Furnace Blower motor buzzing and will start spin sometimes and not others, only on assist......

In my experience it has been the motor start capacitor that is easily replaced and available at electic supply houses. Hope this helps

Could be a start capacitor, but I'd say that's most likely a failed start winding. If it happens to stop with the failed winding "on deck," then it can't start itself. If it stops on a good winding, it starts fine. It only needs to move a few degrees to get from a bad winding to the neighboring good winding, so the vibrations of walking near it or opening the cabinet can be enough to move it. Which leads to the annoying, "every time I go and check it, it works fine" effect.

At least, that's the most common failure I've seen cause intermittent start problems with motors.

If you have an ammeter, you should be able to find some instructions online for troubleshooting motors, and follow them step-by-step to diagnose the problem.

Joe

Should have mentioned I am not a professional but Joe is, listen to him. good luck

AC motors don't typically use brushes, especially the ones used in HVAC. Is it direct drive or belt drive? Direct drive is usually a PSC motor with an external run capacitor. If they go bad; it will cause these symptoms. A quick test is to disconnect it from the motor and put an ohmmeter on it. You should see what looks like a dead short with the resistance increasing as the capacitor charges. A new one is only about $10-20. If that doesn't solve the problem, you probably need a new motor. Good luck!

Chris