A method for controlling an air conditioner and an air conditioner are provided. The air conditioner may include a compressor that compresses a refrigerant; and a control unit that controls the compressor. The control unit may include a main control unit that controls an entirety of the air conditioner; a start-up control unit that controls the compressor at an initial start-up of the compressor; a normal control unit that controls the compressor according to a target room temperature after the start-up control unit completely controls the compressor; and a bumpless control unit that calculates a compensation value for lowering an operating frequency of the compressor according to an indoor load when a priority for controlling the compressor is transferred from the start-up control unit to the normal control unit. The bumpless control unit lowers the operating frequency of the compressor according to the compensation value.