How the Compressor Works in a Refrigerator

Your refrigerator hums along quietly in the background every day, and you probably don’t think much about what’s actually making it cold, until it stops. That steady hum you hear? That’s the compressor, and it’s doing the heavy lifting behind every degree of cooling in both your freezer and fridge compartments. Understanding how it works puts you in a much better position to diagnose problems early, before you’re left scrambling to keep food fresh during a breakdown.

Whether you own a Whirlpool, Frigidaire, GE, Samsung, LG, or any other major brand, the compressor operates on the same fundamental principles. The details here apply across the board.

How to Tell If Your Compressor Is the Problem

Before we get into how the compressor work, let’s cover what you actually came here for, figuring out whether yours is failing. We see people replace expensive compressors when the real culprit was a start relay or a dirty set of condenser coils. So let’s rule out the easy stuff first.

The Refrigerator Isn’t Cooling at All

1. Open the door and check whether the interior light comes on. If it does, you have power to the unit.
2. Listen carefully near the back or bottom of the fridge. You should hear either the compressor humming or the fans running. If you hear absolutely nothing, no fan, no hum, locate the wiring diagram (usually taped inside the unit or behind the kickplate) and verify you have 120 volts AC reaching the control board.
3. If the fans are running but the compressor isn’t, the issue is likely a bad start device (the relay and overload attached directly to the compressor) or the compressor itself. Unplug the refrigerator before touching anything. Pull the start relay off the compressor terminals, it’s a small box that plugs right onto the side or back of the compressor. Shake it gently. If it rattles, the relay is burned out and needs replacing. That’s a common, inexpensive fix.
4. If the start relay seems fine and the compressor still won’t kick on, you may have a failed compressor or a control board issue. Check for voltage at the compressor terminals with a multimeter set to AC volts. If you’re reading 120V there and the compressor won’t start, the compressor is likely shot.

The Compressor Runs but the Fridge Is Warm

This is the scenario we deal with constantly. The compressor is humming away, but temperatures keep climbing.

1. Pull the refrigerator away from the wall and check the condenser coils. On most models, they’re either on the back of the unit or underneath behind the front kickplate. If they’re caked with dust, pet hair, or grease, clean them thoroughly with a coil brush and vacuum. Dirty coils force the compressor to run overtime and can prevent the fridge from reaching temperature. After cleaning, give the unit a full 24 hours to stabilize.
2. If the coils are clean and the compressor runs nonstop, open the freezer and check the evaporator coils (behind the interior back panel of the freezer). Unplug the fridge first. Remove the screws holding the panel in place and look at the frost pattern. A fully frosted evaporator that’s evenly covered means the sealed system is working, your problem is likely a defrost issue, not the compressor. A partially frosted evaporator with frost on only the first few passes of tubing usually points to a sealed system problem like a refrigerant leak or a failing compressor.
3. Verify the evaporator fan is running when the door is closed (press the door switch manually). If fans and compressor are both running, coils are clean, and the evaporator has a partial frost pattern, you’re looking at a sealed system issue that involves the compressor circuit.

If you’re stuck mid-diagnosis, post your model number and what you’re seeing on the community repair forum, you’ll get experienced eyes on it fast.

What the Compressor Actually Does

Now that you know how to spot trouble, here’s why the compressor matters so much.

Your refrigerator doesn’t create cold. It removes heat. The compressor is the engine that drives this process by circulating refrigerant, a chemical that changes between liquid and gas, through a closed loop of tubing.

Here’s the cycle in plain terms:

1. Compression. The compressor takes low-pressure refrigerant gas from the evaporator (inside the freezer) and squeezes it into a high-pressure, high-temperature gas. This is the work that creates the humming sound you hear.
2. Condensation. That hot, pressurized gas flows into the condenser coils (usually at the back or bottom of the fridge). As air passes over the coils, the gas releases its heat into the room and condenses into a high-pressure liquid. This is why the area around your condenser coils feels warm, that’s the heat being pulled out of your food.
3. Expansion. The liquid refrigerant passes through a tiny restriction called a capillary tube (a very narrow section of copper tubing). This sudden drop in pressure causes the refrigerant’s temperature to plummet.
4. Evaporation. The now-cold, low-pressure refrigerant enters the evaporator coils inside the freezer compartment. It absorbs heat from the air inside the fridge, which is what actually makes things cold. The refrigerant boils back into a gas as it absorbs that heat, and then it flows back to the compressor to start the cycle again.

The compressor is essentially a small electric motor driving a piston or scroll mechanism sealed inside a steel housing. It’s hermetically sealed, meaning you can’t open it or service the internals. When a compressor fails mechanically, the whole unit gets replaced.

Why Compressors Fail

Compressors are built to last 10 to 20 years, but certain conditions shorten that lifespan dramatically. Dirty condenser coils are the number one killer, they force the compressor to work harder and run hotter than it was designed to. Electrical problems like voltage spikes or a failing start relay can also burn out the motor windings over time. And restricted airflow from pushing the fridge too close to the wall traps heat around the condenser, adding unnecessary strain.

If your compressor is running constantly but temperatures are still off, start with the basics: clean the coils, check the start relay, and inspect the evaporator frost pattern. You can find replacement refrigerator parts, including start relays, thermistors, and fan motors, by searching your model number on our repair help page.

How to Know Everything’s Working Properly

After any troubleshooting or repair, verify the fix by placing a thermometer in both the freezer and the refrigerator compartment. The freezer should hold between 0°F and 5°F, and the fridge should sit between 35°F and 38°F. Give the unit a full 24 hours after any change before judging the results, refrigerators stabilize slowly.

Listen for the compressor cycling on and off normally. A healthy compressor runs for a while, shuts off when temperatures are reached, then kicks back on as things warm up. If it runs without ever cycling off, something is still wrong.

Where To Find Us 

If you need any replacement parts for your appliances, you can enter your model number at AppliancePartsPros.com to locate and order them quickly. Most orders arrive in just two business days, and we have tons of great information in our repair help section and YouTube videos to help you troubleshoot.

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FAQ

How long should a refrigerator compressor run before shutting off?

It depends on the ambient temperature and how often the doors are opened, but most compressors run for 30 to 60 minutes, then cycle off for a similar period. In a hot kitchen or after loading warm groceries, longer run times are normal. If it runs 24/7 without stopping, check your condenser coils and evaporator frost pattern.

Can I replace a refrigerator compressor myself?

Technically, removing and installing the compressor is straightforward mechanical work. However, recharging the sealed system with refrigerant requires EPA Section 608 certification and specialized recovery equipment. Refrigerant handling is regulated.

What does a bad compressor sound like?

A failing compressor often clicks on, hums loudly for a few seconds, then clicks off, repeating this cycle every few minutes. That’s the overload protector cutting power because the compressor can’t start. You might also hear a loud buzzing or knocking sound. Before blaming the compressor, pull off the start relay and shake it, a rattling relay causes the exact same symptom and costs a fraction of what a compressor does.

Why is my refrigerator compressor hot to the touch?

Some warmth is completely normal, compressors generate heat as part of the refrigeration cycle. But if it’s too hot to keep your hand on for more than a second or two, that’s excessive. Check for dirty condenser coils, poor ventilation behind the fridge, or an overcharged system. Sustained overheating will eventually kill the compressor.