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I only have 4 wires is one of them the C wire?

Last Updated: Sep 06, 2014 03:14PM UTC
In most cases no.  If you have a gas, oil or propane heating system and an air conditioner you will not have a c wire in your 2 wire wiring.  So if your wires were labeled R W Y G there is no C wire.  

But there is a way to use your G wire as a C wire.  If you use this option you will loss the capability of operating your fan with the fan on and off switch.  But the fan will still come on with your heat and AC.

To use your G wire as a C wire do the following:
  • Turn off the power to your HVAC system
  • You will need a small piece of 18 gauge wire also know as thermostat wire
  • You will also need a screw dirver
  • Next go to your furnace and remove the cover and locate the control pannel
  • Remove the G wire from the G terminal and put it on the C terminal 
  • Next take the small piece of wire and put it on the G terminal and put the other end on the Y terminal with the Y wire
  • Replace the cover on the furnace
  • Next at the thermostat remove the G wire and put it on the C terminal
  • Turn the power back on.
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