I just had my compressor replaced. The old one had a very slow leak. I recently had the system recharged and it was blowing 41F air, but the shaft seal was shot so I went ahead and replaced it. The new compressor has a more pronounced sound to it (OEM, new, not remanufactured) . The sound only occurs when the compressor engages and is best described as a high-pitched moan. The old compressor had its own moan about it but it was softer, not as high pitched, and not as intrusive into the cabin. I am thinking of having the shop put a different one in. Any thoughts on what is causing this sound? The AC is working fine, but this new noise is bugging me. I also noticed that when this compressor cycles on it pulls the engine idle down about 200 rpm. Is this normal? I never noticed how much the old one did this so I have nothing to compare to.

 

Either your idle air control valve (IACV) is not compensating for AC compressor load, or the load is excessive. Excessive load can result from an overcharged compressor, inadequate lubricant leading to compressor friction (damage it won't last long), or simply bad compressor. There are brands of aftermarket rebuilt compressors that have a terrible rep for out-of-box failures and poor performance. If you have your old compressor, you might consider replacing the shaft seal and reinstalling. Shaft seal can be purchased from ackits.com.

Check IACV by observing rpm at idle (AC OFF) and when you place car in gear and hold the brake. The idle speed should stay constant as the IACV compensates for the transmission load. If it drops 100-200 rpm, the IACV, IACV passages, and throttle body may need cleaning.

good luck