I'm having a bizarre issue with my HVAC forced air blower motor. Specifically, it will not start and just buzzes while showing a great deal of startup current (20-22 amps).
Background: This is a TEMPSTAR Model# NUG5150BKA1 furnace that is ~8 years old. I purchased the home last December, and I noticed back then when the blower fan would turn on, I would hear a loud buzzing sound for 1-2 seconds and then the fan would kick on. When the old motor failed a few weeks ago, it was just buzzing continuously for a minute and by the time I ran downstairs the motor was smoking.
A friend and I just replaced the motor with an equivalent new model (same brand - FASCO). We went through the entire wiring and verified to the best of our ability that it matched up with the wiring diagram on the blower door. When we power on the system and have the thermostat call for cool / cycle on the fan, the motor BUZZes loudly and will not turn over. A clamp ammeter on the high speed motor line shows 20-22amps (running full load is rated at 9.5 amps). When the motor terminals are disconnected from the board, the terminals for the motor show 117volts as they should when the system thinks the motor is on.
We have replaced the blower motor with a brand new unit as well as a brand new matching capacitor. The capacitor test setting of the clamp meter indicates the capacitor is good (reading 15.2mfd on a 15mfd rated cap). We have also tried replacing the contactor relay in case that was the source of the noise. No difference.
I'm absolutely stumped. Is it possible the brand new motor is also bad or am I missing something obvious (or perhaps less obvious).