If your vehicle has an electric fan, then it will always kick on when you turn the a/c on. If your car has a clutch(mechanical) fan then it will only spin as fast as your motor. That's why people say not to leave the a/c on if your car is in park, cuz the clutch fan at idle isn't pulling enough air thru it to cool it down. It can actually make your engine overheat, had a close call with my truck from the same thing.
There is, however, a certain degrees that the electric fan kick on. Not sure on the temp but my guess would be a little above or around 220