This is a new installation. Most of the duct size is 10". The initial duct stub up contains 2-22.5 degree bends from the Elite hood insert. It passes through the cabinet and into the attic. It is 8" duct. Once in the attic it is transitioned immediately to 10". There are 2-90 degree bends coming off the stub-up, then another as the duct terminates into the inlet side of he blower. On the outlet side there is one more 90 degree bend and a 45 as the duct terminates into the china cap. When the rheostat is initially set on low, the motor just hums, it isn't until it is given full amperage that it begins to blow. Any setting other than high stalls the motor and it just hums. Is the problem the motor, the capacitor, the rheostat or the duct?