Here are my thoughts regarding your findings:
It's obvious to me that the Yellow phase wire on the motor is the only one out of the three which is working properly, which is why the motor slows when this wire is disconnected.
As the Blue and Green Phase wires are not affecting the speed, it would appear that the problem is common to both of these wires.
As the most obvious thing these two wires have in common is the windings which go directly between them, it would be reasonable to expect that the fault is with these windings.
We already know that the windings are not shorted to ground.
It is highly unlikely that two pairs of windings have broken on a new motor.
I still suspect that the windings between the Blue and Green phase wires are incorrectly connected:
Option 1One of the two windings has been connected in reverse, each cancelling out the magnetic field of the other.
(As indicated in diagram B above)This is the option I would place my bet on.
Option 2Both of the windings have been connected in a reverse direction, giving a reversed magnetic field.
(Similar to the lower winding shown in diagram B above)Option 3Each of the windings has been connected to just one phase wire, and would therefore produce no magnetism at all.
(As indicated in diagram C above)If you had obtained two low and one high resistance reading
(i.e. 0.3, 0.3 and 0.6 ohms) I would have chosen this scenario.
I could be barking up the wrong tree, but I feel sure it's option 1, but I'm not going to rule out option 2 just yet.
Does anyone else have any opinions on these findings?
Alan