I had never heard of P0483 (Cooling Fan Rationality Check Malfunction) before, and it looks like a code that varies somewhat from vehicle to vehicle. In a Dodge truck forum it was pinned down to a bad electro-viscous fan clutch. About all I can determine is that the ECU is unhappy with the way the cooling system responds to automatic controls. The Focus has a very active cooling system control strategy, much more sophisticated than the old “hope it doesn’t overheat… tell the driver if it does” system. Part of that is not working as designed, and I’m afraid this may be a job for the dealer. EDIT – after sleeping on it, I am thinking the “short cycling” of the air conditioner may have caused the condenser fan to cycle too quickly, confusing the ECU. I suppose you have tried resetting the code, so I’m out of ideas again.
It looks like you have a faulty radiator fan. The cooling fan is a device for blowing air around the radiator and engine. The car is cooled in two ways: liquid and air. The fan belongs to the second. It does not work constantly, but only when the motor is very hot. How to choose the right fan? Check cooling fan manufacturers for details.