On Wed, 29 Jul 2015 08:12:51 -0700 (PDT), Deane Williams
wrote:



Hard to see where a SS AC Relay could hurt an induction motor if the
motor isn't overheating.

Does the fan still spin? Is there continuity in the winding?

John :-#)#

The motor still spins easily. There is no DC continuity from the power plug but I beleive this is normal for induction motors? Perhaps the overheat sensor has opened permenently. Home Depot gave me a replacement so I will try it again. These fans typically last for many years when plugged directly into a wall socket. This is a real mystery to me. Perhaps SS relays generate some large spikes on their output? I should check it with a scope.
Thanks for the comments.

You have an interesting problem. I hope you figure it out. I have
never used SS relays, but I can't image they cause spikes and other
anomolies that would kill a simple AC motor. Is the relay rated for
inductive loads?

By the way, I have a similar fan I purchased years ago. I just
measured its DC resistance and found it to be about 18 ohms on its
high setting. Clearly, that number is no indication of its impedance
at 60 Hz while in operation, but it definitely conducts DC. My best
guess is something is causing the motor windings to overheat and
eventually open. Unfortunately, I can't think of any way to explain
why that would happen.

Pat