Well, if it were an air conditioner I'd suggest the start capacitor, but DC motors do not have those as a rule. The suspects are...
Voltage to the blower (Bad connection, bad relay on control board) and this one may surprise you (I know it did me) Bad wire, and bad motor, (Lubrication of the bearings if possible may help) .
Oh,,, One other thing: WHEN the control board fails.. (Hopefully years from now) consider Dinosaur Boards as a replacement.. .here is what I found when mine failed
OEM (Very slightly rounded) 250 (cheapest I found was like 245 plus S&H)
Dino, Total price, SH included 108
I have some experience in electronics, Ham radio operator, certified technician. Opening the box and putting eyes on the Dino board I was seriously impressed with the quality.. On a closer look the design also impressed me.
I have a theory as to what killed my OEM board.. It appears Dinosaur Boards shares that theory since they added protection against.. Just that failure mode.
I do NOT expect to have to replace this board. Ever.