Notice: Disregard the arrow direction on the valve body.
Heat Pump Operation (Default)
Port B opens to Port A. Fluid flows through the tee to the water in fitting feeding the unit heat exchanger.
Waterside economizer operation (24V applied to the actuator open @ the black and white actuator leads)
Port B opens to port AB. Fluid flows through waterside economizer coil and then to the water in fitting feeding the unit heat exchanger.