I will keep the relay in mind as a possibility.
I had to replace the serpentine belt 8k miles ago due to oil from the vacuum pump. I don't imagine oil would be causing the belt to slip, since I hear nothing, the belt is tight, and everything appears to be clean
I also plan to replace all fuses in the fuse box with a new set I have in the glovebox and keep the old ones as spares.
Also, this only seems to be happening when it's really hot--the time I need the AC! Today I drove the car hard up and down hills in 70 degree weather and the AC cooled great--everything worked like a champ. Wait till it gets warm and the AC stops working.
The compressor clutch gap, when I look down from the top, appears to be 1-2 mm.
Does the aux water pump cause this, or does this occur only when the heat is on?