Air conditioner, and method for controlling an operation of the same, the air conditioner including a sheath heater in the accumulator for heating the refrigerant in room heating for delaying deposition of frost on the outdoor heat exchanger. The sheath heater includes a coil formed heat generating part, and two electrodes connected to the heat generating part for supplying power. The method including the step of varying the heat generating rate of the sheath heater with an exterior temperature or a capacity of the indoor unit, thereby delaying deposition of frost on the outdoor heat exchanger.