Refrigerator Compressor Running but Not Cooling

Refrigerator Compressor Running but Not Cooling

nicO and 5 contributors
Last updated on

The compressor is the heart of your fridge. Diagnosing compressor issues starts with listening to your refrigerator — when and where does the sound appear? A stethoscope may help to answer these questions. Pull your fridge away from the wall and listen.

Regular Maintenance

It's important to perform regular fridge maintenance before trying these fixes. Your appliance should last for at least 10-15 years before needing replacement, so keep it running well with these tips.

Safety Note: Power Down Fridge

Before removing and replacing or continuity testing electrical components, power down the fridge. This will prevent damage to the components and prevent you from being electrocuted. Still, some electrical components — like capacitors — will store their charge and should not be tampered with.

  • If the fridge is pulled away from the wall, or if the power switch is easily accessible, remove the plug.
  • Otherwise, find the fridge’s circuit breaker in your breaker box and turn the circuit off.
    • Verify your fridge has lost power by opening the doors and seeing if the fridge lights turn on.

Safety Note: Sharp Sheet Metal

When working underneath the fridge, consider wearing gloves to avoid cuts from the sharp sheet metal. The sheet metal is the thin structural metal components mount to. While wearing gloves may make working more challenging, it’s worth protecting yourself.

Reset Power

When refrigerators experience temporary power outages, they may enter a safe mode. The safe mode protects the fridge's internal components from electrical overload. You'll have to reset power to your fridge.

  • Unplug your refrigerator. If the plug is too hard to reach, switch the circuit breaker off.
  • Wait 5 minutes before returning power to the fridge.
  • Once power is back, open your freezer and push the light switch 3 times to trigger a cooling cycle.
  • Monitor temperature over the next 24 hours.

Causes

1

At the backside and bottom of your fridge are the condenser and its coils. Refrigerant passes through the coils which dissipates heat during the cooling cycle. As dust and debris pile onto the coils, the fridge becomes less efficient and the compressor must work harder to cool down. In some cases, the compressor may be running constantly in an attempt to cool the fridge.

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  • Pull your fridge out and inspect the coils.
    • Your fridge may have an anti-tip bracket and can only be removed by pulling straight out from the wall.
  • Clean dust off condenser coils and fan with a stiff brush and vacuum.
  • Work carefully during this task and avoid bending or damaging the tubes.
2

The condenser fan draws air over the compressor and through the condenser coils. If the fan motor isn't working normally, then the fridge won't cool properly. It's normally located at the bottom of the fridge and blows air onto the condenser coils.

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The evaporator fan draws air over the cooling coils and circulates this air within the fridge and freezer compartments. The evaporator fan should be running as long as the compressor motor is running. If your fridge only has one evaporator fan motor, it's located in the freezer compartment. When the fan fails, it won't circulate the cold air to the refrigerator. In this event, the freezer may still get cold while the refrigerator stays warm.

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3

If the evaporator cover in your freezer is covered in ice crystals, or otherwise frozen over, there's an issue with your defrost system.

Defrost Type

Frost-free appliances regulate temperature to prevent ice build-up. Automatic and adaptive defrost systems prevent and remove ice build-up by circulating heat as needed; automatic systems typically run on a timer, while adaptive systems use sensors to determine when to circulate the heat.

4

The most modern freezers have an auto-defrost system. This defrost system has four main parts: a defrost heater, a bi-metal thermostat, an electronic control board, and a thermistor. Let's begin troubleshooting the defrost heater system.

  • Test to see if the defrost heater works. Put your freezer into forced defrost mode. On some models this mode is entered by pushing the door sensor 5 times in 2 seconds. The controller will beep and the defrost mode will start. This mode can be exited by unplugging the fridge.
    • If this procedure doesn't work, check the tech sheet located under or behind your fridge for your specific procedures.
  • Check to see if the heater heats up.
    • If it heats up, jump to the thermistor section.
    • If it doesn't heat up, begin troubleshooting the system starting with the defrost heater.
5

Like a breaker tripping under a power load, your thermal fuse may trip and blow when your appliance overheats. One sign that your fuse may have blown is your evaporator freezing over.

  • Continuity test your fuse and replace it if the reading is more than 1Ω
6

The defrost heater melts frost off evaporator fins. If the defrost heater fails, the frost stays put and the entire refrigerator eventually becomes ice.

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  • Locate the defrost heater. If you notice any bumps or cracks, replace immediately.
  • Continuity test the heater. A resistance value outside 50-120Ω will need to be replaced with a new unit.
7

The defrost timer is in charge of initiating 30 minute heating cycles every 10 hours of fridge run time. If this unit fails, your fridge will be stuck in either the heating or cooling cycle. It's time to test the defrost timer.

  • In units with an adaptive defrost control board, you'll have to manually enable the defrost cycle.
    • Turn the thermostat off for 15 seconds, then on for 5 seconds. Repeat this two more times, then turn the thermostat off.
    • Defrost cycle should be turned on. Test temperature with a thermometer to see if your fridge is heating up.
  • With a manual timer, test between terminals 1 and 4 for continuity.
    • Continuity here means that the cooling cycle is operating.
  • Rotate the manual dial until hearing a click. Now test between pins 1 and 2 for continuity. This means that the heating cycle is working, and there should be no continuity between pins 1 and 4.
  • Replace timer with a new one if continuity tests fail, or fridge doesn't enter defrost mode.
8

If the refrigerator still does not get cold enough, the temperature control thermostat (also called bi-metal thermostat) might be faulty. The thermostat allows power to flow through to the compressor, evaporator fan, and condenser fan. If the cooling system fans and compressor are running, but the refrigerator or freezer is not cooling correctly, check for an airflow or defrost system problem.

9

Another problem that prevents your fridge from getting cold enough is a faulty thermistor. The thermistor is a sensor which monitors the air temperature. It is connected to the control board. If the thermistor is defective, the refrigerator does not cool (or may cool continuously).

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  • Grab a multimeter and continuity test the thermistor or if you need to pick up a new one pick up a new one. You can measure the thermistor if it is 46 degrees Fahrenheit (7 degrees Celsius) or colder. Place the thermistor tip into a cup of ice water and cool if you're above target temperature.
  • If the value isn't between 10—15kΩ, replace your temperature sensor with a new thermistor.
10

If the refrigerator is not cold enough, the temperature control board might be defective. The temperature control board provides voltage to the fan motors and compressor. The electronic control board starts the defrost cycle and regulates how often they are triggered. If the control fails, your fridge will not be able to defrost automatically.

  • These boards are often misdiagnosed. Check all other components to be certain this is the cause of the problem.
11

Sometimes if the refrigerator isn't cold enough, the compressor might be having difficulty starting up. The start capacitor serves as a battery to give the compressor a boost of power during startup. If the start capacitor is burned out —and smells burnt — the compressor might not be able to start and run as often as it should.

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  • Safely remove the capacitor and discharge with a discharge tool.
    • On smaller capacitors, you can use a screwdriver to discharge. But be careful as capacitors increase in size.
  • Test the start capacitor first with a capacitance meter; they don't fail often. If it's faulty, replace it.
12

The overload relay is a protection device in the compressor circuit and is often combined with the start relay. You can find it plugged directly into the side of the compressor. If the fans are running and your compressor won’t start, or if you hear a clicking sound from the unit follow troubleshooting below.

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  • Check the overload relay for signs of overheating or arcing.
    • This may be a hot module, burnt, or rattles when shaken.
  • Check for continuity with a multimeter.
13

The start relay is a small device mounted to the side of the compressor. It provides power to the run winding, along with the start winding, for a split second at startup to help get the compressor going. If the start relay is defective, the compressor may run intermittently or not at all, and the refrigerator will not get cold enough. The start relay should be replaced if defective.

  • Test Start Relay with a multimeter. View the video above and verify if your start relay is functioning.
  • Replace relay if it fails the testing or has a burnt odor. Depending on your start relay, you may have to test the start capacitor and overload relay first and use a process of elimination. If the other two components pass continuity tests, and your compressor isn't starting, try replacing your start relay.
14

The compressor — also called the condenser — is the workhorse of your fridge. By pressurizing the refrigerant, the evaporator is able to create cold air. If the compressor is very noisy when you start it up, it may have been damaged in transit, or you could just have a faulty compressor.

If the overload relay, start relay and start capacitor pass continuity testing, then you may have a defective compressor.

  • Test the compressor for continuity by following the video above.
  • Resistance values vary based on compressor.
  • Values outside of the range or a short to ground will mean replacing the compressor with a new one, which is a costly repair.
  • If your fridge is more than a few years old, you may be better off replacing the fridge instead of the compressor.
15

Modern refrigerator compressor technology has shifted from single phase DC motors to 3-phase DC-controlled AC motors.

What this means is that instead of the start relay assembly normally attached to the compressor pins — the start relay, overload relay, and overload capacitor — there is now a sealed motherboard and a lot of wires. The inverter board modulates the power supplied to the compressor and allows for more efficient operation.

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This new technology is harder to test, so this video may be helpful.

The inverter board must be tested by process of elimination.

  • First, test the input voltages. The inverter board will have both a 120V AC main power supply voltage, and a 4-6V DC voltage from the main control board. Remember to make all voltage measurements with everything connected.
  • If one of these voltages is missing, the inverter board will not work.
    • Backtrack to find the issue. You could have a faulty wire harness connector, a bad motherboard, or another issue.
  • Second, follow the compressor continuity testing from above to verify your compressor isn't shorted and is okay.
    • If the compressor is fine, and the board input voltages are fine, then your inverter board has failed and needs replacing.
16

If there is a refrigerant leak, the fridge won't be able to maintain a proper temperature. Your compressor is likely running non-stop.

  • Contact a service technician to inspect your compressor.
  • This may result in refilling or replacing your refrigerant, or replacing the entire fridge.
17

Finally, if the refrigerator won’t get cold enough, the main control board might be defective. This is not common.

  • Check and test the defrost system, cooling fans, and cooling controls first.
  • If none of the other components are defective, consider replacing the main control board.

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