You have a two-speed electric fan setup. The low speed setting is triggered by the air conditioning, based on a certain pressure reading. I don't know what that pressure reading is. The high speed setting is triggered by coolant temperature reacing 105 degrees C.

I don't know about one fan speeding up from the low setting when the other is disconnected. Perhaps that is a safety mechanism to help keep the car from overheating with the a/c on?