Hi @vinchenzzi
The evaporator unit being all iced up is not good. This means that there is an auto defrost problem somewhere. This could be a faulty defrost heater, blocked drain leading from under the evap unit to the evaporator pan under the compartments, faulty defrost thermister or worst case a faulty control board.
Ice buildup on the evap unit can affect the cooling efficiency of the refrigerator.
Most refrigerators go into their auto defrost cycle once every 8-10 hours. The defrost cycle lasts for about 20-25 minutes. When this occurs the compressor and the evap. fan are both turned off and the defrost heater is turned on to melt the ice buildup on the evap unit. The temperature in the compartments (refrigerator and freezer) will rise. When the defrost thermistor signals that the set temp to end the defrost cycle is reached, the heater will be turned off and the compressor and fan restarted to cool things down again. So if the auto defrost was working OK there should be no ice build up on the evap unit. A frosting of ice on the evap unit can happen, especially on humid days, but this would be cleared by a properly functioning defrost cycle.
Given that there could be many reasons for what is happening with the refrigerator, the quickest and easiest thing to do it to run the diagnostics for the refrigerator. This will test all the functions and most of the components e.g. heater, fans, thermistors (freezer and refrigerator), compressor etc and if there is a problem then an error code will result indicating what is wrong.
Unfortunately I cannot find a free service manual online to help you and I don’t know how to do this for your particular model. The service manual details how to get into the Diagnostic mode and run the tests and also what any error means. Service manuals (supplier example only) are available to purchase however. Search online for RF266AEPN service manual, to find suppliers that suit you.