When the door to the balcony is open the A/C is turned off by a proximity switch that is magnetically switched at the door. It's the same as the magnetic sensors on home doors and windows for the security system. The switch is mounted on the door frame and the magnet on the door. When the magnet (door) is next to the switch the switch is electrically "closed" and the A/C is energized. When the door opens the magnet no longer "closes" the switch and the switch opens, thereby de-energizing the A/C.
If you put a magnet next to the switch the switch "thinks" (if you will) the door is closed and the A/C is powered. This way you can have the door open and still have the A/C running in the room.