I have a 2009 Gen II Prius. Yesterday, the air conditioning shut down (warm air out of vents) while driving. Restarted iteslf 25 minutes later. Took the car to the dealer, they found nothing. I always hate it when mechanical systems fix themselves.
There was a problem I had with an older Camry that did the same thing. It turned out to be an a/c relay that had some sort of fault, I believe an overheat situation. Dealer could not find it either, but after I did research on the good ol WWW, i discovered it.