Makes me wonder too, from what little you said sounds like it should have worked. I know I've hot wired 'regular ac' fans before and they work fine, not sure how it was wired from the microwave though, it very well could have been in series with something else, the question is did you pay attention to what else it was wired with when you took it apart? It may have been because the motor wasn't loaded? That's a bit of a stretch but I'm not sure what else to think of, mind you I'm pretty week on the varied abilities of motors.