In order to take a closer look behind the reasons for evaporator freeze-ups, we must first look at how moisture builds on the evaporator. As the freezer compartment temperature drops, warm air and moisture from the product, as well as other areas, are pulled into the evaporator compartment. This moisture will condense and freeze on the evaporator, creating a partial or full block of ice and restricting airflow.
This frost or ice buildup is a normal part of any freezer operation, and is removed by using heated defrost cycles at timed intervals. During normal operation, the amount of this buildup should not get to the point that problems will occur. However, in some abnormal circumstances, it can lead to problems.