Another thing to try is to put the defroster in forced mode (see earlier post on the service manual) and then very carefully see if the heater is actually heating all the way along it's length. If it isn't, you might try replacing the defrost heating element .
I am not showing any error codes this time around. The ice built up was on the top of the coils, copper wire, and fan area. I have forced run defrost several times and it never works. When I replaced the sensor last time, the wire was not long enough to move it to the far left bottom. What concerns me is I went in and melted all the ice away and the fan noise issue came back in less than a week. I have not had time yet to go back in and see if the ice has reappeared but I am getting pretty tired of taking all my food out and putting it in my garage fridge, then taking about this fridge, melting all the ice, putting it back together again, and putting the food back it. It is sheer lunacy that this issue has not been addressed and they are expecting people with appliances that are 3-4 years old having this issue that they take care of it.
I originally called some repairmen when the issue first came about, and none of the repairmen said they would work on a Samsung fridge!! they suggested I called Sears as they are the only ones who will work on it. Hey but guess what? Sears going belly up, nobody is going to work on their stuff!
Once it has iced, forced defrost will do nothing because the heat cannot reach that far. Since you confirm that it's the top of the evaporator tube with ice buildup (like all of us), I'm confused about your sensor comment. The sensor needs to move a couple of inches to the left from the inlet copper tube to the outlet copper tube .
Our Samsung side by side refrigerator started making noises like a fan blade hitting something. It would stop when we opened the doors. Then we saw ice icoming thru the oblong holes in the interior back of the refrigerator. What the heck. It is five years old.
One thing that helped us and I wanted to share was to control the amount of humidity in the house. if you have high humidity in the house just opening the door will cause some frost to accumulate.
This is what ours did and it was the fan motor getting ice on it. The sound was the fan hitting ice. Unfortunately all they could tell us to do was unplug the fridge and let the fan thaw and then plug it back in. It would work for about 2 days then we would have to do it again. Then we found there was a way to defrost it from the panel. We did this and now the refrigerator part is not working at all. Freezer still cools though. Ours started the noise within the first year. If you’re still in warranty, you better call for service now or they will not cover it.