My top freezer is not defrosting. About 1 1/2 years ago, I noticed excessive ice buildup in freezer. I cleaned out the freezer and, at that time, the fan was working fine. All seemed fine for several weeks, then I noticed that excessive moisture (large water droplets) was accumulating on the top surface of the freezer box (see image) and food was not freezing. I then set the freezer temperature to the coldest setting. This resulted in an extreme accumulation of ice in the freezer. Freezer has one shelf and most of the problems described are concentrated in the top half of the freezer compartment. The lower section is relatively ice/moisture-free. I have attached two images that display the described conditions.

I would like to check the defrost thermostat, defrost heater & defrost timer. Where are these parts located and how do I access on this model?

Any ideas on how I should proceed?

The first thing I would do is check the freezer door gasket and how the door is sealed. Also check if the hole in the back wall for ice maker water line installation is not open. Looks like warm air is coming inside the freezer.

Gene.