In a heat pump, which thermostat terminal is typically connected to the reversing valve control?

• A. B
• B. Aux
• C. O
• D. C

Answer: (C)

The reversing valve is driven by a dedicated thermostat output that sends a 24-volt signal to the outdoor valve coil. This output is typically the O terminal (energize in cooling), or the B terminal (energize in heating), or a combined O/B terminal on many thermostats. The C terminal provides the common side of the 24-volt power supply and does not switch the valve. So the valve control is normally connected to O or B, not to the common terminal. Depending on the system, O energizes in cooling and B energizes in heating, with some thermostats using a configurable O/B terminal to cover both behaviors.