| 摘要 |
A load current value I of a motor (4) rotationally driving an impeller (3) is read out when the impeller (3) is rotated at a predetermined set rotational speed X 0 , and the rotational speed of the impeller (3) is increased so that the load current value I becomes equal to or larger than a threshold value I 0 when it is determined that the load current value I is smaller than the predetermined threshold value I 0 . |
