To determine a position of a flap in compliance with a performance of a motor in a product by a method wherein a time ranging from a reversing time of a limit switch to the next reversing time is calculated for every product and a stopping position of the flap is determined on the basis of this calculation.

After starting an operation of an air conditioner, a flap 14 returns again to F1 through F1 to F5. A part F1 in which a limit switch 24 is changed over from its OFF state to ON state and a part F5 in which a limit switch is changed over from its ON state to OFF state are monitored and measured during a time T required from F1 to F5 and they are counted and calculated. Then, the time T is divided by the number of stopping positions of the flap 14, for example, in five steps ranging from F1 to F5, the time required for each of the intervals is stored as T/4. In the case that the flap 1 is desired to be fixed at the position of F3, the stopping position F of the flap 14 is set during an operation of an air conditioner, a T/2 second of value of flap fixing position becomes a driving time for the flap motor 22 after sensing F1 and it is fixed after completion of a timer count.