Disclosed are an air conditioning system and a method for controlling an operation thereof, whereby a charging device for charging power to be supplied into the indoor unit is employed, a chargeable control unit is separately employed, or a separate control unit connectable between the indoor unit and an electronic expansion valve is employed, thereby closing the electronic expansion valve even if power supplied into the indoor unit is blocked while controlling opening and closing of the electronic expansion valve, and additionally preventing the electronic expansion valve from being left open, resulting in prevention of an overload of a compressor within an indoor unit.