A method of controlling an air conditioner includes determining whether or not a signal for operating the air conditioner is input to a controller. When it is determined that the signal for operating the air conditioner is input to the controller, determining whether or not conditions for variably controlling the air conditioner are satisfied. When it is determined that the conditions are satisfied, an energy flow mode is checked on the basis of an energy flow between a battery, a motor, an engine, and electric components. The air conditioner is controlled in a mode corresponding to the checked energy flow mode.