Product review (5 stars): Samsung RF217ACPN 33", Need this and two other parts to fully address problem
I have a 7 year old Samsung 33" bottom freezer, french door refrigerator, model Samsung RF217ACPN.  This gist of this post is to tell you that you need to swap out three (3) parts total if you are experiencing ice build up in the back of your Samsung Refrigerator possibly along with water in or under the lower drawers.  As I understand it, nearly all the Samsung refrigerators built in the last decade use the same cooling and defrost mechanism.  Some models do not have a manual defrost mode, and you will need to unplug the refrigerator to actually melt the ice build up.

About a year ago, the vegetable crisper drawers began to fill with water.  This indicated a drain freezing problem which necessitates the thawing and replacement of an improved drain heater extension part "SAMSUNG CLIP DRAIN EVAPORATOR REFOEM Original Part: DA61-06796A (https://www.amazon.com/gp/product/B008KFG9NO)"  This has a longer drain extension that takes heat from the heating element and extends it into the drain hole to prevent icing.  Samsung realized their original clip was deficient and released this improved retrofit.  This is not a question of if it will happen to you, it is a question of WHEN.

I noticed that the rear of the refrigerator also began to show ice from some of the holes.  Normally a 48 hour defrost takes care of it but eventually it would build up to the point that the spinning fan starts to hit it.  This icing indicates a problem with your defrost system.  This item is the "Samsung Thermo Bimetal - Prote Part # Da47-00243K (https://www.amazon.com/gp/product/B001ICO2H6)" is one of two thermo sensors that you should replace.  This black wire sensor senses the high temperature heating conditions of the heating element and stop it before it melts your fridge.  This bimetal sensor is a more likely culprit to go bad as the resistance degrades as it ages with heat cycles eventually preventing your heating element from heating to any useful level to actually melt the frost on the coils.  The black sensor may need to be spliced into the existing wiring, so be prepared if your model requires simple wire splicing.  Yes the black high temp sensor does go bad, but there is another sensor that also goes bad that you should replace at this same time.  The item "Samsung DA32-00006S Refrigerator Defrost Sensor (https://www.amazon.com/dp/B001KGPERM)" is the second of two thermostat sensors for the defrost system.  The other yellow cord sensor senses the low temperature frost conditions on the coils.  You should move the yellow defrost sensor from the tube on the right to the more central tube on the left.  This helps with sensing the ice that grows from the middle outwards.  You should replace BOTH defrost sensors as a pair to ensure that you don't revisit the problem in a month.

One last tip is for you to extend the front floor riser pegs and lift the front wheels off the ground.  This will ensure that the defrost liquid drains properly towards the rear.  Not all kitchen floors are level and if it is slanted forward even a little bit, the water can leak out the front vents and frost over after the defrost cycle.

So far, I have been frost free and the crisper drawers are dry for months.  Don't just replace this one part, you need to replace three parts in total.  All the components are relatively inexpensive.  Good luck in fixing your poorly designed and defective Samsung refrigerator.  I wanted to share this so that others will not have to go through the months-long nightmare of addressing this issue piece by piece.