The moisture drain tube to the water evaporator pan may become plugged with debris and gummy substances. When that happens, water created in the defrost cycle cannot drain out. It overflows and leaks down, covering the freezer floor, and then during the refrigeration cycle, it turns to ice. To remedy the problem, unplug the unit and let it defrost. Clear the drain line of debris by shooting a stream of air into it or simply by blowing into it.
A similar thing happens if the unit is not seated level and does not allow the drain water to reach the opening of the drain tube. In that case the water accumulates to the point that it overflows and runs down the insides of the walls, misses the drain pan, and forms a puddle under the unit. (See fig. 3)
Most models come with a heating element around the top of the drain tube. If that element stops working, ice will form in the opening and cause one or more of the symptoms mentioned above. Test the heating element with an ohmmeter as described in “Testing the Defrost Heater.”