Hi Bob,

The only thing I can think of is the unloader (if your compressor has
one).
If it's sticking, there may be too much back pressure, and the motor isn't
powerful enough to overcome it.

Don't think that's the case. When I removed the compressor/motor unit from
the rest of the compressor it also removed it from all the air tanks etc.
Like I said, spinning the compressor by hand was very easy. Its just that
the motor won't start on its own.

Thanks,
Mike