To permit defrosting operation optimally in accordance with the condition of environment, in which an air conditioner is provided, by a method wherein the air conditioner is provided with a control means, controlling a four-way valve based on a defrosting operation condition, regulated by a defrosting operation regulating means, to effect the normal operation or the defrosting operation of the air conditioner.

When a normal power supply is impressed on an air conditioner, the air conditioner is initiated by the control signal of a control unit 520 and a defrosting operation regulating means 510 is adjusted by an expert in accordance with an environmental condition upon manufacturing or installing the air conditioner. Next, a defrosting operation temperature changing regulator 512 as well as a defrosting operation time changing regulator 514 are checked to set the defrosting starting temperature and a defrosting operation time of the air conditioner by the regulated defrosting operation temperature and the defrosting operation time. Further, a defrosting operation pattern changing regulator 516 is checked to set the defrosting operation pattern of the air conditioner and effect the defrosting operation by the regulated defrosting operation pattern.