Thought the problem was a stuck Air Diffuser. Thermistor seemed ok. Read other reviews from people who replaced the Air Diffuser. Ordered the part and it arrived a day. Removed Air Diffuser with a 1/4" nut driver, removing 3 screws. Unplugged and found old Air Diffuser Door broken. Replaced with the new one and plugged it in. Restarted refrigerator and kept thermometer in it. Refrigerator is running great.