The invention relates to the technical field of air conditioning, and provides an air conditioning system, air conditioner and air conditioning method. In the air conditioning system a compressor shell is provided with a heat storage device and an electrical heater. The outlet of the compressor is connected with the inlet of a first Tee valve. The first outlet of the first tee valve is connected with the first connection terminal of a four-way valve through a first pipeline. The first pipeline passes through the heat storage device. The second outlet of the first tee valve is connected with the first terminal of the four-way valve through a second pipeline. The second and third terminals of the four-way valve are connected with an indoor heat exchanger and an outdoor heat exchanger respectively; the fourth terminal of the four-way valve is connected with the air returning terminal of the compressor. According to the air conditioning system, the heat storage device preserves the exhaust heat of the compressor shell. Combined with the electric heater the temperature in the heat storage device can attain the design requirement. In the heating mode the outflowing coolant passes through the heat storage device to rise the temperature at first and to make sure of the stability of the defrosting process. The defrosting rate of outdoor machine is accelerated. The heat comforts in the room under low temperature heating can be improved.