If the refrigerator door or freezer door was left open ,the return air next to the evaporator will frost over. Remove the back wall in the freezer and make sure both channels on the side of the coils are defrosted. This is the same thing as trying to blow air into a balloon. With the door open it will allow the air to move up. If the return air channel is blocked it can not recirculate the air. Look behind the crisper drawers on the floor,that is the vent for the return air channel to the freezer. It makes a circle, up through the damper.Then it flows to down the openings behind the crisper.