Fridge freezing up on back wall of fridge not defrosting

well yes and no , defrosting it will temporally make it work , but main problem is there isn't proper air flow over evaporator coils id clean them with soap and water while defrosting out unit , if low airflow is allowed to continue then refrigerant gas will build to high press and escape and render unit a total replacement

If you've got ice on the back wall but 54 degrees in the front of the fridge, that points to an air circulation issue. Ensure that there is air blowing out from the back of the fridge where the ice is, and also make sure that you don't overcrowd your fridge.

you have a defrost component not working , timer , thermost , or defrost thermo

I have had this problem in the past. You will need to get the automatic defroster fixed or take all products out of freezer part of fridge. Remove back panel of freezer unplug from wall let defrost. put fan in front of it to speed proses. usually an hour or so depending on how badly frozen it is. good luck.

the defrost drain pan is plugged up,you need to defrost it and run a wire down the drain tray hole so it can drain to the bottom as it defrosts otherwise it defrosts and runs everywhere else and re freezes

1. check if the evaporator fan motor is running (inside the freezer)
2. Same for the condenser fan motor on the bottom in the back of the fridge
3. Clean condenser coils underneath or in the back of the fridge
   
4. if there is a frost on the back wall in freezer - you've got the defrost problem, check defrost heater, defrost bimetal thermostat, and defrost timer

Your defrost system has failed. Defrost timer. defrost heater. Defrost thermostat. Without a model number I can not be further help.

Ice on the back wall indicates a problem with the defrost cycle. The ice builds up and starts to choke off the air flow, so your symptoms would indicate that may be happening.

Defrost problems are usually any of the three components, the heater element, the defrost termination temp switch, or the defrost timer.

CHeck to see if there is ice built up on the back wall of the freezer. If so you have a defrost problem. Manually defrost it then take the back wall out of the frezer and check ohms on the heater if heater is ok then replace just the defrost timer and thermostat. If heater is bad replace all three.

some good stuff on youtube re
samsung fridge freezer help

also samsung diy video help