I would first of all increase the fuse to 20 amps to see if it holds. If there is a major short occuring it will still give you enough protection. If it holds you are away to the races. Since you saw a refference to a 25 amp in that curcuit there may have been a revision of the blower motor during the production run at some point to make it a little stronger. I would do a little research on that. Were the part numbers on the old and new motors the same for example? your new motor could also have a defect as well. Or a bare wire might be intermittently shorting in the circuit for example.