I have a Frigidaire FFHT1835VB1 refrigerator. The fridge works properly for a day for so, then fully defrosts to room temp. I found the defrost heater is hot and the compressor is running full time when the fridge is defrosted and about 75 degrees. The ohms reading on the defrost heater is 73 ohms. The thermistor reads about 7k ohms at room temp and 19k at freezing in a glass of ice. Based on advice from this parts site I replaced the control board, but the problem continues.

Fridge is 2 years old. Coils frost evenly when cooling. When cool, the fridge and freezer temperature are accurate based on a thermometer placed in the fridge.

Any help would be appreciated!