99 Lexus RX 300, v6,90k miles. a/c comp. is humming only at stops and park. while driving its ok.cools fine. had belts changed not too long ago. maybe over tightened, maybe over charged, undercherged, maybe cooked. what do you guys think that might be?

What's needed is to know if the humming is while engaged or not as the fix would be different. When off the compressor is really just a pulley (clutch that has a replaceable bearing)

It's also possible that the noise is another pulley just acting up with the load of compressor being on if so.

I behooves you to tend to this real soon as if it indeed is the compressor, pressure taken and within specs, fixing it now will save both money and aggravation for the best fix,

T

PS: If compressor itself it's better to disable it now if you need to buy some time. Allowing it to fail could disable use of the car as a whole!
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Tom Greenleaf - MetroWest, Boston