Frost-free refrigeration is standard in modern refrigerators. As the frost builds up on evaporator coils, these types of refrigerators make occasionally opening up the doors and melting away the ice unnecessary. Instead, frost-free units melt it by themselves and drain the water into a catch pan every few hours. But the system must be working properly to make this happen. Commonly frost-free refrigerators freeze up when one of several components is not functioning properly.
One of the most common reasons a frost-free refrigerator system will begin to accumulate ice and freeze up is a malfunction with the defrost heater, which gets a signal from the thermostat to turn on periodically to heat up the area around the evaporator coils. This melts the frost, and the water drains out through a tube into a catch pan where it evaporates. When the heater fails to work properly, the frost continues to build up and eventually restricts airflow throughout the refrigerator, causing condensation to begin turning to ice; eventually the system may be frozen and covered in ice throughout the freezer compartment and potentially on the walls of the fresh food compartment as well.
Worn gaskets on the refrigerator and freezer doors can lead to icing and freezing, even in a frost-free system. Usually the ice will appear on the walls of the freezer and refrigerator and not on the evaporator coils in this instance. While the refrigerator may continue to operate normally for awhile, this ice formation will eventually block off the vents that allow cold air to circulate from the freezer to the refrigerator compartments. Condensation build-up is the primary cause because warm air is leaking into the refrigerator. Also, as cold air escapes, it makes the compressor work harder to keep the unit cold, which will significantly increase energy bills.
Defrost Limit Switch
The defrost limit switch could cause a frost-free refrigerator to freeze up. This mechanism, also known as the defrost thermostat, limits how cold the refrigerator can get before it signals the defrost heater to kick on and melt the frost by raising the temperature. If there is a malfunction in the defrost limit switch, the heater will not come on, and frost and ice will begin forming in the refrigerator.
Sometimes you will find ice forming inside the refrigerator because there is a water leak. When the frost-free system kicks on and melts frost, the resulting water runs down into a drain tube that carries the water to a pan in the bottom of the unit. If a particle of food or a bit of ice plugs the drain, the water will overflow and run into the refrigerator compartment below. The presence of extra water in the freezer compartment above the drain will begin turning it to ice, which will interfere with air circulation, which then begins freezing the water in the compartment below. Often you'll find pools of water or ice in the bottom of the refrigerator and in vegetable drawers when this happens.