850 Air Cond./ Not superheat problem

'94 850, standard A/C.

Most times, the A/C works fine, and cools well. Occasionally, the compressor does not run. When this occurs, the blue indicator on the dash does not light.

Most often when it fails to work the car has been driven, shut off, (sometimes for just a minute or two, sometimes for 1/2 hour or so) and when restarted, the indicator lights for perhaps two seconds, goes out, and the car will not cool.

Yesterday this occurred, and fiteen minutes later, driving with the windows down, I felt a blast of cool air, and saw the indicator lit. The A/C worked well the rest of the way home.

Two things to consider:

2) The R134 charge is 'normal' per my cheapie suction-side guage/filler.

I suspect something is getting heat-soaked, and failing, but I don't know what I might check before sending it to the repair shop.

Any ideas?

Thanks!