Icing up every 4 days

Hi Stewart525, As long as your defrost heater is good, and has continuity, then we will move on from them. Make sure that your evaporator fan motor is working also. If fan motor is functioning, in most cases, your mother board is most likely the cause. What you can do is pull the refrigerator out, and remove the back square panel behind the unit, this is where your mother board is. Unplug the refrigerator and remove all harnesses, remove the board by depressing the 4 white pins holding it on, and inspect the back of the board. A lot of the time, you may be able to visually see that there is a burn spot on the back of the board. Usually directly on the other side of where the black relays lie. Although, the burn marks are not always present, that does not mean the board is necessarily good and in working order. In this case it is most likely the root of your problem. Please provide a FULL model number if you have any other questions. It is most likely located in the fresh food side on the right or left wall towards the top of the unit. Attached is a link to the mother board and a video of how to access and replace mother board. I hope this was helpful! If you have any other questions, please feel free to ask! Thank you, Tony-AceTech52