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C Wire - how to use an extra wire as a C wire

Last Updated: Jul 15, 2013 04:10PM UTC

Often times there are extra wires in the wall, and you can use one of those wires to power your Thermostat. Follow the directions below:

  • Turn off power to your HVAC unit
  • Find your thermostat terminal block inside of your HVAC unit (you most likely have to remove a protective panel)
  • Connect one of the extra wires to the "C" terminal on your HVAC unit (this likely has a "C" label, and possibly has another wire connected to it)
  • Connect the other end of the same wire to the "C" terminal on the thermostat
  • Replace protective panels on the thermostat and power back on your HVAC
  • Test that the thermostat has power by removing the batteries. If the screen stays on when the batteries have been removed, then you have successfully applied power to the thermostat.
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