Some common causes of frost buildup in a freezer are doors being opened too frequently or being left ajar, an improper temperature setting and placing hot items in the freezer. Having too much or too little food in the unit can also contribute to frost buildup.
When the door is opened, warm air enters the freezer. Contained within the warm air is water vapor, which condenses and freezes as it cools. Leaving the door ajar and placing hot food items in the freezer increases the amount of water vapor in the unit, which results in frost buildup. Drying off packages before placing them in the freezer helps to prevent this from occurring.
If the seal around the freezer, called the gasket, is damaged or broken, this also allows warm air to enter and turn to frost. Temperature setting affects frost buildup as well. If the freezer is relatively empty, there is more air circulating, and a low temperature causes more of the excess air to freeze. On the other hand, a very full freezer can block the air vents, preventing proper air circulation that also causes frost buildup. Excess frost crystals can be removed with a warm, wet cloth and the area dried to prevent frost from reforming.