Here are common uses for wire colors:

  • Blue or Black – C – Common wire, may be unused by your existing thermostat. …
  • Red – R – 24VAC power from the furnace’s transformer.
  • Red – Rc – 24VAC (dedicated to heat call)
  • Red – Rc – 24VAC (dedicated to cooling call)
  • Green – G – Fan.
  • White – W – Heat.
  • Yellow – Y – Air conditioner.

How do I know which wire is C wire?

Quote from the video:
Quote from Youtube video: So it's fairly simple to tell if you have a/c wire or not firstly the purpose of a/c wire is basically for the newer thermostats. As either has a backlit display or has Wi-Fi functionality.

What color wire is the C wire?





Blue wires

Blue wires are also called “C” wires because they are the Common wire. C wires are necessary for any “smart” thermostat that needs to be connected to a power source 24/7, regardless of your heat pump type.

How do I know if I have a blue wire or C wire?

Take your existing thermostat off the wall — it’s usually easy to do — and turn it over. You’ll see wires of many colors, and one of those might be blue. If so, look at the terminal to which it’s attached, and you should see the letter C. The blue wire, or C-wire, is known as the common wire.

How do I know if my C wire is connected to my furnace?

Quote from the video:
Quote from Youtube video: Okay. So now that we've climbed up here we got a nice close-up looky. Here here's the whole furnace unit. And. So what we're gonna do is to find our C wire since we know we have one present always

Can the C wire be brown?





The C, or common wire, provides smart thermostats with continual power. It’s usually blue, but it may also be black, brown or purple. The O or orange wire connects to your heat pump (if applicable).

Does C wire have voltage?

The C wire, a.k.a. the “common wire”, allows a constant flow of 24 VAC (volts AC) power to a smart thermostat. However, the C wire doesn’t provide the actual source of power to the thermostat. The wires that provide the source of power are the R wires (or hot wires).

What if there is no C wire for thermostat?

You most likely have a line voltage system and none of the popular smart thermostats on the market are available to you as-is. (There is some hope with an adapter, but don’t get too excited yet.) This wiring indicates a line voltage system, and you’ll need an adapter or a smart thermostat designed for line voltage.

How do I bypass the C wire on my thermostat?

Quote from the video:
Quote from Youtube video: Add a jumper wire between the Y and G. Terminals. If there's already wires attached just leave them be go ahead and push all the wires in. And close the backplate.

Does Nest work without C wire?



In a system with a C-wire, the Nest charges itself from the C-wire’s current and all is fine. In a system without a C-wire, though, Nest recharges its battery when the heating or cooling runs.

Can I use G wire for C wire?

Option #3: Use a G-Wire as a C-Wire



If there is no hidden C-wire, you can use a G-wire instead. However, you will not be able to use your fan independently when the heating or cooling isn’t running. Also, many HVAC systems are incompatible with this solution, including: HVAC systems using electric heat.

Do I use RH or RC on Nest thermostat?

The Nest Thermostat E only has an R connector, which is typically where an R wire would go. If you have separate heating and air conditioning systems, you might have separate Rh and Rc wires that come out of the wall and are connected to your system.

What is a C wire?



What is a C-Wire? A common wire (C-Wire) provides Wi-Fi thermostats continuous power by connecting it to a heating and cooling system (e.g. furnace). C-Wires are required on most Honeywell Wi-Fi thermostats, with the exception of the Smart Round Thermostat (formerly known as the Lyric Round).

Where is the C wire on an old furnace?

Quote from the video:
Quote from Youtube video: The wire coming from outside from the condenser unit is only going to have two wires a red and a white looking like this. And those two are going to go to y. And c common on that terminal strip.

Why do you need C wire for thermostat?

The C wire, or “common wire” enables the continuous flow of 24 VAC power to the thermostat. Technically speaking, power flows from the R (red) wire, but not continuously (not on its own, anyway). To make it continuous requires a common wire to complete the circuit.

Can I use ecobee without C wire?

If you’re lacking a C wire and have at least four wires at your thermostat to work with (refer to this article if you only have two wires), you’ll want to install the Power Extender Kit (PEK).

Can ecobee be installed with 3 wires?



If you have a heat-only system, you may notice that your thermostat has three wires—R, G, and W. In this scenario, the Power Extender Kit (PEK) is not compatible. There are three options available to create a C wire and make the ecobee compatible.

Can I install a WIFI thermostat with only 2 wires?

The Nest Thermostat is not only the best 2 wire wifi thermostat but it is one of the best wifi thermostats you can get for your home. The Nest Generation 3 thermostat can be used with heating only and cooling only systems and requires only wires.