Samsung RB1855 refrigerator barely cool. Freezer works fine

[Nettie]

 The freezer works fine but the refrigerator s barely cool. I set the temp to lowest and tried power cool but it's still barely cool. I cleaned out underneath and opened the back at the bottom to clean out all the yuck. Checked the freezer to refrig vents aren't blocked. The fan in the back is running but there doesn't seem to be much air flow inside the refrigerator. I understand there is a self diagnostic method using the front display but don't know how to do it. Any help?

[domain]

Have to check fridge evap. If it is around 50 degrees in fridge I would suspect airflow issue, usually ice

[Nettie]

Where would the ice be ? There is no ice or frost anywhere that I could see.Nothing seems to be blocking. I blew air through the vents freezer to fridge and could feel it. This is a counter depth refrigerator. Do I need  to remove the entire back?t I apologize if I seem ignorant ...I am! 

[domain]

There are no vents connecting FRIDGE AND FREEZER. Behind the panel on back wall of fridge. No apologies needed. You must be careful removing it. Might wanna call a pro

[mike243]

Is there water under the crisper drawer? drains get clogged and the evap motor pulls the moisture up and ice stops the fan,good luck

[Nettie]

   I didn't mean to say that the fridge and freezer vents were interconnected but I see that's how I made it sound. Poor choice of words. Anyways there was no water under the crisper drawer. I took the interior back panel off and sure enough it was covered in ice. Got it defrosted and put back together. It's working fine now. Now I just need to figure out why it happened. Ive had the fridge for about 4 years. Is that a maintenance thing where every so often you have to open it up, or is there a defective part somewhere?

[mike243]

Defrost thermistor or limit,with out using a meter you can just replace both and probably fix it,when the thermistor gets out of range it will think the evap isn't cold enuf and never start the defrost cycle