How do you know if your refrigerator compressor is bad?

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The compressor is the heart of any refrigerator. This is the motor at the back of the fridge that is responsible for circulating the refrigerant in the fridge. When it is not working, the fridge does not cool or freeze things like it should with the thermostat set correctly. Therefore, one of the signs that the refrigerator compressor is bad or needs your attention is when it runs without cooling. You can tell this if ice starts to melt and won’t form or if the fridge compartment get’s a little warmer. Food going bad in the fridge is also an indicator that something is wrong.

Before you call an HVAC guy to come and fix your fridge, it is good to troubleshoot it yourself to find out what could be wrong. It is also good to not be clueless about what needs to be fixed. But if you are a handy guy like me, you can even attempt to fix some of the small problems and save some money. In this post, I show you how to test the compressor of your refrigerator so you can tell when it is time to refill, replace, or get a new fridge altogether.

Why would you want to test the refrigerator compressor?

As I have mentioned, the refrigerator compressor is the heart of any fridge. So when it is not working properly, you don’t have a refrigerator. Some of the reasons you would want to test it are if it is running without cooling, overheating, or not running at all.

How to test the fridge compressor

testing the compressor of a refrigerator with DMM
Testing fridge compressor

Tools needed:

  • Digital multimeter
  • Phillips screwdriver

Instructions

Step 1: Unplug the power cord from the wall outlet.

Step 2: Pull the refrigerator from the wall to access the back side. You can even turn it around to get good access to the backside.

Step 3: Use a screwdriver to remove the back cover or water tray (for small fridges) to access the compressor. The compressor is the metallic cylinder you see at the back of the fridge. Remove anything else that may prevent you from accessing it.

Step 4: Unscrew the set screw on the relay cover to access the relay assembly. This is where the electrical cords terminate on the side of the compressor.

Step 5: Pull the relay assembly from the compressor. If it is hard, use a flat screwdriver to pry it out gently to avoid breaking or bending the prongs.

Step 6: Once the relay assembly is out, you will see three prongs sticking out of the compressor. Those are what provide electrical connection to the windings of the motor in the compressor.

The prongs are arranged in a triangular manner. Either one on the top and two at the bottom or vise versa. The single prong at the top or bottom is the common pin and the other two connect to the starter coil and main/run coil respectively.

Step 7: Test the compressor windings with the digital multimeter. Here is how to do it:

How to troubleshoot a refrigerator compressor with a digital multimeter

  1. Plug the black probe or jack into the port labeled “COMMON” and the red one to the port labeled “V/Ω” on your multimeter.
  2. Set your multimeter to measure resistance or ohms
  3. Measure the resistance of the starter coil by connecting the black probe tip to the common prong and the red probe to the starter winding prong on the compressor.
  4. Measure the resistance of the main/run coil by connecting the black probe tip to the common prong and the red prove to the Main/Run winding prong on the compressor.
  5. Determine the resistance of both the Main/primary and starter/secondary coil by connecting one probe to the starter coil prong and the other probe to the Main/Run winding pin.
  6. Measure the resistance between the compressor windings and ground by connecting one probe to the body of the compressor and the other to each of the two motor winding probes. You might have to scratch a little bit with the probe to expose the metallic surface if your compressor is coated.
  7. Note down the measurements.

Step 8: Compare the measurements with the manufacturer’s values. You can get the values from the compressor repair manual which you can easily find by searching its serial number online.

Step 9: Interpret the readings. The table below is a summary of what to make about the resistance measurements.

How to interpret the readings

MeasurementPurposeInterpretation
Between Starter pin and commonMeasures the resistance of the starter windingshould be within 5% of the manufacturer’s value
Between Main/Run pin and commonMeasures the resistance of the main windingshould be within 5% of the manufacturer’s value
Between main and starter pinsMeasures the resistance of both the starter and main windingshould be a sum of the top 2 values
Between main pin and compressor casingDetermines the resistance between main winding and groundShould be an open circuit or (OL)
Between starter pin and compressor casingMeasures the resistance between starter winding and groundShould be open circuit or (OL)

If the values are not within 5% of what is in the repair manual, then you know your refrigerator compressor is starting to give in. Furthermore, if there is continuity between the windings and the casing, then the motor is shorted and you should replace it.

If the values are correct and the compressor is running but not cooling, it is time to refill with Freon. Contact a HVAC guy to come and refill it for you.

Lastly, if the values are correct but the compressor is not running, then the relay or the main power supply to the compressor has a problem. You can try to test the compressor without the relay assembly just to be sure it is ok.

Well, that how to troubleshoot a refrigerator compressor with a digital multimeter when it not working properly.

How to test the compressor of your refrigerator using a multimeter (Video)

Julius

Julius an engineer. Throughout his career, he has encountered many tools and learned that getting the right tools for the trade is key to getting the job done right. That is why he talks about tools.