An analog-to-digital converter has a digital-to-analog converter, first, second and third comparators, and a sequential comparison register and control logic circuit. Due to the foregoing, as the packing member is an elastic body, even if the packing member comes into contact with the door shaft or the bearing hole, the door can be rotated. At least one persistence counter notifies the controllers if excess loading conditions exist on the blade motor or traction drive motor. The accessibility of many testing methods allows quick location of root cause failures, which allows improvements to be made to the manufacturing process.