Samsung Refrigerator freezing up

Refrigerator & Freezer Repair
1

Brand: Samsung
Model Number: RF18HFENBSR
Main Symptom: Refrigerator is freezing up.
What happens & when: The refrigerator Coils are freezing up. I have replaced the heater, back panel, and drain tubes already. I have also cleaned grates on back. I believe that it is not going into defrost mode. The Freezer is fine and I cleaned the gaskets also on both.

Error Code (if any):
Parts or tests already tried:
Photos / video link:

2

With the coils icing up, check the defrost thermistor and bimetal. If they both check ok then the control board will be the issue.