I'll throw this in. May be worth looking into.
I do not recall the official part name, but on the compressors that are mounted in the M103 cars(serpentine belt model), there's a sensor on the compressor that detects excessive belt slack. If it's determined the belt is too loose, it will shut-off the compressor. In other discussions at this site, people have said that one way to detect this is happeneing is to pull over, turn off engine; then restart. Compressor should come back on. If this is happening, this may be your problem.
In one other post here(way back when-do not remember the date), a pro indicated that this sensor can sometimes deactivate the compressor even with correct belt tension...faulty sensor? Sounds like it.
My 2 cents.