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  1. #1
    Join Date
    Jun 2004
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    I have a perfectly running (knock on wood) Trane THS050 gas furnace that's about 15 years old. On the schematic diagram, there is a limit switch designated as Aux. Limit that's in series with the Main limit and Vent limit. It's inside the blower compartment with the sensor mounted on the wall between the blower compartment and heat exchanger. Its a SPST switch that opens at 160 degrees F and closes at 130 degrees F. What is the safety purpose of this switch? Again, I'm not trying to replace it but am curious as to what disaster could happen if it malfunctioned.

  2. #2
    Join Date
    Mar 2003
    North St Paul MN
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    Usually see them on downflow furnaces. If the blower motor malfunctions, it turns off the burners. (since heat rises.)
    I'd rather have a bottle in front of me, than a frontal lobotomy.

  3. #3
    Join Date
    Jan 2005
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    a secondary limit.If primary limit should fail that limit should open.

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