An iced-up evaporator in a commercial freezer can be caused by which of the following?

• A. Open defrost heaters
• B. Bad evaporator fan motor
• C. Bad defrost timer motor
• D. Shorted defrost termination switch

Answer: (A)

Ice on the evaporator happens when the defrost cycle fails to melt the frost that forms on the coil. The defrost heaters are what melt that ice during the defrost stage. If those heaters are open, no current can flow to them, so they won’t heat during defrost. That means the ice never melts, and it continues to accumulate on the evaporator, leading to an iced-up evaporator.

Other issues can also affect defrost, like a motor or timer not driving the cycle (a bad defrost timer motor or termination switch) or reduced airflow from a faulty evaporator fan, which can contribute to frost buildup, but the direct, immediate cause in this context is the defrost heater elements being unable to provide heat due to an open circuit.