise is coming from it, that’s the way to get rid of noise. I was referred to this shop by three different people I work with. Has anyone ever ran into such situation and what is opinion.

170k miles on an alternator, even on a toyota, is a lotta miles. It sounds like one of the bearings is starting to go on the alternator, there are two of them, one front and one rear, and when they go they let you know with a noise that gets worse and worse till you just cant stand it. Alternators are not all that costly, so at the risk of “throwing parts at a problem” I would go ahead and replace it now.

I could be incorrect, but I believe your serpentine belt drives both the alternator and the AC compressor. If so, depending on the routing the AC clutch engaging the compressor and thus putting more load on the belt could be putting more lateral load on the pulley of the alternator. That could cause worn alternator bearings to become noisy. The “draw” electrically would be insignificant.

Has he (or you) tried releasing the belt tension from the alternator and turning as well as axially & manually wobbling the alternator pulley?