A shaded pole motor uses a start capacitor to give the needed boost for start up. This is measured at 10X RLA (run load amps) and is normally a momentary amp draw. However with age the poles and armature can get weak at specific points and not have enough umph to get the fan moving. I would get someone to look it over and replace the blower motor. What is strange about this is there are internal overloads in the motor that should catch this and stop the high current draw long before the breaker trips. This could be a much larger and more dangerous issue requiring professional intervention.