Heat Pump Thermostat Wiring Diagram

Hello and welcome to our comprehensive guide on heat pump thermostat wiring diagrams. In this article, we will explore the ins and outs of heat pump thermostat wiring, including its advantages, disadvantages, and alternative options. By the end, you will have a thorough understanding of how to properly wire your heat pump thermostat for optimal functionality and efficiency.

1. Understanding the Basics

Before we dive into the wiring diagram, let’s first understand the basics of a heat pump thermostat. A thermostat is a device that controls the temperature of your heat pump system by turning it on or off, depending on the desired temperature. It acts as a bridge between the heat pump and the HVAC system, ensuring that the desired temperature is maintained.

A heat pump thermostat typically consists of several terminals or wires, each serving a specific function. These terminals include R, C, Y, W, G, O/B, and AUX/E.

2. R Terminal

The R terminal, also known as the power terminal, supplies power to the thermostat. It is usually connected to the 24-volt transformer, which provides the necessary voltage for the thermostat to function.

3. C Terminal

The C terminal, short for common terminal, is used to complete the circuit and provide a return path for the 24-volt power. It is essential for the proper functioning of the thermostat and is typically connected to the common wire of the HVAC system.

4. Y Terminal

The Y terminal is responsible for controlling the cooling function of the heat pump system. It is connected to the compressor of the heat pump and activates it when cooling is required.

5. W Terminal

The W terminal controls the heating function of the heat pump system. When heating is needed, the thermostat sends a signal to the W terminal, which activates the heat pump’s heating elements.

6. G Terminal

The G terminal is used to control the fan of the heat pump system. When the thermostat signals the fan to turn on, it sends a signal to the G terminal, which activates the fan.

7. O/B Terminal

The O/B terminal is responsible for controlling the reversing valve of the heat pump system. It determines whether the heat pump is in cooling or heating mode. For cooling, it sends a signal to the O terminal, and for heating, it sends a signal to the B terminal.

8. AUX/E Terminal

The AUX/E terminal is used for auxiliary or emergency heating. When the temperature drops below a certain set point, the thermostat activates the auxiliary heating elements connected to this terminal.

9. Advantages of Heat Pump Thermostat Wiring Diagram

The use of a heat pump thermostat wiring diagram offers several advantages. Firstly, it allows for easy installation and setup of the thermostat, ensuring that all the wires are correctly connected. Secondly, it provides a visual representation of the wiring, making troubleshooting and repairs more accessible. Lastly, it ensures that the heat pump system operates efficiently, saving energy and reducing utility bills.

10. Disadvantages of Heat Pump Thermostat Wiring Diagram

While heat pump thermostat wiring diagrams have their benefits, they also have a few drawbacks. One of the main disadvantages is the complexity involved in understanding the different terminals and their functions. Additionally, if the wiring is not done correctly, it can lead to system malfunctions or even damage the heat pump system. It is crucial to follow the wiring diagram precisely and seek professional assistance if needed.

Alternative Options

Aside from a traditional heat pump thermostat wiring diagram, there are alternative options available. One popular alternative is a wireless thermostat, which eliminates the need for physical wiring. Instead, it uses wireless technology to communicate with the heat pump system. This option provides flexibility in thermostat placement and reduces the risk of wiring errors.

Terminal Description
R Power terminal, supplies power to the thermostat
C Common terminal, completes the circuit and provides a return path for power
Y Controls cooling function
W Controls heating function
G Controls fan
O/B Controls reversing valve for cooling/heating mode
AUX/E Used for auxiliary/emergency heating


In conclusion, understanding the heat pump thermostat wiring diagram is crucial for the proper installation and operation of your heat pump system. It is essential to familiarize yourself with the different terminals and their functions to ensure a successful wiring process. If you are unsure or uncomfortable with the wiring, it is always best to seek professional assistance. By following the wiring diagram accurately and choosing the right thermostat for your needs, you can enjoy the benefits of a well-functioning and energy-efficient heat pump system.