How Do Frost-Free Freezers Work?: An Easy-to-Understand Explanation

Frost-free freezers save you time and effort by eliminating the need to manually defrost your freezer—a tedious chore if you have a chest freezer.

Chest freezers are all manual defrost models while many manufacturers offer frost-free upright freezers.

A frost-free upright freezer will have the evaporator behind the back inner wall of the freezer compartment and the freezer will also have a fan that circulates the air through evaporator fins and then throughout the freezer compartment for even and efficient cooling.

In this article, we’ll take a close look at how a frost-free freezer works.

What Causes Frost in Freezers?

How Frost Forms

To understand frost-free technology, it’s important to first understand how frost forms.

• Frost develops when moisture in the air comes into contact with cold surfaces inside the freezer.
• As the warm, moist air cools, the water vapor condenses and freezes on surfaces inside the freezer, creating a layer of frost over time.

Common Causes of Frost in Freezers

Here are the common causes of frost forming in freezers:

• Leaving the freezer door or lid open—allowing warm, moist air to invade the freezer compartment.
• Loose or damaged door or lid seal. Warm, moist air will leak past the bad seal.
• Not wrapping foods properly or not placing them in air-tight containers before storing them in the freezer. Moisture from exposed food will cause frost inside the freezer.
• A failure of the automatic defrost system in a frost-free freezer will cause frost to accumulate on the evaporator fins and sometimes on the back of the liner inside the freezer.

Note: Although a frost-free freezer will automatically defrost the evaporator fins, the defrost system won’t eliminate or prevent frost from forming on surfaces and items inside the freezer due to the first 3 issues described above.

How Do Frost Free Freezers Work?

Although frost-free upright freezers won’t eliminate or prevent all frost inside the freezer compartment, their design does inherently deter normal frost.

Frost-free freezers also periodically eliminate all frost from the evaporator fins using a defrost heater.

Here are more details about how frost-free freezers work.

How Frost-Free Freezers Inherently Deter Frost

The location and design of the evaporator heat exchanger in a frost-free model helps prevent frost from forming on inner liner surfaces.

Why Frost Forms on Liner and Shelf Surfaces of Manual Defrost Freezers

Here are the reasons why frost builds up on freezer liner and shelf surfaces inside chest freezers and manual-defrost upright freezers:

• In chest freezers, the evaporator lines are located just outside the inner liner of the freezer compartment so frost and ice will form across the sides and bottom of the chest freezer compartment.
• The same thing happens in upright freezers. Some upright freezers run evaporator cooling lines through freezer shelves as well as just outside the inner liner of the freezer compartment.

Why Frost Normally Doesn’t Build Up on Frost-Free Freezer Liner Surfaces

In a frost-free freezer, cooling occurs in the evaporator. The evaporator fan circulates cold air throughout the freezer compartment.

Because of this design, most of the frost that forms in a frost-free freezer is concentrated on the evaporator fins. The evaporator fins are periodically defrosted automatically by a defrost heater in the automatic defrost system.

Unless a large amount of warm, moist air enters the freezer because of one or more causes discussed above, you typically won’t see much frost inside a frost-free freezer except when you fail to tightly wrap or seal up moist foods.

The Automatic Defrost System – Eliminating Frost from the Evaporator

Frost that normally forms on the freezer evaporator fins will be periodically melted off by the automatic defrost system.

Here’s how the automatic defrost system works:

1. The defrost timer or electronic control board initiates the automatic defrost cycle based on elapsed time since the previous automatic defrost cycle was completed. The electronic control board in some freezers use more input such as sensor readings as well as elapsed time to determine when to initiate the automatic defrost cycle.
2. The control system stops the compressor and the evaporator fan to start the defrost process.
3. The control turns on the defrost heater under the evaporator to melt frost and ice off of the evaporator fins.
4. Condensate water from ice and frost melting off the evaporator fins drips into a tray below the evaporator and then drains down into a collection container next to the compressor in the machine compartment at the bottom of the freezer. That water evaporates due to the heat from the compressor and air circulation through the machine compartment.
5. The control shuts off the defrost heater or a thermostat shuts off power to the defrost heater once all frost is melted off the evaporator fins.
6. The control starts the compressor and evaporator fan to resume normal cooling.

This defrost routine typically takes around 30 minutes to complete in most frost-free freezers.

The automatic defrost cycle repeats every 10 to 20 hours in most models.

Troubleshooting Frost-Free Freezer Defrost Problems

Find and Fix the Cause of Excessive Frost

When you see excessive frost in your frost-free upright freezer, check for the common causes of frost listed above and fix the cause of warm air leaking into the freezer compartment.

If the freezer door gasket is damaged, you can follow the procedure in this helpful video to replace that seal:

Note: The video shows how to replace a refrigerator door gasket. The procedure for replacing a freezer door gasket is the same as the one shown in the video for many frost-free freezers.

If you’re unable to replace the freezer door gasket on your own, schedule freezer repair service and we’ll send a Sears Home Services Technician to your home to replace the door gasket for you.

Troubleshooting the Automatic Defrost System

A failure in the automatic defrost system of a frost-free freezer will often result in cooling problems because the air passages between evaporator fins get clogged by frost and ice that isn’t being properly melted off by the defrost system.

You can often fix this type of cooling problem temporarily by unplugging the freezer or shutting it off for several hours and leaving the freezer door open until ice melts off the fins. You may need to safely store food that may spoil during this troubleshooting step.

The freezer may resume normal cooling after this process. If the automatic defrost system does indeed have a problem, the frost and ice will eventually build up again and inhibit cooling. When this happens, you’ll likely need to schedule freezer repair service to have the problem fixed by a technician.

If you’re confident in your DIY troubleshooting and repair skills, you may be able to find and fix an automatic defrost system failure on your own. The automatic defrost system in a frost-free freezer is often the same as the defrost system in a refrigerator. Follow the steps in this popular YouTube video to troubleshoot the defrost system in your freezer:

Now that you know practically all there is to know about a frost free freezer, you’ll be able to recognize problems with frost and cooling as well as keep the freezer running smoothly and efficiently.

Of course, you’ll also have Sears Home Services standing by as your backup in case you need any help. We know appliances and we’ll help you with anything that you need in your home.

Trust us to help you keep your entire home running smoothly.