trane xe90 blower
 

OK strange but true, when my xe90 turns on all vent blower and ignition functions work fine. I hear the fan relay kick on for the squirrel cage but the NEW motor hums and wont turn until I give it a spin. Then all is well until it goes through the cycle again. The blower fan just won't start on it's own.

You need to tell me how many wires are coming out of the motor and where they go. It sounds like the motor has a bad capacitor or it is not wired right.
When the motor was installed did they put a new capacitor to match the new motor? Either on the box or on the motor it will tell what capacitor you need.
Later Paul