For any newcomer to HVAC systems, installing or troubleshooting a thermostat can be very daunting — and understanding the color codes of thermostat wiring is just another problem. Or, with help from above and following the correct project structure, it can be made easier. Wiring serves a definite industry, each irk is devoted to a certain piece of equipment and its color allows us to pay attention to what we lay and simplify archiving error injury. Here is our guide to the standard thermostat wire color codes, their functions and how you should use them in your wiring process along with a few common HVAC set up tips.
Thermostat Wiring Explained:
But before that (color codes), we will highlight the functionality provided by thermostat wiring. Your thermostat is the command center of your HVAC unit, dictating heating and cooling, and often the fan function as well…and going a bit beyond is humidity and air quality. The thermostat then communicates with the HVAC system with low-voltage wiring that tells it when to heat, cool or turn off.
Most thermostats use 24v wiring lines for communicating with the HVAC system. They are typically: Since different manufacturers sometimes have unique wire-color labels, and each model of HVAC system will have unique wires that may not be included in this general color code. If nothing else, understanding this wiring will at least save you time and frustration when installing a new thermostat or tracking down an issue.
Types of Thermostat Systems:
Single-Stage Systems:
These systems perform just one cooling or heating process, according to the season. Wiring on them is simple as in their chain or few wires.
Multistage Systems:
Similar to the 2-stage system in that there are two stages of heating or cooling, however multistage systems require additional wires to control additional functions.
For Heat Pump Systems :
Since heat pumps use one system for heating and another for cooling, which means that you will need more wires to install than the standard HVAC integration.
Thermostat Wire Color Codes Standard:
So, without further ado let us explain the basic guidelines of thermostat wire color codes that are adhered to mostly in a standardized way making it easy for one to identify. What does each color generally signify?
Red Wire (R):
This is the power wire for the 24 volt transformer which allows power to be supplied to the thermostat.
Variations:
There are two red wires: two different species of the red wire ii. red wire x 2
Rc (cooling power):
This wire only for systems with separate transformers for heating and cooling allow the Rc wire to power the cooling system.
Rh (Heating Power):
This is the wire that powers up the heating system — if you have separate transformers for cooling and heating then Rh goes to the power supply of your furnace.
Note: If your system uses one transformer for heating and cooling, then the Rc and Rh terminals are jumpered.
Yellow Wire (Y):
Yellow:
The yellow wire is tied to the compressor that will engage and disengage the cooling equipment
Function:
It tells the air conditioning to come on.
Y2 (Multistage Cooling) – In some multistage cooling systems, you may also have a Y2 wire, which controls the second stage of cooling.
Green Wire (G):
Function:
Green wire activates the fan in the HVAC system.
Purpose:
The green wire is common to the fan as a go signal between the thermostat and the central unit when changing from heating to cooling.
White Wire (W):
The purpose of the white wire is for the heating system.
Function:
When the thermostat calls for heat the white wire tells the furnace to turn on.
Differences:
If you have a two-stage system, the other stages of heating on it are controlled by W2.
Common (C) or Black or Blue Wire:
Purpose:
The common wire, a blue or black wire also known as the C-wire is used to close the electric circuit.
Result:
It provides a continuous signal to the thermostat which is vital for smart thermostats that require 24/7 power energy for tasks like Wi-Fi.
A few systems do not have a C-wire but this is becoming more common, especially with newer thermostats.
Orange Wire (O/B):
Reversing Valve (Heat Pump Systems Only) – Orange Wire
Purpose:
Its purpose is to change the system from cooling mode and heating mode.
Note: Some systems use the O wire for cooling and the B wire for heating, while some of them are combined as one wire.
Auxiliary Heating Wire (AUX):
Objective:
The auxiliary heating wire stops the backup heat source in a heat pump system.
Purpose:
To supplement the heat pump on really cold days when it can’t efficiently provide enough heat.
Brown Wire (E):
Brown Wire Purpose Heat Pump Systems the emergency heat.
Purpose:
Emergency Heat is for use when your primary heating system fails and becomes a backup heat source.
Blue/Black Wire (Y2):
Application:
These wires are implemented to 2-cooling-stage systems.
Function:
Y2 is the second stage for homes that require additional cooling power in warm climates.
Identifying Thermostat Wires in Your Home:
Keep in mind that the color of your thermostat wiring may not match these standard wire colors, so you ‘ll need to determine how your wires should be designated. Make sure to consult with your wiring manual for additional information corresponding to your thermostat model and HVAC system!
To find the correct wire, complete the following steps:
Disconnect the Power:
Always turn off the power to your thermostat before working on it. After you’ve turned off the power, verify that there is no electricity by using a voltage tester to test your HVAC system at the circuit breaker.
Take off the Cover of the Thermostat:
Using gentle hands, pull off the thermostat cover to reveal the wiring on top.
If you are replacing an old thermostat with a new one, take the time to label each of the wires (on both before and after jumper wire installation), using tape. This will facilitate easier reassembly later.
Check the Manual:
If the colors do not correspond to one of the standard codes listed above, or you are not sure what they mean, consult your HVAC system manual. If needed, check some of the wires using a multimeter.
Thermostat Wiring Troubleshooting:
One minor example: basic color coding still has problems. Common problems types and how you will trouble this.
Faulty Wiring:
If the thermostat is not functioning properly double-check the wiring. Step 7: Attach The Wires To The Correct Terminals Many times all you need is to cross-reference a color with the terminal designation (ie, Red to R, Green to G) and your problem is solved!
Smart thermostats need a common wire, often called a c-wire, to be powered all the time. Similarly, conventional units are typically battery-powered. This will also lead to no power so the thermostat will not work as intended. So what if you do not have a C-wire, possibly needing an adapter or even outside help to install one.
Blank Thermostat Display:
No power Verify Connection of Red Wire (R) For a system that uses both Rc and Rh, verify that the wires are properly connected or that the jumper is installed.
Smart Thermostats And Their C-Wire Requirements:
Smart thermostats like the ones from Nest, Ecobee, or Honeywell often require that you have extra wires, usually a C wire. For what it is worth, these thermostats are powered all the time to run features like Wi-Fi and remote sensors(disposing 2 AA batteries per year). Most dated HVAC systems may not route through a C-wire, for which the homeowner might need to install one or opt for a C-wire adapter with these newer thermostats.
Some hacks to work around a no-C-wire issue if you are upgrading your thermostat to a “smart” version include:
The C-Wire Adapter:
There are typically at least a few smart thermostat makers who make a C-wire adapter that provides a common wire to one of their compatible thermostats as an easy add-on device, saving you the trouble and expenses of hiring someone to run new wires for you.
Professional Installation:
Another alternative would be to hire a professional to install a C-wire to your HVAC system directly, yet this is only necessary if the other options are not viable and more costly. Nonetheless, this guarantees that everything runs appropriately and no future issues happen.
G-Wire:
Alternatively, you can reuse the green (G) wire as your C-wire in some systems. Although at the expense of “stand alone” use of fans, this could provide a fast fix in older systems.
Conclusion:
If you work on an HVAC system, it is important to know the thermostat wire color codes. Though the wiring may seem confusing and complex, once you know what each color is used for and how everything should function, you will be that much closer to diagnosis when there is a problem. The particular need for a previous transformer to use a smart thermostat is often high, however, and this kind of project really demonstrates the importance that correct wiring connections — and then especially one for a C-wire — can serve in maintaining an HVAC being reliable.
