What Causes Ice to Form in a Freezer?

In a freezer, frost or ice forms on the evaporator coils, the component which produces a cold, low pressure gas. This gas passes through the coils. A fan distributes the cold gas and keeps the freezer cold. The coils are so cold they cause any humidity in the air to freeze onto them as ice or frost. If enough frost forms, it will affect the flow of the gas. If the flow stops completely, the freezer will not cool at all. Intense frost build up with ruin the coils and possibly affect the entire compressor operation.

How Does Frost Form on the Coils?

Mixing the cold evaporator coils with any humidity or warm air will cause frost or ice to form on the coils. An auto defrost fan is supposed to keep moisture out of the freezer. If this unit is damaged, any ice build-up will not be melted.

How Does Warm Air Get into the Freezer?

Seeping air from a damaged freezer door will cause frost on the coils. Typically, warm air rushes in whenever you open the door to your freezer. This air immediately freezes onto the evaporator coils and will cause frost if the door is left open for too long.

What About Self-defrosting Freezers?

Build up of frost in self-defrosting freezers is possible. Typically, self-defrosting freezers defrost themselves every 6 to 12 hours by turning off the compressor and turning on the defrost heater. Any frost build-up will melt into a pan at the bottom of the freezer. If any part of the compressor is damaged, the self-defrost feature will not work properly and frost will occur.

What About the Defrost Thermostat?

Passing currents flow at factory set temperatures via a bi-metal switch called the defrost thermostat. If this thermostat is damaged, frost may build up.

What Else Could Cause Frost?

Check the refrigerant levels of the freezer. Low levels will cause the compressor to improperly compress the refrigerant and could produce warm gas instead of cold gas to pass over the coils. Too much refrigerant means the liquid form of the refrigerant can leak onto the coils.

What About a New Freezer?

Running a new freezer's compressor for the 24 hours after installation is standard. After 24 hours, the compressor should only run when the temperature needs adjusting. If frost build-up occurs immediately, contact the manufacturer because a component of the compressor may be broken.

How Can You Help Avoid Frost Build-up?

Avoid putting hot foods into the freezer. Let them cool before putting them into the freezer so humidity from the foods does not cause frost on the coils. Also, if it is a hot, humid day, try to avoid opening your freezer any more than necessary.