I have a similar problem on my 94. What I have found out is that dust and
debris gets down into the evaporator core which in turn rots it out. When
this happens the system is not able to hold the pressure it needs to keep
running and shuts down the compressor. You probly need to find a reliable
shop near by and have htem check it out. It may be as simple as a pressure
sensor or it could be the evap core.

There are a couple of things that are likely.  There's a temperature
switch on the back of the compressor that cuts the A/C off if the
compressor gets too hot.  This seems to be set too conservatively, and
is not present on later cars.  Just bypassing this switch may get rid of
the problem.  The clutch on the compressor seems to have trouble
re-engaging when it is hot, and rewiring with a relay seems to help in
this case, as it eliminates the voltage drop in the A/C circuit.