My Samsung refrigerator had a similar problem. It was icing up behind the panel in the back (inside) of the fridge around the evaporator. I screwed with it for several weeks until I got tired of it and did proper repair. In my case that was replacing: defrost heater, circulation fan motor and bi-metal thermostat off eBay. $20, $22 and $19 + tax respectively. I had to use a hair dryer to melt the ice around the evaporator (the part that cools the fridge) to take the defrost heater off. I also put a small area heater inside because ice had built up inside the rear wall. (the wall was ice cold to the touch even though the fridge had been off for several hours). That took another hour or so. Don’t melt the wall! Works great ever since.