An air conditioner includes a compressor, an outdoor heat exchanger, an indoor heat exchanger, a converting unit, an accumulator, and injection module, a supercooling valve, and an injection valve. The injection module expands and vaporizes a portion of refrigerant flowing from the indoor heat exchanger to the outdoor heat exchanger in the heating operation. The supercooling valve is disposed between the injection module and the accumulator and is opened to direct the portion of the refrigerant vaporized in the injection module to the accumulator in the heating operation and then closed after a predetermined time passes. The injection valve is disposed between the injection module and the compressor and is opened when the supercooling valve is closed in the heating operation, thereby injecting the portion of the refrigerant vaporized in the injection module to the compressor.