I have a 3yr old Samsung side by side refrigerator. The refrigerator side will not stay cool. It will warm up to around 55 deg and then cool back down a couple of days later. I have removed the back inside panel to reveal the cooling coils that were frosted over. The digital readout stays constant at 36 degrees even though the temperature fluctuates. I have read several different posts on the possible problem but still not sure what to do next. Any help or advice would be great.