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Weird air conditioning problem, any AC guys on here?

streetroc

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So a few months ago I rebuilt the air conditioning system on my Honda Accord. New compressor, accumulator, expansion valve, o-rings, and condenser. I filled it with the correct amount of PAG oil and then had it professionally evacuated and recharged. It works great now and blows very cold. However sometimes when the compressor turns on at 2-3000rpm it makes a really weird howling/whistling/squealing noise. The only way I can describe it is that it sounds like a midget is inside the glove box f***ing a goose with a kazoo. I'm pretty sure it's coming from the expansion valve on the evaporator core. It's like when it releases freon with the engine turning at a certain RPM there is some kind of a harmonic resonance reverberating through the lines. It only does it some of the time and if I push in the clutch and let the engine go to idle it immediately goes away. WTF is going on here?
 
Probably a vacuum line going to the blend doors or similar door actuator.

Going to idle would not impact the ac compressor, it would, however, change the vacuum setting in the vehicle.

Nope. Actuator doors are controlled by an electric motor. It is definitely dependent on engine RPM while the compressor is engaged. And it's not constant. It comes and goes
 
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