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Furnace Fan and Limit Controllers

wws Member Posts: 1
Can anyone tells me if the jumper tap has been removed from the Furnace Fan and Limit Controllers unit as the new unit I bought has a brass jumper and has not been remove, I like to match my old unit. Thanks everyone newbie.


  • ratio
    ratio Member Posts: 2,821
    The jumper allows the two functions of the control to be electrically isolated. Use a multimeter on the continuity or ohms range to check between the two terminals of the old control. Continuity/low resistance indicates the jumper is installed, no continuity/infinite resistance indicates it's removed.
  • Tim McElwain
    Tim McElwain Member Posts: 4,474
    The jumper is in place as I can see it in the photo. What that means is the 120 volts feed to the fan side will also be on the limit side. That can be a problem if the limit side is wired through the secondary (24 volt side). In that case the jumper should be removed.
  • ratio
    ratio Member Posts: 2,821
    Were there three wires on the old control, or four?