A/C diagnosis/repair, DIY?

The A/C in my truck has never worked since the day I bought it, which is over two and a half years ago. Presumably the system is empty (R-12 printed on the compressor). Is there a way I can tell if the compressor is good
myself, rather than take it to a shop? If the compressor is blown then to hell with it, maybe someday I'll find a good one at a junkers. In the meantime I'd stick a sunroof in it instead. The clutch works, as I discovered yesterday when I applied +12v to the green wire ontop of the compressor. Any ideas? Thanks.
'91 T-15 Jimmy, 4.3L TBI, 700R4, rusting a little more with each passing day.
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Sorry to hijack, but I'm having A/C problems on the same truck, 3 years newer, with a CPI engine. I didn't see any sign of leaks, but the lower hose to the condener looks like it has a peice of rubber hose just slipped onto the ends of 2 metal lines near the radiator, kinda like you'd do to repair a leaking tranny cooler line, cut the leaking section out, flare the 2 ends and put a peice of rubber hose on there. Is that supposed to be? This is the line directly between the evaporator and condenser, the low side I suspect. I don't see any signs of leaks, haven't tried jumping the compressor to see if it runs. Any other thoughts? I'll be taking a couple 3+ hour trips this summer and would like to use A/C instead of 4x75 venting. I might just take it to the shop that last did work on the A/C system, point that one spot out and say it doesn't look right. My system is still an R-12 system, and I'd like to keep it that way, when it works it blows COLD.
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The accumulator has a pressure switch, looks like an oil pressure sensor. Unplug plug, and use a short heavy jumper wire to bypass switch, now try compressor, just a short burst please ! The switch keeps the compressor from engaging if the freon pressure is too low. Without this switch, the compressor would burn up, due to poor / no oil flow. Assuming the compressor starts, and sounds OK with switch jumpered, you could simply be low on Freon, or you have a leak. If it were my truck, I'd convert to R 134A. Much cheaper in the long run, if you plan on keeping truck a long time. Post back if you need more info on the conversion.
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