Frost buildup in freezers and refrigerators happens when warm, humid air is rapidly cooled by the refrigerator. Moisture condenses from the humid air and quickly freezes, forming frost. The process happens normally around the refrigerator's evaporator coils, and it can also occur inside the refrigerator or freezer when the proper flow of air within the unit is disrupted.
In a frost-free refrigerator, frost buildup on the evaporator coils is eliminated by an automatic defroster system. The system is controlled by a timer which begins a defrost cycle at regular intervals. When the timer activates the system, a heater turns on and melts frost that has built up on the evaporator coils. A thermostat detects when the coils have reached the proper temperature, and when they are sufficiently warm, the heater turns off automatically.
If any of the components of the defrost system, including the timer, heater or thermostat, fails, the system will not work properly, and frost will continue to build up on the evaporator coils. In this case, the system will need to be serviced by a technician.
When cool air is not able to flow properly around the refrigerator or freezer compartment, frost and ice can build up in areas where cold air comes into contact with warmer, more humid air. To prevent this problem, do not block the cool air vents, which are most often in the back of the refrigerator and freezer compartments, with food items.
An overcrowded or densely packed refrigerator or freezer can also hamper air flow and cause frost problems. Do not put items against the back wall of the refrigerator or freezer, and allow as much space as possible between items so that air can flow freely around them.
Improper temperature settings can lead to ice buildup inside the refrigerator. If the temperature control is set too low, food may freeze. If the temperature is set too high, condensation may form and then freeze on food or in the bottom of the compartment. Adjust the refrigerator's temperature controls to eliminate these problems.
If the refrigerator or freezer doors are not closed and sealed properly, outside air can infiltrate the compartments, and when humid outside air meets cold air inside the compartment, frost and ice are likely to form. Make sure that doors are not prevented from fully closing by items inside the refrigerator and that the gasket seals around the edges of the door are not torn or dirty. Clean dirty gaskets with a soft cloth and warm water, and promptly replace any damaged gaskets.
In some refrigerator models, warm air can enter the freezer through the ice maker if the flap that seals the ice maker opening does not close properly, and the infiltration can result in frost buildup. Check the flap to be sure that it is not blocked by ice or debris, and remove any blockages.