Which thermostat terminal controls the reversing valve if the manufacturer energizes the reversing valve in heating mode?

The B terminal is responsible for controlling the reversing valve when the manufacturer has designed it to energize in heating mode. In a heat pump system, the reversing valve is a critical component that determines whether the system is in heating or cooling mode.

By energizing the B terminal, the system activates the reversing valve, allowing refrigerant to flow in the appropriate direction for heating. This mode of operation effectively transfers heat energy from outside to inside the building during cold weather. The control logic of many heat pump systems dictates that the B terminal is energized in heating mode to ensure that the reversing valve functions correctly and establishes the necessary heating cycle.

In contrast, the other terminals do not perform this specific function regarding the reversing valve operation in heating mode. Understanding the roles of the thermostat terminals in this context is essential for the proper diagnosis and servicing of heating and cooling systems.