Disclosed is a method for operating an air conditioner which is basically composed of an outdoor unit and an indoor unit and whose operation is controlled on the basis of values measured by a plurality of temperature sensors. When any one of the plural sensors is disabled due to wire disconnection, short-circuit or like trouble, and when a specific sensor which has a complementary relation with the disabled sensor with respect to the heat cycle or which has an object of measurement substantially the same as that of the disabled sensor is normally functioning without any wire disconnection, short-circuit or like trouble, the value measured by the specific sensor is based to presume the value that will be measured by the disabled sensor if the disabled sensor functions normally, and the operation of the air conditioner is continued on the basis of the presumed value.