I have been working on the same problem myself. I have a 99 GS400 and when I turn the A/C on the compressor kicks on for a few seconds and then kicks off and my A/C light starts flashing. My problem comes and goes. It only seems to do it when the car has been sitting in a hot parking lot all day. Normally in the mornings or in the cooler months I have no problem. I took it to my local dealer and of course it would not do it in the morning, so they had no idea and charged me $50. I have done a lot of research and I can tell you this. There is a rotation sensor on the compressor or what the manual call a lock sensor that monitors the RPM's of the compressor and compares it to the RPM's of the motor and if the difference is to great the computer assumes that the compressor is locked up and the belt is slipping so it disengages the clutch. These are some of the things I have checked. Ohmed lock sensor OK, checked plugs and wiring OK, Checked charge OK, Replaced belt Still NG, checked all pulleys and tension-er OK. To make sure my belts were not slipping I used some belt dressing and then put a wrench on my tension-er and gave it some extra force and still no good, I used brake cleaner and cleaned my clutch still N.G. If I jump the clutch it will blow cold all day. The only other things I can think of is something is causing to much pressure on the high side locking up the compressor and causing the clutch to slip??? or maybe something else. I hate to replace my compressor and that not be my problem.
