I believe that there is an electronic fan speed control circuit module which is mounted on a heat sink which in turn is mounted on the actual blower motor. As stated in the previous post, your intermittent trouble is not likely to be a fuse. I'd suspect the motor brushes, the speed control circuit module, corroded wires / connections and finally (gulp!) the HVAC computer itself. I can't think of any easy way to trouble shoot this. You're going to have to get a look at that motor. If it is brushes ( they'll be worn down to the springs ), I'd take it to a electric motor rebuild shop. That'll be a lot less expensive than replacing the entire blower motor with an OEM new one. Hopefully, someone else in this group can advise you on how to get to the motor. Good luck.
Resistance is Futile.