I don't believe it ever actually locks up. Get it hot and running at idle then cut it off the fan should stop with in a few seconds or a few rounds. With the engine off but hot, spin the fan be hand, it should have a reasonably amount of resistance and it should only spin about 1-1.5 rounds when you spin it with some force. With the car off grab the fan and check the bearing for slack. If it fails any of these I would replace it.