The freezer alarm on my old Smeg American style fridge freezer periodically goes off. It’s generally weeks between these events. The display indicates the temp is -20 as usual despite the alarm indicating inside the freezer the temp is rising. The rising temp is supported by the food stuffs in the freezer starting to thaw. I’ve had the back panel off and there was an ice buildup adjacent, around a cluster of wires from the back of the fridge, to the fan causing the fan to operate loudly. The ice was on the fan side not the evaporator. I removed the ice. The evaporator was clear as was the drain point below. As a remedy I turn the appliance off at the mains and leave it for a few minutes. Turning the power off and on with a pause seems to cure the problem. I would like to solve this riddle if possible. Lately the alarm has gone off in the middle of the night but this may just be a cyclic issue.