Quoted from DerGoetz:Ice is due to your door not sealing, or air entering through your top post.
The ice stems from the humidity in the outside air.
the above is important.
also people don't understand the work involved in kegerators. the lines should be cleaned every 2 weeks (4 weeks at the worse.) Beer is a living organism, and if you don't flush/clean the lines religiously, the beer will taste badly. Also all metal fixtures should be stainless steel (not chrome plated brass.) And if the tower isn't well insulated and cold (sometimes via an internal fan), the first couple of pours will be foamy.
Kegerators are a lot of work to keep up. It sure is easier to open a bottle. Kegs were invented for high volume applications. Not basements where you pour a beer once a week. Though i really do like draft beer, the work and expense in a kegerator makes it questionable to own.