This 7-8 year old F/F cycles HOT and COLD approx every 7 hours and completely defrost the F/F (so the customer says)
The F/F is mechanical no PCB inside I have replaced the defrost timer with no joy.
The F/F has the freezer on the left and fridge on the right hand side, a mechanical flap at the top to the freezer lets the cold air into the fridge. All the controls including the defrost timer are in the top of the fridge.