I can understand your frustration and understand why are you getting ice buildup on your evaporator cover panel and after doing checks and replacing parts you are still having problems I’m having the same on the back evaporator cover is frosted over and I hear my evaporator motor making noise also.
My evaporator fan motor is working properly but after defrosting it will take about six hours until I hear that noise coming from the evaporator fan and I have ice buildup on the back panel.
After diagnosis and checking all the sensors to relays the motor and the heater power working properly and yet I’m still having this problem.
And by trying to put insulation to warm up your upper part of your freezer is not really a fix for the problem or to figure out what is the problem after thinking I come to a conclusion I am still getting water condensation buildup I’m back panel and after looking and thinking about this problem I’ve come to realize on my GE French door refrigerator I have an icemaker which requires water to make the ice obviously and after inspecting the icemaker I noticed a small leak coming from the line going into the icemaker going down the back wall which was causing my problem…. I am not a service technician and I don’t know too much about Samsung but for the GE that I have that was the cause of the problem it was very hard to detect especially when the icemaker was in place and only after I had everything removed I noticed..
I hope this helps.