An exemplary embodiment of a diverter valve system includes a valve body defining an internal chamber having at least first, second and third ports, and a first valve seat associated with the first port and a second valve seat associated with the second port. A valve shaft structure includes an internal shaft portion positioned within the internal chamber, the valve shaft structure configured for rotation about a valve axis through a range of motion. A diverter structure includes a diverter face portion configured to seat against the first valve seat when in a first rotational position and against the second valve seat when in a second position, and a mounting portion configured to mount on the internal shaft portion of the valve shaft structure.