How Refrigerators Work
How Tech Works

How Refrigerators Work

Refrigerators crap out all the time—one of our most-popular forum posts is about a refrigerator not working properly, if that tells you anything. Here’s how a refrigerator works, so you’ll be able to troubleshoot and repair most issues that come up.

Refrigerators seem like complicated machines, especially considering they’re one of the biggest appliances in your home. Indeed, many newer refrigerators come with all sorts of advanced technology, but the core functionality still relies on concepts from the mid-1800s to keep your milk from spoiling too soon.

Believe it or not, refrigerators don’t add cool air to the space inside. Rather, they remove heat by running refrigerant (most commonly tetrafluoroethane) through a hermetically-sealed system of copper tubes and coils, relying on compression and decompression to raise and lower the refrigerant’s temperature, thanks to Gay-Lussac’s law, which states that the pressure of a gas is directly proportional to its temperature, as long as the volume remains the same.

The system in a refrigerator includes four main components: a compressor, a condenser, a throttling (or metering) device, and an evaporator.

The Compressor

If you’ve ever peeked behind a refrigerator and noticed a globe-like device at the bottom, that’s the compressor. It’s responsible for pumping refrigerant through the system, but most importantly, it compresses the refrigerant (hence the name).

Whenever you hear your refrigerator kick on and make a buzzing noise, that’s the compressor’s motor, which isn’t unlike the one on your lawn mower—just way smaller and powered by electricity instead of gasoline. It sucks in refrigerant left over from the previous cycle, which is in a warm, gaseous state from absorbing heat.

That heat needs to be dumped outside the fridge and the refrigerant cooled down. However, in order to do that, you need something colder to cool down the refrigerant. In this case, it’s the ambient air in the room, which is where the compressor comes into play.

The refrigerant is compressed inside the compressor motor’s piston chamber, which increases its pressure. This makes the refrigerant hotter than the ambient air in the room. From here, the refrigerant enters the condenser to be cooled down.

The Condenser

The condenser is a set of coils that the refrigerant flows through after exiting the compressor. During this phase (with the help of a cooling fan), heat radiates into the ambient air, cooling the refrigerant and condensing the gas into a liquid. It’s similar to placing your hand over a boiling pot of water—when the steam hits your hand, it’s cooled down and turns back into a liquid.

This process cools the refrigerant after the previous cycle, but even after leaving the condenser, the refrigerant is still warm and needs to be cooled down further in order to absorb more heat the next time around. That’s where the throttling device comes in.

The Throttling Device

In order to rapidly cool down the refrigerant, it needs to be decompressed. This will lower its pressure, and thus, its temperature. The throttling device does this job.

The circle of [refrigerator] life! Illustration by Daniele De Pietri, DensityDesign Research Lab

The throttling device adds resistance to the high-pressure flow of refrigerant making its way through the system, quickly lowering its pressure and partially evaporating it (called flash evaporation). Now a mixture of liquid and gas, the refrigerant’s temperature is much cooler, so it can absorb more heat from inside the fridge.

Just as important, the throttling device also throttles how much refrigerant it allows to pass through at any given time. This makes the refrigerant more efficient during the next stage.

Throttling devices come in the form of a thermal expansion valve or a capillary tube. The former is more sophisticated and more efficient when temperature changes occur (such as when placing a hot tub of leftovers in the fridge), as it can open or close the valve to varying degrees. The latter is simpler and cheaper to fix (it’s nothing more than extremely-thin tubing), but isn’t quite as efficient as an expansion valve.

The Evaporator

The evaporator is hidden inside the refrigerator, behind the plastic cover toward the back.

At this point, the refrigerant’s temperature is much cooler than the inside ambient temperature of the fridge. The next step is for the refrigerant to flow through the evaporator, which is yet another set of coils. But this time, these coils are located inside the refrigerator instead of outside.

Thanks to thermal equilibrium, anything inside the refrigerator that’s warmer than the evaporator coils will give up its heat to the coils. The cold liquid refrigerant suddenly starts to warm up again as it absorbs heat from the contents of your fridge, evaporating back into a gaseous state.

The refrigerant leaving the evaporator gets sent back to the compressor to start the cycle over again.

In some refrigerators, the evaporator will be located in the freezer section. An evaporator fan will circulate air over the evaporator coils, as well as push air from the freezer into the refrigerator, with a damper being used to control the amount of air flow. Some refrigerators will have two evaporators hooked up in series: a larger one in the freezer and a smaller one in the refrigerator.

Common Refrigerator Problems

A lot can go wrong with a refrigerator, but there are a small handful of issues that are more common than others.

The most common of the common is the fridge not cooling enough. Or the freezer may still work fine, but the fresh food section is not. Or the refrigerator is constantly running in order to keep the inside at the proper temperature. These are common problems because there can be any number of factors at play:

  • The easiest thing to check for first is making sure that the doors seal up nice and tight when closed. If not, you’re letting warm air into the fridge! Inspect and replace any door seals as needed.
  • The condenser coils could be dirty, which prevents heat from dissipating. A quick cleaning with a vacuum can often do the trick.
  • Either the condenser fan or evaporator fan might be broken, which can decrease proper airflow and prevent proper cooling in either situation.
  • The defrost heater surrounding the evaporator coils could be broken, which results in excess frost buildup on the coils, preventing heat absorption.
  • The damper could be stuck closed, preventing cold air from flowing into the fresh food section.
  • Rarely, there could be an electrical issue with the control board (which sends voltages to components that need to be turned on or off) or the thermistor (which monitors the temperature and reports it to the control board).

If, on the other hand, you have an abnormally noisy refrigerator, that likely points to a failing motor somewhere in the fridge—either the compressor motor or a fan motor, in which case the bearings are probably going bad or the motor is close to burning out.

A fan motor is easy enough to replace (usually a simple swap once you remove any panels), but any component that’s a part of the sealed refrigerant system has to be desoldered in order to remove it, and soldered back on when replacing. And since that process introduces air into the system, it has to be vacuum-pumped and charged with refrigerant after the repair, which requires specialty tools. This kind of repair you generally want to leave to a professional.

But even if it’s a repair that you aren’t comfortable doing yourself, it’s at least comforting to know exactly what the problem could be and understanding how it occurred. That way you have more confidence when it comes time to talk to a professional repair technician.

Are you about to embark on a DIY refrigerator repair journey? Document it and share it with the world by creating a repair guide on iFixit! Our refrigerator category is somewhat lacking, but you can help improve it!

Title image by Jose Soriano/Unsplash