If you have a set of feeler guages (as for valve adjustments) check the clutch gap on the compressor. The spec is 0.50mm, plus or minus 0.15mm. In my limited experience, once the gap reaches 0.80-0.90mm the engagement becomes flaky. Excess gap is particularly suspect if it works fine when the car is started cold, but then stops after a period of time.

Grease/oil on the clutch surfaces can cause enough slip to trigger the cutout. An easy/cheap fix is to degrease it. Use anything from brake cleaner to simple grean. Just soak the area of the clutch gap, wait, rinse with water if necessary. Some folks have had this treatment cure their ills.

- JimY