Our Kenmore refrigerator section is not getting cool. The freezer section is fine. The cold air isn't blowing through the air vents in the refrigerator section. Actually no coolness comes out of the air vent in fridge section until the freezer air vent is covered or freezer door is opened. There is a great deal of frost on the back of the freezer. Could this be a clue to what is wrong? THANKS!