We removed both high and low needles, blew through them, no blockage noted. I'm not sure how to determine that the diaphragm flaps. I believe that it takes such a low volume of air that it would be easy to damage the diaphragm if we just blew threw to it. Also, it is under a metal cover, so how can we determine that it's flapping? Thanks so much for taking the time to reply, it is really appreciated.
Ken McCormack