4 wire thermostat wiring blue red green white diagram base

Even the most seasoned people who enjoy DIY may come across problems with wiring a thermostat. I will explain that in a little more detail further down this page. What I would like you to know is the information detailed below is based on the industry standard, yet not all thermostats will work this way simply because letters and numbers are used as well as color. So, this is what you might expect to see in terms of colored wires and what they mean:.

AND it has been recorded by a professional in the industry. Thermostat Center is supported by our readers. When you purchase an item through links on our site, we may earn an affiliate commission. Wiring Set-Up Explained What I would like you to know is the information detailed below is based on the industry standard, yet not all thermostats will work this way simply because letters and numbers are used as well as color.

So, this is what you might expect to see in terms of colored wires and what they mean: White — The white wire is what connects to the auxiliary heat on your system. Yellow — The yellow wire connects to your compressor.

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Green — The green wire connects to the fan. Orange — This wire connects to your heat pump if you have one. Red — Now, there can be two separate wires for this.Problem is that I have a red, a white, a green and a blue wire. The three wires are red, white, and blue or yellow, depending on the manufacturer. The main difference setting each apart is the number of colored wires.

4 wire thermostat wiring blue red green white diagram base

The red wire is the source hot wire from the transformer. This wire pair is simply a wire splitter, where a blue wire is splitted into yellow and green wires. HVAC systems with more functions need more wires to communicate to and from the thermostat. The red wire was connected to "Rc" terminal, green to the "G" terminal, white to the "W" terminal, and blue to the "Y" terminal. When I hooked up the Nest I just left the blue wire unconnected.

The Southwire ft. First oder of business was to replace old round thermostat with new digital. This diagram is to be used as reference for the low voltage control wiring of your heating and AC system. Or Red to the thermostat R terminal which is shared with both the heating and cooling.

It has a 'Replace Batteries' indicator that says 'Replace batteries' right there on the display. The diagram below shows how a basic 4-wire thermostat is connected as indicated by the color code chart above. I've detached my old thermostat, and I'm trying to figure out how to match up the wires.

It is made for simple heating systems which is the most common system in homes.

Thermostat C Wire: Everything you need to know about the “common” wire

You'll need to check your current thermostat's wires to tell if your system is Nest thermostat compatible and to help with Nest thermostat installation. Ye olde thermostat. But there is no particular standard for thermostat wires, so it can be any color like Yellow, Brown, Green or any other color.

Red C. Blue wires are for heat pumps, like orange wires. I have a question about the blue wire running from my air conditioning unit to my thermostat.


Push excess wire into wall and plug hole with a fire resistant material such as fiberglass insulation to prevent Mountingdrafts from affecting thermostat operation. I have all wires identified, except I have a blue wire at the thermostat that only conects to a blue wire going to the compressor.

Older thermostats usually don't have a C-wire because they either don't need power or, if they do, they get it from a battery. Keep the following list handy whenever you decide to peak behind your thermostat. To find out if your system has a C-wire Other models, like the Nest Learning Thermostat and the Honeywell Lyric can use a C wire, but they don't require it. C, 24 volts AC.

So I did the same with the new thermostat. Where does it go?

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Contractor's Assistant: Just to clarify, do you think this is a larger HVAC problem, or something specific to the thermostat? I am not sure. The common wire is usually blue or black, but that is not guaranteed. If the blue wire is connected to the Y terminal then connect the Blue wire to the Y terminal in the new thermostat.

Always refer to your thermostat or equipment installation guides to verify proper wiring.

Interpreting Thermostat Wire Colors

Yellow, Brown, Orange, Black. Expected a 5 wire system. The basic thermostat is a 2-wire thermostat and its main disadvantage is that it is used only for heating.

It's there so you can supply power to the heating and cooling switches with a single wire, which is usually red.While there isn't an official standard for thermostat circuit wiring colors, there is a general pattern. Your best bet is to see the manufacturer's documentation both thermostat and HVAC. If there is a short then the current through the tiny wires could cause a fire Thermostat wires are usually 18 gauge.

These colors are not standard for thermostats. If you need an inexpensive meter to work with thermostat wiring see M We also have meters that can display thermocouple temperature Process Control Meters.

The thermostat is a set of contacts where G, W and Y are connected to R based on the following rules. If there is a call for cool, R is connected to Y compressor. In air conditioning mode the thermostat controls the fan, so G Fan is also connected to R.

For cooling, the furnace usually selects the high speed of the blower. In conventional heating which is oil or gas, the furnace controls the fan, so only R is connected to W heat.

For heating applications, a lower blower speed is used and the furnace selects it. The furnace controls the fan because oil and gas heat is not instantaneous. In order to avoid a blast of cold air, the furnace controls the fan. It can do this with a simple delay or by temperature set by the limit switch in the plenum. Rc and Rh have been added to accommodate separate transformers for cooling and heating, respectively.

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Thus, for single transformer systems, Rc and Rh are jumpered together and assume the function of the R terminal. Some systems use R and Rc; so consider R to be Rh in this case. Rc is defined as R cooling and Rh is defined as R heating. Often, both letters are in uppercase as in RC and RH. To run the fan, the thermostat connects the Fan G terminal to R.

4 wire thermostat wiring blue red green white diagram base

The Common C terminal has been a recent addition because modern electronic thermostats need power to operate. Early thermostats did not require power because they used either mechanical snap-action switches or switches containing the liquid metal mercury. Mercury is a hazardous material and must be disposed of properly.

4 wire thermostat wiring blue red green white diagram base

The current available is limited by the resistance of the furnace relays and may not be sufficient to run some thermostats e. Some electronic thermostats are powered by a set of batteries. In this case no C terminal is required, but when the batteries die you have no air conditioning or heating.

Programmable thermostats require a way to know the time and it needs to know the time during power outages. A thermostat may contain a small lithium battery just as your laptop or PC does.

The battery may be rechargeable or it can be implemented using a supercap or Super capacitor. These are very high value capacitors which can run the clock for maybe a day or so. Your setpoints in an electronic thermostat are not susceptible to being lost when the power fails because they are stored using a different technology. The technology is continually evolving, but the lifetime may be 10 years or more with say 15, write cycles.

In many heating systems especially those with heavy radiatorsthere is a great deal of "stored heat" in the system once it's hot, so the inside temperature will continue to rise for some time after the system turns off.

If the thermostat were to wait until the desired temperature were reached before shutting off the system, that stored heat would continue to heat the building, overshooting the desired temperature by several degrees. To prevent this, old mercury thermostats used to pass a specific current through the bi-metallic spring to artificially raise its temperature, so the heat cuts off sooner.Typical 4 wire thermostat t-stat wiring examples follow.

Some have the common C wire, while others do not. Both examples of how to wire a Honeywell thermostat with 4 wires are discussed below. Of course though, you should check that the wires in your HVAC system match up with their expected functions. The red wire R, RC, RH connects the high side of the output of the control transformer to the t-stat. Also referred to as the C wire, this wire connects the low side of the output of the low voltage power to the t-stat.

Note that in our case, we had to use the green wire for C, as discussed below, because there were only four wires coming from the furnace to the t-stat which included no blue, brown, or black wire.

So we decided that we could do without the fan switching function that the G wire normally provides, in favor of the remotely programmable capabilities of a Wi-Fi smart t-stat that must have a C wire in order to function. Later on though, we hope to run new t-stat wire, that has more conductors, so we can get the C as well as the G wires. This wire controls the cooling first stage.

The t-stat connects this lead to the R wire when it calls for the cooling system to come on.

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This involved getting into the furnace at the other end of the wires, and moving the green wire from the G to the C spot on the wiring block. In this case, we chose to give up control of the fan, to power our Honeywell Wi-Fi t-stat. The next t-statthe Honeywell T87N big dial model, needs no common wire.

Again, no blue wire here. This t-stat also needs no C wire. For this one, the red wire would attach to the R screw, the green to the G, the yellow to the Y, and the white wire to the W terminal, for single stage operation of both heating and cooling systems.

Skip to content. Like this: Like LoadingHow to wire a thermostat. To wire a thermostat, you must first be aware of the type of system that you have in your home. The thermostat wiring on these systems can have very similar wiring properties. But what if you have a system that's a little different like a Heat Pump System, Then your thermostat is going to be wired a little different as well.

First and foremost when you go to wire a thermostat, if you have any doubt of the type of HVAC system you have and are uncomfortable with wiring, then I highly recommend using a qualified HVAC service technician to complete your task. This could save you a lot of unnecessary expenses in the long run. Now the thermostat circuits I will be covering will consist of the two scenarios I mentioned above.

But an important issue here is that the diagrams and wiring color codes are going to be the most common standardize method. Always keep in mind that who ever wired your thermostat may not have followed these procedures and your color codes will not match the following examples. You will have to determine this before you start disconnecting any of your thermostat wiring.

I would highly recommend that you write down what color wire is going to which terminal. This way if your color codes don't match the normal code as the chart below indicates, you can still get a good idea of which wire should go where on your new thermostat. If you're changing your old style thermostat to a programmable type, then most HVAC systems are compatible and will work just fine with a programmable unit.

But in the case of a Heat Pump system, You'll really have to do some research to verify that the programmable thermostat will work. The following is a chart showing the most common terminals and their respective color codes and what that particular wire is used for in the circuit.

Now most thermostat's will not have all of these termination points but the chart will help you determine color code and connection points for your particular unit. The diagram below shows how a basic 4-wire thermostat is connected as indicated by the color code chart above. The diagram shows how the wiring works. However your connections may seem a little different on the thermostat itself. Just take a look at the picture below the diagram.

Some thermostat units have a dedicated R terminal and it jumpers to the RC, RH or 4 terminals internally. The W, Y and G terminals should be pretty straight forward on most all types of thermostat's. The following image is one of the most popular scenarios today. This type thermostat is relatively easy to connect or change over to a programmable type thermostat.

As mentioned in the previous paragraph, the only difference might be the lack of an "R" connection. Now the following image here represents a heat pump system thermostat. These types systems are more involved because of the components associated with the system. Color codes may be different from one household to another, but generally the concept should be the same. It's going to take a little research on the owners part to declare what is involved with your heat pump system and verify proper color codes.

If you're changing a heat pump system thermostat to a programmable thermostat, be sure that the new thermostat is compatible with your style of system.

Once that is verified, the owners manual should be informative enough to complete the change over very easy. Be sure to check out my Thermostat Store for great bargains on all types of thermostats. I know it for it a fact.

Watch this video for assistance on upgrading or installing a programmable thermostat. Here's How. How To Wire It.Login or Sign Up.

Logging in Remember me. Log in. Forgot password or user name? Posts Latest Activity. Page of 1. Filtered by:. Previous template Next. I just purchased the wired version of the Insteon Thermostat and have an installation question.

My existing wiring is only four wires: green, red, blue and white. I attached a picture of the current wiring and am confused about how to wire existing wires to the new Insteon thermostat.

If that is required, please let me know and how to wire it. RC and RH seem to have more juice. Does that mean I have a C Wire? Thanks in advance. Last edited by hamada ;AM. Tags: None. You do not have a C wire.

What you need is an Add-a-Wire Kit. Message from Forum Admin: stusviews passed away in April Stu was a huge fan of Insteon and a huge presence on both the Smarthome and Insteon forums, helping thousands of us along the way he had nearly 20, posts to his name. We thank him for his contributions, dedication, and passion for making the Smart Home a reality.

Thermostat signals and color code

He will truly be missed. Saving energy is not always free.

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Be a world saver. Comment Post Cancel. Originally posted by stusviews View Post. Yes No. OK Cancel.Smart thermostats often require a continuous flow of power to maintain their displays and network connectivity. They usually need a common wire or C-wire to provide this continuous power. Power flows from the red wire, but not continuously so the common wire is necessary to complete the process. When everything is complete, the thermostat will have a continuous supply of volt energy.

The common wire is usually blue or black, but that is not guaranteed. The previous homeowner may have made the wires whatever color they wanted or they could have run any wire they had available, so never rely on color alone. Regardless of color, the common wire is connected to the C port inside your thermostat. If you are unsure, it is always best to consult with an electrician or HVAC expert. A C-wire is required for many smart thermostats because they need a constant flow of electricity from the furnace in order to keep the smart components running.

Smart thermostats usually have Wi-Fi in them so they can communicate to the internet, which allows you to monitor or change the temperature when you are away. In addition, smart thermostats also have a lit color display, which uses power. Unfortunately, batteries will not provide enough power for a long enough period of time to be useful, thus the need for the C-wire power from the furnace or boiler.

Not all smart thermostats require a C-wire. Some of the newer models include circuitry that captures the intermittent power from the red wire to charge an internal battery.

This means they can run entirely without a common wire, which makes installation a lot easier. For instance, the Nest Thermostat and the Nest E Thermostat can usually run without a common wire — see below for more information.

4 wire thermostat wiring blue red green white diagram base

Other thermostats, like the Ecobee, come with an adapter that can be used if you already have four wires, but no common wire — Ecobee thermostats are also discussed below. The best way to figure out if you need to adjust to a c-wire system is to take your thermostat off the wall and see what it looks like. If your wiring looks anything like the diagram below, you are okay with any smart thermostat you want.

You have the proper blue c-wire running into the C slot. This wire sends a constant flow of energy to your system and requires no changing. You may want to take a look behind your current thermostat bracket to see if there are any additional wires.

If your home is old or you have an older heating system, then you may not have a common wire. That doesn't mean you can't use a smart thermostat. You have a few options if you want to use a smart thermostat without a C-wire. Yes, the thermostat uses low amperage and low voltage power, but it is still important to turn off power to your HVAC system when running and connecting the wires to prevent injury or damage.

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