The most common thermostat wiring colors are:

Red- This is typically the wire for the 24 volt “hot” side of the transformer
Green or bare copper- This is typically the ground wire
White- This is typically the wire for the “common” terminal of the transformer
Yellow- This is typically the wire for the “cooling” terminal of the transformer

If you have a “heat pump” system then you will also have:

Orange- This is typically the wire for the “emergency heat” or “auxiliary heat” terminal of the transformer
Blue- This is typically the wire for the “reverse” or “changeover” terminal of the transformer. This is used for systems that have both heating and cooling modes.

If you have a “multi-speed” blower then you will also have:

Brown- This is typically the wire for the “low” speed terminal of the blower motor
Black- This is typically the wire for the “high” speed terminal of the blower motor

If you have a “single-stage” heating or cooling system then you will only have the first four thermostat wiring colors. If you have a “heat pump” system then you will also have the orange and blue thermostat wires. If you have a “multi-speed” blower then you will also have the brown and black thermostat wires.

If you are not sure which wires go where it’s best to take a picture of the old thermostat wiring before you remove it or label the wires with tape so you know which wire goes where.

If you are still having trouble, there are many online forums and videos that can help you figure out the correct thermostat wiring for your system.

The thermostat is basically a switch that turns your HVAC system on and off. However, it’s not as simple as just flipping a switch. The thermostat has a lot of different components that work together to make sure your HVAC system is running properly.

The first thing the thermostat does is sense the temperature of the room. It does this with a sensor, usually located on the back of the thermostat. This sensor is what tells the thermostat when to turn the HVAC system on and off.

The second thing the thermostat does is control the fan. The fan is responsible for circulating air in the room. The thermostat will turn the fan on and off as needed to maintain the temperature of the room.

The third thing the thermostat does is control the heating and cooling elements. These are the things that actually heat or cool the air in the room. The thermostat will turn these on and off as needed to maintain the temperature of the room.

The fourth and final thing the thermostat does is keep track of the temperature. This is so it can turn the HVAC system on and off as needed to maintain the desired temperature.

4 Wire Thermostat Wiring Color Code

Most thermostats use a four-wire configuration to connect to the HVAC system. The four wires are used to provide power, ground, and the two control signals needed to operate the furnace or air conditioner. The most common wire colors are red, green, yellow, and white.

The first thing you need to do is determine which type of system you have. If you have a gas furnace, the wire colors will be different than if you have an electric furnace. The most common colors for each are listed below:

Gas Furnace:

Red – 24 VAC power

Green – Fan control

Yellow – Heat control

White – Common

Electric Furnace:

Red – 24 VAC power

Green – Fan control

Yellow – Heat control 1

Heat control 2 (optional)

White – Common

The next thing you need to do is identify which wires go to which terminal on the thermostat. The most common terminals are labeled “R”, “G”, “Y”, and “W”. Once you have determined which wires go to which terminals, you can connect them accordingly.