Removed bottom bin and noted ice in the vents to evap coils. Removed back cover of freezer section and used hair dryer to manually thawed large ice block. Used electric meter to confirm defrost element and thermostat were good. Noted damper door was closed and would not open. Damper motor was bad. Opted to replace damper assembly and thermistors. Replaced parts and refrigerator is working great. I decided to open damper door manually in order to use refrigerator while waiting on parts. Taped damper vent off at night to prevent items from freezing.