If you are looking for a better understanding of heat pump thermostat wiring, here is an example of a typical electronic type heat pump control wiring that is located inside your house.

There are many types of electronic thermostats in the market these days, hence please check that the type of thermostat that you are using can be replaced with newer ones. A new programmable heat pump thermostat can be purchased for less than $50.

Normally, an electronic thermostat in the United States is powered by a 24V AC power supply which comes from a 110V/24V power transformer. If you are not sure, always refer to the operating manual of your thermostat in your house before attempting to do any troubleshooting or replacement work. As always, if you are not trained to handle electrical equipment, please get a qualified technician to do it.

It is always a good idea to take a picture of the current heat pump thermostat wiring before you start removing them.

In the heat pump system, there are at least 8 wires that need to be connected to the thermostat for proper operation. Watch this video from AC Service Tech LLC for a quick overview of each color-coded wire:


Overview of Different Heat Pump Terminals

As shown in the diagram, you will need to power up the thermostat, and the 24V AC power is connected to the R and C terminals. The color of wire R is usually RED and C is BLACK. C is known as the common terminal. These two connections will ensure that there is power to the thermostat that you are operating. 

The Y terminal is where the signal to the cooling air conditioner signal is connected. This terminal will call for the need to cool the room when the set temperature is lower than the room temperature. The G terminal is connected to the indoor fan which circulates the air in the room.

The reversing valve is a device that reverses the flow of the refrigerant in the piping system. In most cases, the reversing valve is energized when running cool mode. However, there are instances where the reversing valve is off when running cool mode.

Therefore, it is important the check the manufacturer’s specifications of the heat pump system that you are using before you can make a proper connection to the thermostat.

The O terminal is used when the system that you are using has a reversing valve (or four-way valve) which is turned on when running cooling mode. If the reversing valve is turned on when running heat mode, you will need to connect the reversing valve to the B terminal. Only one connection is active at any one time, that is either O or B terminal is used but not both.

In some equipment, there is a 2nd stage of cooling that helps to increase the cooling capacity of the room. In this case, the terminal Y2 is usually used. The color of the wire varies. 

Sometimes, there is a 2nd stage of heating where additional heating is provided to supplement the primary heating system. This is usually installed in regions where extreme winter occurs. In this case, the terminal W2 will be present.

Related: What Does Hold Mean on a Thermostat?

Today’s Homeowner Tips

Some thermostats may have a feature called Emergency Heat, where when set, it will shut off the heat pump. It will then turn on the strip heat which becomes the primary source of heating. This feature should only be used for a while as the energy cost is usually higher than a heat pump system. The terminal used is E.


Features To Look For in Heat Pump Thermostats

Look out for the following features that are incorporated in most modern programmable heat pump thermostats.

  • Low voltage checking prompts you that the incoming power is low.
  • Error codes that tell you the reason why your system is not running properly.
  • 3-minutes minimum compressor off time to prevent the short cycling of the compressor. Short cycling of the compressor will shorten its lifetime.
  • Programmable day and night settings of the set temperature.
  • Weekend settings and setback functions for vacations.
  • Ability to check the status of the thermostat and control the settings remotely via smartphones or computers. The presence of this feature will raise the cost of the thermostat.
Editorial Contributors
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Alora Bopray

Staff Writer

Alora Bopray is a digital content producer for the home warranty, HVAC, and plumbing categories at Today's Homeowner. She earned her bachelor's degree in psychology from the University of St. Scholastica and her master's degree from the University of Denver. Before becoming a writer for Today's Homeowner, Alora wrote as a freelance writer for dozens of home improvement clients and informed homeowners about the solar industry as a writer for EcoWatch. When she's not writing, Alora can be found planning her next DIY home improvement project or plotting her next novel.

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Roxanne Downer

Editor

Roxanne Downer is a commerce editor at Today’s Homeowner, where she tackles everything from foundation repair to solar panel installation. She brings more than 15 years of writing and editing experience to bear in her meticulous approach to ensuring accurate, up-to-date, and engaging content. She’s previously edited for outlets including MSN, Architectural Digest, and Better Homes & Gardens. An alumna of the University of Pennsylvania, Roxanne is now an Oklahoma homeowner, DIY enthusiast, and the proud parent of a playful pug.

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