Panasonic American style FF defrost problem

Hi Does anyone know how the Panasonic NRB54X1-WB American style side by side fridge freezer defrosts the fridge side. There is a sensor on the evaporator but no visible defrost heater and so consequently ices up after approx 2 weeks, there is a diverter valve fitted but no hot gas defrost valve fitted so how does it get rid of the ice build up. Any help would be appreciated. Thank you.