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PerryupNorth 11-30-2011 11:52 AM

wiring for two speed Emerson motor
I have a Surefire 101ce wood/electric furnace that I am currently using exclusively as a forced air electric furnace. It has been functioning perfectly except that the motor would occasionally jump around at startup and the problem was found to be the centrifugal startup switch being loose on the shaft, and it was replaced. However after replacement something is wrong and the motor fails to go into the high speed mode or start up in the high speed mode unless it has no load.
A new motor has been ordered, however I have been told that the wires for the high and low speed windings (both 115V) must not be energized at the same time, yet the schematic for the furnace seems to indicate that this is the case (and the old motor operated happily for 29 years).
The old motor is an Emerson SA55JXFGS-4781 cat. 5793
Can this motor have both windings powered at once for the high speed mode? Does this mean it has internal circuitry to automatically cut off the power to the low speed windings in this case?
Would a replacement motor be okay as a direct replacement, or am I going to have to add additional control relays to the two element sequencers which also turn on the low and then high speed fan motor modes to prevent both windings being energized at once in high speed mode?
Thanks for any information or advice on this motor and furnace problem.

Billy_Bob 11-30-2011 01:11 PM

If the new motor is not an exact replacement for the old motor, then try to find technical information about the new motor or call the manufacturer of the new motor and ask.

If you can't get that information nor can call the manufacturer (made in China), then I would go with what the person told you and redesign your system. (As these motors are not cheap!)

PerryupNorth 12-02-2011 10:44 AM

new motor has diagram and works
Thanks Billy_Bob for the advice.
The new motor just arrived and to my surprise had an alternate wiring diagram written on it which showed both high and low speed inputs being energized at once, and the motor was supposed to be an exact replacement. With that reassurance I tried it out, and it seems to work quite nicely. I couldn't get hold of an internal wiring diagram as I am curious how they have set this up, but at least I don't have to wire in an extra relay and breaker.

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