How do the internal parts of refrigerators work?

Have you ever wondered how refrigerators keep your food chilled and frozen? The basic principles of refrigeration are actually far simpler than you might think.

By taking the time to understand the key components and mechanics of a refrigerator, you can help prepare yourself for troubleshooting common fridge issues that may come up over time. Knowing how a refrigerator works can also help you diagnose and fix problems yourself to avoid calling a repair technician.

If you need a part for your fridge or other appliances, you can find more resources including our DIY blog at AppliancePartsPros.com. There, you can enter your model number to order the exact parts you need. 

Let’s learn about refrigerators together!

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What does a fridge do?

Behind that refrigerator’s bland exterior lies an ingenious food preservation powerhouse! This cold standing box uses a fascinating bit of physics to keep your food fresh and cold, day in and day out.

Inside, refrigerant circulates through a maze of coils and absorbs heat from inside the cavities, cooling the air to frigid temperatures. Cold air is circulated to every shelf and bin.

This kitchen workhorse also filters moisture to maintain just the right humidity so produce stays crisper longer. Its chilly environment slows food spoilage and bacterial growth, keeping food at peak quality for a longer amount of time. Automatic defrosting prevents icy buildup without requiring manual chipping.

How a fridge works

How refrigerators keep a cold environment

So how can refrigerators make things cold? Heat transfer is the key principle at work here. 

Your fridge doesn’t directly produce cold air or temperatures lower than the surrounding environment on its own. Instead, it removes heat from its interior to cool it down.

The process of heat removal follows what’s known as the refrigeration cycle, which is a continuous sequence that refrigerators rely on to keep food cold. The cycle involves changing a special substance called a refrigerant between gas and liquid states to absorb and then displace heat outside the fridge.

Refrigerant itself is a specialized fluid that you can’t handle yourself. Adding or removing refrigerant requires professional assistance to avoid atmospheric releases or appliance damage.

Here are the basic stages the refrigerant goes through in an endless loop during the refrigeration cycle:

1. The refrigerant starts in the compressor as a low-pressure gas.
2. It’s compressed and condensed into a hot, high-pressure gas.
3. As the high pressure leaves the compressor, it enters the condenser coils. As it passes through the condenser coils, it will change from a high-pressure gas to a high-pressure liquid and release the heat it has stored in it as it’s moving through.
4. It goes through a metering device (such as a capillary tube) and becomes a cold, low-pressure liquid.
5. The refrigerant evaporates back into a low-pressure gas that can absorb heat in the evaporator coils, pulling heat from inside the refrigerator.
6. The gas returns to the compressor and the cycle repeats.

By constantly undergoing changes and moving through pathways facilitated by various refrigerator parts, the refrigerant transports heat from inside the unit so it becomes cooler over time.

Now let’s explore the main components involved in managing and regulating this cycle.

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Temperature regulation

It takes more than just a repeating refrigeration cycle for your fridge to maintain cold temperatures. Refrigerators also need dedicated controls and sensors to manage compression rates and cycle frequency as needed.

Temperature controls help the refrigerator vary its operation as needed while monitoring internal air and adjusting the compressor and fan activity. This keeps the internal temperature stable. 

Some older or more affordable models primarily use simple thermostats. These bi-metallic coils actuate based on detected ambient temperatures to control the cooling parts.

Many modern refrigerators include digital control boards with multiple integrated thermal sensors to provide more precise temperature regulation. Control boards can toggle between energy-efficient modes and override factory presets depending on what temperature users require.

One of the most common fridge complaints – loss of cooling – is caused by faulty temperature regulation. Some units have independent control systems for separated freezer and fridge zones. An isolated cooling problem points to controls specifically regulating that compartment.

DIY troubleshooting of refrigerator electrical control issues is limited for safety reasons. But you can check sensor resistance, continuity, wiring, and the control board display to see if any obvious open circuits suggest a failed controller.

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Air circulation

Removing heat is only half the equation. Refrigerators also require fans and ventilation flow paths to circulate chilled air for even cooling.

If refrigerators didn’t have these flow paths, cold spots would become concentrated right around the evaporator coils. Meanwhile, areas away from the center would become too warm. Total separation between the freezer and refrigerator compartments can also hinder natural convection currents.

Small electric evaporator fans inside the freezer walls promote circulation by pulling air from the fridge vents, pushing it through the evaporator coils, then re-distributing the cold air back down into the refrigerator compartment.

These simple fan motors will eventually wear out after about 5-10 years of normal use. Faulty evaporator fans are unable to establish the required airflow, which causes temperature disparities between compartments. Frozen fan blades or a weak rotation are some possible culprits.

The condenser fan also ensures the surrounding temperatures properly dissipate heat from the refrigerant lines. Without active airflow across condenser coils, critical stages of the refrigeration cycle can’t progress, and hot gas or liquid backs up.

If your condenser fan is failing, it’ll show similar symptoms as condenser coil fouling: rising temperatures, excessive compressor runtimes and general loss of cooling.

READ MORE: What Temperature Should A Refrigerator Be Set To?

Defrost cycle

The defrosting of evaporator coils also ties into the airflow. As hot air from the refrigerator compartment continuously blows across the evaporator, frost develops on coil surfaces during the gas-to-liquid transition phase.

Some frost accumulation can actually improve thermal transfer. But if left unchecked, frost buildup can eventually block airflow channels. Cooling capacity will drop once the coils are clogged with ice.

Because of this, refrigerators need melt cycles to periodically clear the frost back to acceptable levels. Timed electrical defrost heaters help fast-thaw the evaporator coil area while temporarily cutting off the compressor and fans.

The defrost timer or control board controls heater activation as well as shutting off the compressor during defrost modes. Dedicated defrost timers may sequence complete defrost/melt events around four times a day in older models. The bi-metal is a safety device that prevents the unit from overheating during the defrost cycle.

Newer refrigerators usually include adaptive defrost control boards rather than timers. Unless it’s a dual evaporator system, one thermistor will be located on the evaporator for the defrost cycle.

The control board will read the thermistor temperature and adjust accordingly based on multiple factors like compressor run time, the dispenser door being opened or the fridge or freezer door being opened.

Non-functioning defrost components like failed heaters or stuck thermostat bi-metals can lead to serious evaporator icing issues over time. To troubleshoot the issue, you can test for continuity through the defrost heaters and thermostats and check for frost buildup patterns.

READ MORE: How To Clean Refrigerator Coils

Key refrigerator components

While refrigerators may look pretty basic from the outside, they host a network of interconnected parts that are responsible for continuous heat removal. These elements essentially drive and control the refrigeration cycle:

Compressor

The compressor is the powerhouse component of refrigerators. Engaged directly with the refrigerant, the compressor pumps force the gas into a high-pressure gas state during the first stage of heat dissipation.

This conversion into high-pressure gas requires significant energy input and compression, so the compressor can get hot while it’s working. If you touch the top or side near the back of your refrigerator while the compressor runs, you’ll often feel the warmth.

The longer you use your fridge, the compressor’s efficiency may decline. In some cases, the compressor motor can burn out entirely. 

If the compressor fails, the refrigeration cycle stops and temperatures rise in both fridge and freezer compartments. If your compressor ever needs to be replaced or needs more refrigerant added to it, you’ll need to contact an EPA-certified technician to fix it for you.

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Condenser coils

After the extremely hot refrigerant is compressed, it gets condensed by passing into lengthy condenser coils near the back of the fridge.

The condenser coils are usually made of steel and cool down the heated liquid by dispersing thermal energy into the surrounding air.

A little condenser fan works hard to pull in the surrounding air and blows it across the condenser coils, helping to carry away the absorbed heat. The liquid, now cooler, keeps moving through the system. Like the compressor, the fan almost constantly runs during fridge operation. 

Dust, pet hair, and debris can gradually clog up coils over time, so you’ll need to clean them at least every six months to keep them running smoothly.

Yoder loop

As the refrigerant continues its journey, it moves to the yoder loop, which helps cool the refrigerant further. The yoder loop also prevents moisture from building on the cabinet around the doors.

Filter drier

The filter drier helps remove any moisture or debris from the refrigerant as it moves from the compressor to the capillary tube. The drier helps prevent the refrigerant from clogging the capillary tube and getting back to the compressor.

Capillary tube

Beyond condenser coils, the pressurized liquid refrigerant passes through a narrow opening called the capillary tube. This transition causes a pressure drop before the refrigerant’s next transition.

The capillary tube itself does not cool the refrigerant, but its restricted diameter helps facilitate rapid evaporating in the evaporator coils.

Capillary tubes are very narrow, so they’re susceptible to blockage issues if any contaminants enter the sealed refrigeration system. A fully or partially blocked tube will prevent liquid from flowing.

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Evaporator coils

After the refrigerant liquid lowers in pressure via the capillary tube, it reaches the evaporator coils inside the freezer compartment. Here, a combination of significantly reduced pressure and rapid evaporation into gas produces a freezing effect as the evaporator gets cold enough.

Blowing air from the refrigerator compartment across these coils also accelerates heat absorption, dropping the fridge temperature.

Frost frequently forms and then melts off the evaporator coils during cooling cycles. But if the automated defrost mechanism fails, ice buildup will eventually reduce airflow and cooling.

Leaks, holes, or restrictions in the evaporator coils will hinder the refrigeration cycle. If you’re experiencing issues with cooling, you can check for even frost patterns while the fridge is running. Uneven or isolated frost patches indicate evaporator issues.

Refrigerant lines and tubing

Several feet of tubing and piping are needed to deliver refrigerant between all the refrigerator’s components. You won’t be able to access the majority of this closed-loop line system without disassembling the machine.

However, you should be able to see portions of refrigerant tubing on the back of your fridge. These exposed refrigerant lines always need to remain intact, kink-free, and insulated so the refrigerator can work efficiently. Any damage here can result in costly repairs.

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Refrigeration efficiency

While the core mechanics of pumping refrigerant haven’t changed much over the decades, modern refrigerators have benefited from the following upgrades:

• Tighter door seals to better contain cooled air
• Adaptive defrost that applies heat only as needed
• Variable speed compressors and fans to finely tune runtimes
• Improved tubing and coatings to minimize system leaks

Internal cameras, touchscreens, WiFi connectivity, and self-diagnostics are also pushing refrigerator intelligence ever further!

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More information

Thanks for reading! If you have any appliance repair needs or projects, you can find more resources including our DIY blog at AppliancePartsPros.com. There, you can enter your model number to order the exact parts you need. Most orders arrive in two business days.

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