"Asimov" wrote in message
...

Yes, I think it is there to keep ice from building up on the room
radiator fins. This is Canada after all, and though the days are very
warm in the fall, the nights get cold. I wrote the sensor clips onto
the radiator return line but I was mistaken, it is the pipe that
brings the cold coolant into the room radiator. Sorry for the mixup.

What I still don't know is if the defrost interrupter contact is used
in normal operation or if it is simply a fail-safe device in case of
an abnormal event like the main thermostat getting stuck? It is too
cold to test right now and I don't know if I should go looking for the
part if it isn't really needed.

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It should cut off the compressor but not the fan. That way the fan will help
clear the evaporator ("radiator") and clear the water that condenses from
it. It's OK for it to operate in normal use - high humidity and cool
temperatures for example.

N