Had a customer called in with a 3XAR6477GF00 Type E19TFA “American style” Fridge Freezer. It was over freezing in top compartment. When i vistited I found an obstruction on top door seal allowing air to get in all time. Took part of childs toy from door seal & it seemed to close perfectly. I also removed build up of dust/fluff etc from air vent at back & cleaned dirt off fan blade , lubricated fan bearings etc. Lady has rung back & said after a week its as bad again, a lot ice forming in freezer. Is there a defrost system in this & how does it operate?