Issue is blower motor stays on. Even with AC/Off/Heat set to Off, blower motor stays on, regardless of Auto/Fan setting. Only way to turn off Blower motor is to turn off circuit breaker to the unit.

Heater & AC both work fine.

Inside Fan Motor Relay clicks, so is expected that it is okay.

* There is a delay timer circuit board attached to the relay. Not sure how to test this. I'd expect that the failure mode of a timer board is "always off" -- instead of the "always on" that we are experiencing.

* Attached inline to the timer board is what appears to be a thermodisk in the heat strip plenum area.

Questions as to why the blower motor stays on:
1) Is it reasonable to expect that the timer board would fail "off" or could this be the cause?
2) It is reasonable to expect that a thermodisk could fail in such a way that the unit believes it is over temperature, and that the disk is telling the ciruit to turn the blower on to save the house from catching fire?
3) How is the thermo disk tested? First check was with ohm meter, it showed open circuit at ambient temperature.
4) If it is a thermo disk failure, what temperature thermo disk should be used?

Thanks!
--Mark