I just got a used Beko CDA543F frost free refrigerator. It seems to work fine except I have noticed a slight ice buildup of fluffy ice on the inside of the rear free fridge wall in a perfect rectangle shape that I am guessing is exactly where the evaporator is behind it. It goes if I turn the thermostat down to 1, which apparently starts the defrost heater. But it re-appears when the thermostat is turned back up. After watching it after being on all night there are also frozen water droplets so I would guess that the defrost heater is working and these were droplets that were formed when the defrost heater melted the ice but re-froze when the defrost heater switched off. It is really not that thick a layer at all. I just wondered is this normal as I cannot seem to find much information on the internet. There is no frost in freezer at all. Thanks for any help.