Freeze! Don't move or rather melt: How a Refrigerator works and the common faults that stop it cooling

The Silent Sentinel in Your Kitchen

Day and night, the refrigerator hums quietly, preserving food, preventing waste, and keeping life fresh. 

It’s easy to take this appliance for granted, until one morning you open the door and find your milk warm and your vegetables limp.

Behind that silent hum lies a masterpiece of applied physics and engineering. One that constantly moves heat out of the box to keep its contents cool. 

To understand why your fridge sometimes misbehaves, it helps to know the principles and components that make it work in the first place.

Let’s open the door and peek inside the science of cooling.

 

1. The Science of Refrigeration

Refrigeration is based on one elegant idea, which involves, heat always flowing from a warmer area to a cooler one, and if you can reverse that process artificially, you can move heat out of an enclosed space, like your fridge.

In short, it is the same thing as feeling cold from a rainy day, and entering a warm bath or shower. The heat from the warm water travels towards your body.

To do that, a refrigerator uses a refrigeration cycle, which involves compressing and expanding a fluid (the refrigerant) to absorb and release heat.

The four main stages of this cycle are:

1. Compression – the refrigerant gas is compressed to high pressure and temperature.
2. Condensation – the hot gas releases heat to the surroundings and becomes a liquid.
3. Expansion – the liquid refrigerant expands rapidly, dropping in pressure and temperature.
4. Evaporation – the cold refrigerant absorbs heat from inside the fridge, cooling it down.

Then the cycle repeats, continuously pumping heat out of the refrigerator’s interior.

 

2. The Key Components and How They Work Together

Let’s trace that cycle through the major parts of your fridge.

a. The Compressor. The Heart of the System

The compressor is often called the refrigerator’s heart because it keeps the refrigerant circulating.
It’s a sealed electric motor-pump assembly that compresses low-pressure refrigerant gas from the evaporator into a high-pressure, high-temperature gas.

As the gas is compressed, its temperature rises (just like a bicycle pump gets hot when used). This hot gas then flows to the condenser coils.

Common compressor types include:

Reciprocating piston compressors (common in domestic fridges),

Rotary and scroll compressors (more efficient, found in high-end or inverter models).

b. The Condenser Coils and Shedding Heat

These are the black or metallic coils you might see at the back or bottom of the refrigerator.
As the hot, high-pressure gas passes through, it releases heat to the surrounding air and condenses into a high-pressure liquid.

A fan often helps dissipate this heat in modern fridges, especially frost-free models. The process is like steam cooling into water. Same substance, different state.

c. The Expansion Device and Dropping the Pressure

Once the refrigerant has turned into a liquid, it passes through a capillary tube or expansion valve.

This narrow passage causes the liquid to expand rapidly, lowering its pressure and temperature. The refrigerant is now a cold, low-pressure liquid–gas mixture ready to absorb heat inside the fridge.

d. The Evaporator and where the cooling happens

The evaporator coils are located inside the freezer compartment or behind its back panel.
As the cold refrigerant flows through these coils, it absorbs heat from the air inside the fridge, causing the refrigerant to evaporate back into a gas.

A circulation fan distributes this cooled air evenly across shelves, maintaining a stable temperature throughout.

e. The Thermostat and Sensors and Temperature Control

A thermostat or temperature sensor monitors internal temperature and signals the control board to turn the compressor on or off.
Modern fridges use electronic thermistors for precise control, while older ones rely on mechanical thermostats.

f. The Control System aka The “Brain”

In newer digital models, a microcontroller-based control board coordinates the compressor, fans, and defrost cycle.
It may also adjust compressor speed (in inverter refrigerators) for better energy efficiency and quieter operation.

 

3. The Defrost System: Preventing Ice Buildup

In older refrigerators, you had to manually defrost, which involves turning the unit off and waiting for ice to melt.

Modern frost-free models use an automatic defrost system consisting of:

A defrost heater (a small heating element on the evaporator), a defrost thermostat or sensor, and a timer or control board to manage the cycle.

At intervals, the system briefly warms the evaporator to melt frost, and the water drains out through a tube to a small tray near the compressor, where it evaporates.

Without defrosting, ice would insulate the evaporator coils, reducing cooling efficiency and airflow.

 

4. Common Refrigerator Faults and Their Causes

a. Refrigerator Not Cooling Properly

Possible causes:

Dirty condenser coils restricting heat release.

Faulty condenser fan motor.

Low refrigerant level (possible leak).

Malfunctioning compressor or start relay.

Thermostat or temperature sensor failure.

Quick checks:

Make sure the fridge isn’t pushed tightly against the wall, as it needs ventilation.

Clean the coils with a soft brush or vacuum.

Listen for the compressor, if it hums briefly and clicks off, it could be a start relay or capacitor issue.

Low refrigerant levels or compressor faults require a professional with the right tools and refrigerant handling certification.

 

b. Freezer Works, But Fridge Section is Warm

This is one of the most common complaints.
Causes:

Blocked air passage between freezer and fridge section.

Faulty evaporator fan motor not circulating cold air.

Defrost system failure leading to ice buildup on coils.

DIY fix:
If you notice frost forming at the back panel of the freezer, turn off the fridge for several hours to manually defrost it.
If the problem returns soon after, the defrost heater or thermostat likely needs replacement.

 

c. Refrigerator Runs Constantly

Possible causes:

Thermostat set too low.

Dirty coils or poor ventilation.

Door seals (gaskets) not sealing properly.

Warm ambient conditions or frequent door openings.

A worn or dirty gasket lets warm air in, making the compressor work harder. Check the seal by closing a piece of paper in the door. If it slides out easily, the gasket needs attention.

 

d. Water Leaking on the Floor

Possible causes:

Clogged defrost drain tube.

Cracked or overflowing drain pan.

Condensation from high humidity.

Fix:
Remove the lower back panel inside the fridge, locate the drain hole, and clear it with warm water or a pipe cleaner.

 

e. Excessive Frost or Ice Buildup

Possible causes:

Faulty defrost heater or timer.

Door not closing fully.

Frequent door openings in humid conditions.

Prevention:
Ensure door gaskets are tight and intact. Run a complete defrost cycle if the frost layer exceeds 5 mm.

 

f. Strange Noises

Possible causes:

Gurgling or hissing: normal sound of refrigerant flowing.

Clicking: compressor relay engaging/disengaging.

Rattling: loose condenser coils or items touching the back of the fridge.

Buzzing or grinding: failing fan or compressor bearing.

Tip:
If the noise comes from inside the freezer, check that the evaporator fan isn’t hitting ice or debris.

 

5. Maintenance and Longevity Tips

A refrigerator may run continuously for 10–20 years — but only if maintained well.

Here’s how to keep yours in top shape:

1. Clean condenser coils every six months.
2. Keep door gaskets clean with mild soap and water — sticky residues weaken the seal.
3. Check temperature settings:

Fridge: 2–5°C (36–41°F)

Freezer: around –18°C (0°F)

4. Don’t overload — proper air circulation is key.
5. Allow airflow behind and below the fridge — at least 5–10 cm clearance.
6. Defrost when necessary, even in semi-automatic models.
7. Power protection: Use a voltage stabilizer in areas with fluctuating power.

And of course, unplug and clean during long vacations — running an empty fridge wastes energy.

 

6. The Engineering Magic of Cooling

From an engineering standpoint, the refrigerator is a perfect demonstration of thermodynamics in everyday life.
It’s a closed-loop heat pump that uses pressure, phase change, and precise control to maintain a stable microclimate for food.

Modern advances such as inverter compressors, smart temperature sensors, and eco-friendly refrigerants like R600a (isobutane) have made fridges quieter, more efficient, and more sustainable.

It’s fascinating to realize that the same physical principles that cool your fridge also enable air conditioning, industrial chillers, and even cryogenics just at different scales and pressures.

 

Conclusion: Respect the Cool

Your refrigerator doesn’t just cool food, it silently moves heat, 24 hours a day, using one of the most efficient mechanical systems humans have designed.

By understanding how it works and knowing the common issues, you can catch small problems early, save on repairs, and keep your food fresh for years to come.

Next time you grab a cold drink, give a nod to the compressor quietly working away behind the scenes the unsung hero of your kitchen.

Have you ever fixed a fridge fault yourself or spotted one of these symptoms? Share your experience in the comments below, it might just save someone else’s dinner!