What is a changeover valve on a heat pump?

The changeover valve is a device which reverses the flow of refrigerant in the heat pump. This will allow the freon to reverse and heat the home or cool the home. Honeywell uses an O terminal to energize the valve in cooling and a B terminal to energize the valve in heating. Some manufacturers of heat pumps may use the B terminal to energize in heating, while a vast majority energize the O terminal in cooling.