Good evening, you should check the sensors by measuring the resistance, put them in a glass of cold water or a freezer and the resistance should increase, if they are damaged, the defrosting cycle will not be performed; You should also check that there is no open fuse, if so there will be no resistance voltage, I also suggest that you test the resistance live, since there are resistors that are not burned but when you turn them on they do not heat, they have lost power and you must replace it , if it is none of this, then the problem must be on the electronic board.