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AC Compressor-Peculiar 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.

I posted this last week and received some suggestions. A couple of folks suggested alternator-unplug and see if noise remains and another suggested bearings. I went back to the shop this am. The mechanic did unplug and test and noices remaines. He also took a large screwdeives and tried to change leverage during compressor engaged and running. Did not affect the noise. He said last week he thought it might be the alternator. He now is not so sure but does not want to change it just to change it and see what happens. He wants to solve the mystery even thought he says it still might be alterator. He is aggrivated that he hasn’ been able to figure out yet. As I stated in post above, he has been in business 30 years and said he has never ran up my situation. Anymore suggestions?

The mere act of releasing and replacing the drive belt to replace the compressor might have been the last straw for the possibly fragile alternator or belt tensioner.