Barkydog is correct; the blower motor is drawing too much current. Odds are if you connected an ammeter to the blower motor you would likely be shocked at the amount of amps being pulled by the blower.
The blower motor is not that much and the blower can appear to work fine even while drawing an inordinate amount of amperage.
Some years ago my wife came home one day and said the blower in out Lincoln had blanked out temporarily. When checked, it appeared to work fine and made zero noise. With an ammeter connected that blower motor was pulling 27 amps on the HIGH setting. That is a godawful amount of current even with a 40 Amp Maxi fuse in place. With a 27 amp steady pull one can safely figure (as with anything electrical) a 50 amp surge current.