Solving freezing vent in refrigerator

you may have a badly closing door seal. if you get a small air leak into the refrigerator, the air keeps the fridge warmer than it wants to be, so it keeps running the compressor to try to cool the fridge. as it runs, condensation forms internally and will build up in certain areas, and freezes into ice. i would have a look at your door seal. just take a thin flat blade of plastic (don't use steel as you can scratch the seal or the mating face) and slide it around the contact point of the seal and the chassis. you should feel slight resistance everywhere, indicating the mating of seal and mating face. anyplace you have a drop in resistance, the seal is letting air into the fridge. this is usually fixed by levelling the fridge properly. the raising and lowering of the fridge corners will make the chassis flex back into a truly rectangular box so that the door is parallel on all four edges.

The vent that is getting iced over is how the compartment gets the cold air from the evaporator coils. I'm assuming that if the problem with ice build-up is a recent issue then the automatic defroster may be out. If this model is a "frost-free" type than check either: 1) the defrost heater or limit switch 2) the defrost timer. These components are usually buried deep within the bowels of the appliance and vary in form and shape making it hard to describe what to look for. Look for the timer close to the thermostat controls. The limit switch is usually on the evaporator coils and is a round metal cylinder with wires attached. Lastly check the drain line is not blocked and allowing defrosted water to back up and become frozen.