Testing A Refrigerator Compressor For Incoming Voltage

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You’ve started to notice that the gallon of milk you put in the refrigerator a few days ago is going sour and now the meat in the freezer compartment is definitely starting to defrost. There’s no doubt about it: your refrigerator has a cooling problem. Your first troubleshooting step is to confirm the refrigerator is periodically going through its defrost cycle (make sure there’s no ice buildup on the evaporator coils). Next, check to see if the appliance’s evaporator fan motor or motors are functioning.

Okay, so the defrost system and fan motors seem to be working fine; what’s next? If you haven’t heard the refrigerator cycle on in a while the compressor’s start relay may be malfunctioning or the compressor itself could be defective. Replacing a faulty compressor is a major repair, so before you consider that action you should confirm the compressor is receiving the incoming power it needs to operate. In this article, Repair Clinic will walk you through testing the refrigerator’s compressor for incoming voltage, but let’s review how the compressor keeps the refrigerator cold first.

How the compressor keeps a refrigerator cold

While we may think of a refrigerator as an appliance that creates coldness, it’s more accurate to say that the refrigeration system removes the heat from the air traveling through the refrigerator and freezer compartments. The more heat and humidity that is removed, the colder those compartments will be.

The compressor compresses refrigerant in gas form into the condenser coils

To accomplish this, a refrigerator uses a compressor to pump refrigerant through a set of coils, and fan motors to circulate the air. The compressor compresses the refrigerant in gas form into the condenser coils (often located at the bottom of the appliance) where the gas is then condensed into a hot liquid. The condenser coils dissipate the heat as the liquid travels through them.

The refrigerant in the evaporator coils expands back into a gas

When the refrigerant reaches the evaporator coils (usually located behind a rear panel in the freezer compartment, although some models will place these coils behind a rear panel in the refrigerator compartment), it expands back into a gas which makes the coils cold. The gas continues to flow through a suction line attached to the compressor which compresses the gas back into the condenser coils (which condenses the gas back into a hot liquid) and the cooling cycle repeats.

The compressor and fan motors run occasionally throughout the day

A condenser fan motor assists the condenser coils in dissipating the heat while an evaporator fan motor draws air over the cold evaporator coils and then circulates that air through the refrigerator and freezer compartments. The compressor and fan motor only have to run occasionally throughout the day to maintain the appropriate temperature in the refrigerator.

What is an appropriate temperature for the refrigerator?

What is an appropriate temperature for the refrigerator? Around 40° Fahrenheit (4° Celsius) in the refrigerator compartment and 0° Fahrenheit (-18° Celsius) in the freezer compartment. A significantly higher temperature indicates a failure somewhere in the refrigeration system.

Where is the compressor located?

While the compressor can be found at the top of the appliance for built-in refrigerators (these are refrigerators that are seated in a recessed space surrounded by cabinets), nearly all models have the compressor located at the bottom rear of the appliance behind an access panel. You will need to pull the refrigerator away from the wall and unthread the screws to remove the access panel to reach the compressor.

Not all refrigerator compressors can be tested for incoming voltage

Not all refrigerator models allow you to test for incoming voltage. Some more recent models will automatically shut off the power to the compressor if the power input wire connector has been disconnected; this will prevent you from testing for incoming power. However, if the control board allows voltage to travel through the disconnected power input wires, you can conduct the test to determine what’s preventing the compressor from cycling on.

How to test a refrigerator compressor for incoming voltage in 8 steps

You will need a multimeter to test the refrigerator compressor for incoming voltage. With a meter at the ready, here are the 8 steps you can follow to conduct the test:

  • 1) Unplug the power cord – Before you begin any disassembly, unplug the refrigerator’s power cord to avoid a potential electric shock.
  • 2) Access the compressor – To reach the compressor you will need to pull the refrigerator away from the wall and unthread the screws to remove the lower access panel. Be aware, you may need to detach a water inlet line in order to fully remove the panel.
  • 3) Disconnect the compressor wire connector – Disconnect the compressor’s incoming power connector or wires.
  • 4) Identify the compressor’s voltage designation – Your next step is to identify the compressor’s voltage designation. You can usually find this information in the refrigerator’s tech sheet or it may be printed on a label attached to the compressor (Example: “115 – 127V, 60 Hz”).
  • 5) Set the multimeter – Rotate the multimeter’s range selection dial to “Volts AC” or “Volts DC” as required to match the compressor’s voltage designation.
  • 6) Plug the power cord back in – Next, plug the power cord back into the electrical outlet. Since the refrigerator now has power again, avoid touching any electrical components with your bare hands.
  • 7) Contact the meter leads to the power input connector – Contact the black meter lead to one of the power input connector pins or wires and the red meter lead to the other pin or wire.
  • 8) Observe the meter display – With the meter leads touching the power input connector pins or wires the meter display should indicate that voltage is present, although you may need to wait a few minutes for the control board to send power to the compressor circuit in order to see a reading. Be aware that some compressors use variable voltage so the reading may change during the testing. If the meter display indicates that power is reaching the compressor, then the start relay or the compressor itself could be responsible for the cooling problem. However, if the meter display indicates that no voltage is present, then the refrigerator’s main control board or invertor board is likely defective and will need to be replaced.
Refrigerator Compressor Voltage Testing

Genuine OEM refrigerator parts are a must

Has the voltage testing revealed that you need to install a new start relay, control board, or invertor board? Know that your repair will be much more successful if you use a genuine OEM replacement part. Genuine manufacturer parts, such as those from KitchenAid, GE, Kenmore, LG, Samsung, Frigidaire, Maytag, or Whirlpool, are designed to work with specific refrigerator models and can last longer than generic parts. To find the exact OEM part you need, enter the full model number of the refrigerator in the Repair Clinic search bar to see a complete list of compatible parts. You can then use the “Part Category” (example: “Circuit Board & Timer”) and “Part Title” (example: “Inverter Board”) navigation filters to refine the list to locate the specific part you’re looking for.

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