How To Identify A Thermostat Common Wire (C Wire) & What It Does For Smart Thermostats
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- เผยแพร่เมื่อ 7 ก.พ. 2025
- In this video we teach you how to identify a common wire also known as a c wire and what it is for when installing a smart thermostat.
Common Wire Adapter: amzn.to/3ysXAAK
How To Identify A Thermostat Common Wire:
1. Turn off the power to your existing HVAC system
2. Remove the existing thermostat from the wall.
3. Inspect the existing wiring to see if you have a c wire also known as a common wire. If you have a common wire it will be connected in the C wire terminal of your existing thermostat.
It's important to note that even if you don't have an C wire currently wired to your existing thermostat you may still be able to wire up a smart thermostat that requires a C wire. There are several options.
1. Check for extra wires
Check your existing thermsotat wiring for extra wires. Sometimes there is an unused wire in the thermostat bundle that can be used as a C wire and wired up to the new thermostat and it will also need to be wired up to the existing HVAC system control board.
2. Run a new common wire
You can run a new C wire from your thermostat to your HVAC system.
3. Use your G wire as a C wire ( Common Wire)
You can use your G wire which is the independent fan control as a C wire. You just rewire the g Wire to the C terminal on both the thermostat and at the HVAC system control board and then you have a new common wire. The only downside to this method is that you no longer have independent fan control.
4. Install A Common Wire Adapter
You can install a common wire adapter like this: amzn.to/3ysXAAK
This is the only video that answered each of my questions and explained everything so well.
Great to hear! Thanks for watching!
Thank you for the explanation, it took a long time to find out what C actually was.
Thanks!
Best video explaining C-Wire that I've found. Tks.
Very clear explanation. Thanks for sharing
Best explanation I've heard. Thanks!
Super simple to follow thank you
Thanks for being a subscriber! I appreciate the support!
@@OneHourSmartHomewhat happens if I had an old furnace and there isn't a ground wire but my New one needs it is there hey, we need to run a ground wire without going in the Attic or underneath the house
Great video. Outstanding explanation.
This was ridiculously informative, tysm
I had to log in just to like n subscribe, Great explanation, thank you so much!
excellent explanation
this was very informative but I dont have an extra wire so I was going to move G to C, as explained. However, you say change it to C at the HVAC system. I have a split system so are we changing it at the heater, condensor, or both?
Thank you, even somebody as dumb as me understood this. Very helpful!
Perfect explaining 🫡
Great video. I have both the blue and green wire connected to the C on my old iComfort thermostat. Trying to upgrade to the Nest 4th gen thermostat , can I connect green and blue wire to the C slot in the Nest thermostat or do I separate them?
Great explanation, TY
Thanks now I know what the C wire is.
Excellent video in every respect. Only one situation NOT covered. How can a person install a C wire to an OLD SYSTEM NOT HAVING A MAIN MODERN MOTHERBOARD ON THE FURNACE???
exactly, I dislike that for that reason
Great video! I have my green and blue wire connected together in the C on my old iComfort thermostat. I’m upgrading to the Nest 4th gen thermostat, do I keep the blue and green wire connected the C slot or should I separate it? Thanks for any input .
Great video, thanks.
Thank you!
Great video! I have my green and blue wire connected together in the C on my old iComfort thermostat. I’m upgrading to the new Nest 4th gen thermostat, do I keep the blue and green wire connected in the C slot or should I separate it? Thanks for any input . 6:26
Thanks a lot for the great video. I have AC (cold/hot) and there are 3 wires only. The existing thermostat has a digital screen but no back light even. Any suggestion on how can I install a smart thermostat? The AC is a split unit where there is an external unit and ceiling mounted internal unit.
Thank yu for the info
When a disconnected C Wire is found at the thermostat, do you assume it’s connected at the HVAC Unit? Is there a way to determine this at the thermostat?
I vaguely recall.... After moving G wire to C, don't you need a jumper wire between G terminal and Y terminal ?
Hi ,can i used first generation nest with a heat pump sistem??? If so do you have a video explaining how to install
The wires
great video!
I would double like this video if I could
In case if it helps someone, if there's no C terminal on the thermostat, don't attack the blue wire to anything. Tape it and put away.
Is the C wire always blue?
My C wire is black is that okay?
C wire is like finding the G spot. 😂
I'm not a professional, but I wouldn't be comfortable getting rid of my ground for any wiring (even low voltage) running through my walls. That just seems like asking for trouble.
G doesn’t mean ground in this case. There’s no “ground wire” for the thermostat - actually the C wire is closer to the typical function of a ground wire than any of the others (it’s an unloaded negative path).
@@nekkrist He was talking about the common wire. Which is the other side of 24v transformer. Common at the thermostat was not needed in old analog thermostats . They are nothing more than a set of switches switch. Hot and common to a switch goes boom. Fork in the light socket experiment proves this! Then came digital thermostats. Rather have a new wire ran a battery was enough to power the display. Now that we have fancy thermostats with wifi we need power and common or it will not be able to operate
Great video. I have both the blue and green wire connected to the C on my old iComfort thermostat. Trying to upgrade to the Nest 4th gen thermostat , can I connect green and blue wire to the C slot in the Nest thermostat or do I separate them?
Great video! I have my green and blue wire connected together in the C on my old iComfort thermostat. I’m upgrading to the new Nest 4th gen thermostat, do I keep the blue and green wire connected in the C slot or should I separate it? Thanks for any input . 6:26
Great video. I have both the blue and green wire connected to the C on my old iComfort thermostat. Trying to upgrade to the Nest 4th gen thermostat , can I connect green and blue wire to the C slot in the Nest thermostat or do I separate them? Thanks for your input.
Great video! I have my green and blue wire connected together in the C on my old iComfort thermostat. I’m upgrading to the new Nest 4th gen thermostat, do I keep the blue and green wire connected in the C slot or should I separate it? Thanks for any input . 6:26