I was called out to a moble home that the blower motor stopped running. I went to the force air furnace unit and jumper it to start the blower motor and it started to hum. So I check the Run Capacitor and it was good. So I took of the Blower assembly out and took it to the shop. I wired it up to check it and it worked great in all speeds. So I brought it back and hooked it up and it did the same thing....Hum. Thought it might be the fan relay so i by passed it and it did the same thing. Then I wired it up again to plug it in to a wall plug other then the dedicated circuit for the Air Handler the same thing happen. Then I went to the Moble home next door and plug it in there and it ran fine. The outside 220v compressor works fine so I know there is no problem there. I check all the connections in the panel box to make sure they are tight and they were. Could it be a bad neutral coming from the utility company to when I switch the blower motor on it drops out just enough to make it not start? The strange thing is why it works everywhere but in the home.