My swamp cooler is leaving everything in the house black, why?
It is my experience that the bolt pattern used to mount the motor in a swamp cooler can easily allow the motor axis to be set not parallel with the axis of the fan shaft. When not aligned parallel the pulley on the motor, even when appearing to be lined up nicely with the fan pulley, can end up rubbing excessively on the sides of the drive belt. This can create excessive amounts of black dust as a belt wears. It is even more interesting that a new belt can be more subject to getting chewed up like this than an older used belt that has developed a glaze on its surface.