How does a Refrigerator Work?

Michael Pollick
Michael Pollick

Ironically, refrigerators keep things cold because of the nature of heat. The Second Law of Thermodynamics essentially states that if a cold object is placed next to a hot object, the cold object will become warmer and the hot object will become cooler. A refrigerator does not cool items by lowering their original temperatures; instead, an evaporating gas called a refrigerant draws heat away, leaving the surrounding area much colder. Refrigerators and air conditioners both work on the principle of cooling through evaporation.

A refrigerator is comprised of two storage compartments - one for frozen and one for non-frozen food items.
A refrigerator is comprised of two storage compartments - one for frozen and one for non-frozen food items.

A refrigerator consists of two storage compartments - one for frozen items and the other for items requiring refrigeration but not freezing. These compartments are surrounded by a series of heat-exchanging pipes. Near the bottom of the refrigerator unit is a heavy metal device called a compressor. The compressor is powered by an electric motor. More heat-exchanging pipes are coiled behind the refrigerator. Running through the entire system is pure ammonia, which evaporates at -27 degrees Fahrenheit (-32 Celsius). This system is closed, which means nothing is lost or added while it is operating. Because liquid ammonia is a powerful chemical, a leaking refrigerator should be repaired or replaced immediately.

The condenser and evaporator in a refrigerator act as a heat exchange system that gradually cools the unit's interior.
The condenser and evaporator in a refrigerator act as a heat exchange system that gradually cools the unit's interior.

The refrigeration process begins with the compressor. Ammonia gas is compressed until it becomes very hot from the increased pressure. This heated gas flows through the coils behind the refrigerator, which allow excess heat to be released into the surrounding air. This is why users sometimes feel warm air circulating around the fridge. Eventually the ammonia cools down to the point where it becomes a liquid. This liquid form of ammonia is then forced through a device called an expansion valve. Essentially, the expansion valve has such a small opening that the liquid ammonia is turned into a very cold, fast-moving mist, evaporating as it travels through the coils in the freezer. Since this evaporation occurs at -27 degrees F (-32 degrees Celsius), the ammonia draws heat from the surrounding area. This is the Second Law of Thermodynamics in effect. Cold material, such as the evaporating ammonia gas, tend to take heat from warmer materials, such as the water in the ice cube tray.

An antique refrigerator with the compressor assembly on top.
An antique refrigerator with the compressor assembly on top.

As the evaporating ammonia gas absorbs more heat, its temperature rises. Coils surrounding the lower refrigerator compartment are not as compact. The cool ammonia still draws heat from the warmer objects in the fridge, but not as much as the freezer section. The ammonia gas is drawn back into the compressor, where the entire cycle of pressurization, cooling and evaporation begins anew.

A refrigerator should be cleaned to maximize its operating life.
A refrigerator should be cleaned to maximize its operating life.

We hope you don't forget all of this the next time you enjoy a cold glass of lemonade.

Heated gas flows through coils behind the refrigerator.
Heated gas flows through coils behind the refrigerator.
Michael Pollick
Michael Pollick

A regular wiseGEEK contributor, Michael enjoys doing research in order to satisfy his wide-ranging curiosity about a variety of arcane topics. Before becoming a professional writer, Michael worked as an English tutor, poet, voice-over artist, and DJ.

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Discussion Comments


@anon26742: You are right if the wire of the thermostat is placed in refrigerator not the freezer, it will help the compressor to turn off quickly.


I have a Kenmore 106.8576980 side by side with electronic controls on the outside front of the freezer door. The evaporator fan wasn't good so I replaced it. The lights turn on, and the fan inside turns on, but the compressor and evaporator fan won't turn on. I presume it is the control board which isn't made anymore. What about the run capacitor? I don't have a capacitor tester. Could it be keeping it from starting?


@anon 109641: I've been trying to get an answer to the same question. It's the "expansion valve". It's a brass tube that looks like a BB gun CO2 canister uniting the 1/16 in copper feed tube to the 3/8 inch condensing coils. It's approximately where you describe if you have a top freezer. A bit higher really, behind the back panel of the freezer.

I took off my back panel because mine sounds exactly as you describe and used a stethoscope to locate the sound exactly at this point. I have yet to be told why it is doing this however.


This will help me in identifying the problem in the refrigerator.


Thanks. This will help me with my science project.


Why does my old CocaCola mini fridge have a fan installed in it?


our fridge is leaking water in the front outside due to the ice maker. we turned off the water, but does the fridge need water to keep it cool?


My fridge seems to be making a bubbling sound, like air is blowing out water. It seems to be coming from the middle back about half way up of the fridge. Any ideas what it could be. Thanks.


anon59567: I don't know if you solved your problem yet, but have you tried placing like a grid where water collects and placing the vegetables on top of the grid?

that way you hold the vegetables above the ice.

and by grid i mean a porous structure.


very educational and helpful.


While the basic principles of this article are correct, few fridges these days use ammonia. Some small bar fridges and caravan (trailer) fridges use it, but it's not that common. Standard size fridges use a non-CFC gas such as R134a or R410A.


this article was so helpful!


My five year old frig freezes well, but releases water in the upper cooler area, where the thin layer of water freezes to stick the vegetable drawers to its floor. How can this be cured? Many thanks.

Cape Town, South Africa


Anon26742 - You are trying to make a perpetual motion machine, which according to the second law of thermodynamics is impossible.

Your friends are right. Even though the refrigerator is being cooled less the freezer is having to work harder. It takes more energy to freeze a jug of water than it does to keep it cool in the refrigerator. This means that that compressor is having to work longer. There are inherent heat losses in the operation of the compressor. The longer the compressor stays on the higher the losses will be.


My mom got a fridge in her bedroom and it's very cold. when I got a water bottle it was freezing cold! Why is that happening? Thanks for your help!


Klopez - Our fridge freezer was doing the same thing - I am apt to think the pump is broken - at least I have no way of finding out whether it has not. As to putting jugs of water in your freezer anon - I doubt it will help- it would probably be breaking the laws of thermodynamics if you made the fridge run more efficiently. If anyone happens to know the answer to Klopez's question I'd like to know too.


my friends and i are having a debate and i thought you might be able to help....

i am freezing jugs of water in the freezer and then transferring them to the fridge where they thaw slowly and keep the fridge from running so much...then i switch the thawed back to the freezer where they re-freeze and take frozen ones from the freezer and replace in the fridge....

my friends say that while i am helping the fridge not run so much it is make the freezer run more because it has to work harder to refreeze the jugs...

please...what is your take on this...who's right? i hope me..not that i want to be right (okay..i love to be right)..but i want to be able to continue to do this and see some results...


My mother bought a fridge for her bedroom and it has never gotten cold. It powers on but that's about it. What is the reason for that? Thanks for your help!

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