A/C intermittent on hot days

Recently, my car has been having intermittent A/C problems. Whenever the outside temperature is over about eight five degrees F, the compressor will turn off. I will be driving along, everything is fine, then the vent air starts to warm and I can smell the condensation evaporating off the coils. It will stay off for in excess of ten minutes. I have observed it not working for over an hour. Parking, shutting down, removing key, and restarting has no effect.

I took it to the dealer and they evacuated it, refilled it, "replaced a relay", and charged me $400.00. Had no effect whatsoever.

I took it back today and they said I needed a new condenser coil, evaporator coil, and compressor clutch. I sense that they have no clue what is going on.

Suggestions?

Thanks in advance!

P.S. - I do not have much experience with car repair, but do electronics work. I know my way around a circuit board and understand general engineering/mechanical principles.