The article mentions ice building up in that old fridge, and this reminded me what I was told by a man who was fixing these things- that the condition of rubber seal and fridge not being leveled correctly can also lead to the ice buildup (if thermostat is not broken). He did not explain in deep technical details why, but said that when the fridge door is not sealing fully then the room air enters the fridge and due to different condensation point it causes moisture buildup at the coldest part. I am not sure how factual this was, since after hearing this I adjusted the fridge so the doors were always closing themselves thanks to gravity, and the ice still kept building up. I did not replace the seal though :)