Dying A/C Compressor Clutch?

[Louisville86]

I have a problem with my A/C compressor clutch on my '86 (2WD, 2.9L). I noticed that the freon seemed to be low, as the compressor was cycling on and off (on for maybe 10 seconds, then off again). So I took it to the shop, where they evacuated the system, added a pound of (R-12) freon (it's $99 a pound now, ouch). It worked good last summer; I had it fully charged two years ago, so I figured a slow leak is something I can live with.

Sounds good, the shop guy says, it's coming out of the vents at 45 degrees. Great, I say. I drive away, turn the A/C on and I hear a terrible clunk/grind, but the compressor goes on and it gets cold.

After yelling at the shop guy for not testing it and giving it back to me (after I paid), I investigated further, and when it's been sitting for while with the A/C off, it clunks/grinds for a second, and even puts out a puff of smoke. When it's idling with the A/C on, it sort of chatters. When I'm driving, it gets sort of "growly," but stays cold.

So, is my compressor clutch fried? Or worse, is it the compressor itself? Was this brought on by fully charging the system? Should I try to replace the clutch and keep the system charged? Can I do this myself? I'd hate to lose the 2 pounds of R-12 in the system. Here is what the labels on the back of the compressor look like: it's definitely two different (Nippon Denso) assemblies (yellow is the compressor, green is the clutch).

And the general compressor layout. Belts, etc. are in good shape.

 

[Louisville86]

No advice, anyone?

Update: it seems to be the compressor that's noisy, so I will probably have to tackle that. It's noisy but it's still cooling well. I suspect that it was overcharged by the dumba$$ mechanic's assistant; I should have stayed and watched him work.

At this point I probably will get a compressor from the salvage yard (or even a new one) and make the jump to R-134. I won't pay $99 every other year for A/C and the newer refrigerant only means a few degrees in terms of cooling loss. Lucky that the single cab is very easy for the A/C to cool and Colorado is not brutally hot in the summer.