[Richard]

Hmmm, it does sound like a lack of electrical motivation.

So, you are saying it worked, then it didn’t, then it does, then it doesn’t.

When you remove the top of the dash can you see the backside of the heat/ac controls? If possible determine if you have power to the backside of the fan control. If you do, then I would replace the switch, If not, then somewhere between the switch and the fuse panel is the culprit.