AC Clutch noise when turned OFF

[skeeter123]

AC system just started to make this grinding, winding-down noise when I turn off the engine. No abnormal noises when running/engaged.

I have a 2002 Explorer V8, leave it set to Max-AC (fan on low) almost 100% of the time, for past 9 years. (170K miles, no AC probs other than blend-door issues). A few days ago, I pulled into the driveway, and when I turned off the engine, there was a 5-6 second noise as something 'wound down' to a complete stop. Some simple tests narrowed it down to the AC compressor. With engine idling, turn on AC, compressor/clutch activates normally, I can see the clutch engage/rotate, AC works just fine. But when the AC is turned off (either by AC control, or by turning off the ignition), I can see the clutch plate slowing down (not stopping immediately), accompanied by the grinding noise. The clutch plate takes about 5-6 seconds to slow to a stop. I expected the clutch plate to stop right away, but maybe I just never noticed it "coasting" to a stop since it never made this noise before. I've searched this forum, didn't see any problem like this discussed. Anyone know what causes this? I plan to check the clutch gap, maybe take off the clutch plate and see if changing the shims could solve this. Is this a common wear problem at this age/mileage? I would think that if the clutch was worn down there would be more clearance, less likelyhood of rubbing against something its not supposed to. And this wasn't a gradual thing, it started with a loud noise and continues to do it. Any advice is appreciated.

 

[skeeter123]

OK, so I got a bottle of R-134 and tested the low-side pressure (with the built-in gauge), it was a little low according to the scale on the bottle's gauge. Note this is the first time it's ever been checked/re-charged in it's 170K life. I charged it from the bottle, it took about 1/2, maybe 9 oz (it's hard to judge just holding/shaking the bottle). Measured the temp, system puts out 47-deg AC when its 87-deg outside, seems OK to me. But it still makes that winding-down noise, like one of those wheel-of-fortune's at the county fair, winding down to a stop in 5-6 seconds. AC works, but I have a bad feeling about this noise, it never did it before, doesn't sound like its going to last. I want to figure this out before it dies, I suspect the clutch, but the clutch "works" when its on, just makes noise when it's turned off. Also, if I turn it on for only a few seconds, it doesn't make the noise; if it runs (clutch engaged) for 20 seconds or more, then it'll make that noise when turned off. I have no AC experience obviously, any help would be appreciated.