[rohrmann]

Sounds like the blower motor is shot, or at least the bearings are bad and causing drag which causes higher amperage which melts the fuse. There should be a manufacturer data tag inside which will give you model number and from there you can find a manual and what part number the motor is. It might also give you instructions how to replace the motor. If the motor isn't available, you would then have to start looking at a replacement furnace.