The blower motor won't move when it should. If I open the furnace and move the fan the motor works for a while and slows then stops. There is a hum coming from the section the fan is in when the motor should be running. Same is true for either in furnace mode or just fan set to 'on'. There's a schematic on the inside panel and a spec sheet but neither of them tell me who made the furnace. Thanks for any help.