Engine noise with A/C On when turn off engine?

[MoparDave]

Ok I need some advice finding this noise in the serpentine belt / Accessory area. This is not the normal squeal from the belt but does happen when the engine is turned off. Only happen if the A/C is on. I am unable to recreate the noise by turn the A/C on and off with the controls and I do not hear the noise under normal driving. When I turn off the engine and the A/c is on I get a metal to metal sound like a dry part is coming to a stop. I have used my statoscope and listened to the tensioner, idler pully A/C compressor and PS pump all as the engine is turn off and cannot find the sound of the noise. The fan clutch does engage and is running when it happens but I just can’t seem to pin point the noise. Any ideas?

 

[Motorhead]

I believe what you are hearing is the residual high side pressure from the A/C compressor going through the orifice valve

 

[MoparDave]

I do not think its A/C high pressure but that something to check.
I'm starting to think it may be that over running clutch in the alternator.
The extra load from a/c compressor it making it jump. Just something I'm looking into

 

[NavyDood]

Ever since I first started driving 20+ years ago, I have always turned the A/C off prior to shutting the engine off. I even do it in our brand new Mazda 3i SkyActiv 5dr. Dunno how or why I started that back in the day, but it only makes sense to take the load off the compressor prior to shutting off the engine.