What causes ice to build up on the bottom of the top shelf of a stand up ice cream freezer with glass doors?

Just wondering, because ice is building up on the bottom of my top shelves in my ice cream freezer.

I work in the frozen food department of a grocery store.

I believe it is moisture that floats to the top, collects and freezes. When people open the freezer doors and the cold air in the freezer meets the warmer air on the other side. You get moisture in a teeny tiny droplet form that rises.

Do you ever notice when you open and close the doors you see mist in and out swirling around? It floats to the top freezes, and everytime someone opens the door, this process repeats. And then the thin film of ice at the top just keeps collecting and building up til you have a layer.

You can get rid of it with warm water and a wash cloth.

First of all, the ice is coming from moisture. The real question is 'where is the moisture coming from?'. Understand that the reason the ice is forming on the bottom of the top shelf is because since the moisture entering the area is warmer than the ice cream freezer (remember, hot air rises), the moisture will thus rise and stop when it hits the bottom of the top shelf. Check the seals on the glass doors. Also check to make sure insulation has not been removed around any exhaust or circulating fans. Lastly, make sure the doors are simply not left open. Note: the term 'hot air rises' does not necessarily mean it's 150 degrees, it just means it's warmer than the surrounding air.