Help with A/C diagnosis?

Hi all

1996 Chevy Silverado 1500 w/Vortech 350

Just warmed up enough here to turn the A/C on for the first time the other
day and it blew hot. It was working fine last season, so I figured it just
needed a recharge.

I bought a kit with the hose, gauge, and can of refrigerant. Everything
seemed pretty straightforward. It said if the compressor didn't run, to
empty the whole can into it, it said it would only fit one valve, and it had
green (low), blue (filled), yellow (alert), and red (danger) zones.

I start the engine, and sure enough it's in the blue. Compressor not
running.

Attach the can, open it up - goes instantly to red. turn off can, back to
blue. Turn it on, back to red, off - back to blue. I'm sensing a pattern -
just let it fill for a while.

It fills and fills and fills - still nothing from the compressor. I start to
suspect something electrical.

After about ten minutes - the compressor comes on for about 2 seconds.
Well - it's not electrical.

I turn the can off and take a reading - there's a pattern. The gauge goes up
to nearly the yellow zone in the green, the compressor comes on for two
seconds, knocks it to the blue/green borderline, pressure builds back up to
the green yellow line - repeat. Basically the compressor comes on about 2
seconds out of every 15.

I disconnect the can - it's about 3/4 full!

I try adding a bit more - doesn't seem to take it - and the connector
"spewed" when I disconnected the hose.

I realize now I'm probably not looking at a DIY repair. It would be NICE if
I could fix it, as I'm driving 5 hours tomorrow. But mainly at this point
I'd like to have an idea of what to expect at the mechanic - what to say or
what not to say - what to expect, etc.

I have a feeling I shouldn't even mention I tried to recharge it. "Uh - no -
of course that didn't work, because you need a whole new system". I just
don't want to walk in somewhere looking like a gaping billfold to someone.

Any ideas what might be going on - what to expect, what to say?

Can I assume, A) it's charged, B) it's not electrical, and C) the
compressor's not frozen up?

Thanks for any input!
Kevin