[olddog]

The numbers you got seem reasonable and a slow blow fuse should take the inrush, providing the fan is not turning on and off frequently. That said, I suspect if you were measuring the current when the fuse blows, it would be headed for infinity, do to a short somewhere. Or the fan, may have a bearing seizing. It would be nice to hang an amp meter that would store the peak amp draw, to prove I am right, cause I am wrong from time to time.

You might try following the wires from the fan and see if they are getting too close to something hot or rubbing on an abrasive grounded surface. You can often see where it arced.

Good Luck.