Frost buildup in freezer and ice maker not making ice

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Brand: SAMSUNG
Model Number: RFG237AARS
Main Symptom: FROST BUILDUP IN FREEZER AND ICE MAKER DOES NOT PRODUCE ICE
What happens & when: After a repairman defrosted the unit, replaced the “main board” , the “Defrost thermostat” and “Temperature sensor” the unit worked fine. Over the next 3 months frost build up again and the icemaker started working. We called the company back but they said they only warranty repairs for 90 days so we were just over by a few days. With the $600 we had to pay for the service we are not able to call another company to come out. Can you walk me through what else I should replace to get us up and running again. Any help is greatly appreciated. Error Code (if any):

Photos / video link

Hello, the defrost system is made up of a control, a heater element, and a defrost thermostat or defrost terminator. If all those parts were replaced, then one of them as failed again. The bi-metal should have continuity when it is tested with a meter. The element should show resistance when tested and the board should be able to be put manually into defrost cycle.

Thanks for the quick reply David. I am not familiar with doing any continuity testing so I was hoping you could let me know what parts to change out. Your company has excellent videos, so I think I can install the parts without any problem. Of course, I would not hold you to any suggestions not making a difference, but I am in kind of in a bind because I paid the first repairman so much. I appreciate your time and patience. Sincerely, Frank PS. Just making sure you saw the pictures I attached because I would like to know why that block of advice is formed on the wall of the refrigerator?