There's a wire that drives the compressor clutch directly (via a relay).

a) Apply +12V directly to the nearest connector. You should hear the clutch
click in.  If so, you could then run the engine and do the same to see if
the AC starts to work.

If not, you need a new compressor clutch. More likely is one of the
following.

b) the AC has a dual or triple pressure switch that disables the compressor
if the refridgerant pressure is too low or high. Look for a switch device on
the drier or on one of the tubes. Pop the connector and jumper it. See if
the clutch kicks in. See idea of a).

c) compressors have a hi temp cutout switch too. Look for a wire, and test
the switch with a meter.

d) There's going to be a relay or two that runs the AC fan and drives the
compressor clutch. Look for a secondary fuse or relay box.

e) Was the AC empty or just low on refridgerant? If it was completely empty,
you can't just refill it without vacuuming out the system. It might for a
while, but will run hot (and eventually stop working) because the air in the
system compresses more than the refridgerant.

Stewart DIBBS