How To Test A Compressor With A Multimeter

Compressors are essential to many industrial machines, allowing them to function efficiently and without fail. But what would you do if something went wrong with the compressor? Often, a compressor will malfunction due to a lack of maintenance or an issue with its components; testing your compressor using a multimeter comes in handy. Testing your compressor regularly ensures that it’s working correctly, helping to prevent any further issues from occurring. This blog post discusses how you can quickly test a compressor with a multimeter for maximum accuracy and detail. We’ll go through each testing step and explain why it’s vital for the long-term success of your machine’s performance.

How To Test A Compressor With A Multimeter

Common symptoms of a bad compressor:

Unusual noises:

A bad compressor often makes a loud, grinding or buzzing noise when running.


Compressors leaking oil or fluids from the unit may indicate a bad compressor.

Poor cooling:

If your compressor is not cooling as it should, this could be a sign of an internal mechanical problem or a bad compressor motor.

High vibration levels:

Excessive vibrations can damage components and lead to the failure of the compressor over time.

Reduced air pressure:

If the air pressure from your compressor is lower than usual, this could mean a fault in the main piston or crankshaft assembly, which would require repair or replacement.

Electrical issues:

Issues such as circuit breakers tripping, sparks coming from the unit, and lights flickering on and off can all be signs of a faulty compressor motor.

High temperatures:

If your compressor runs at higher than usual operating temperatures, this could indicate a bad compressor motor or internal mechanical problem such as misaligned bearings.

Overheating motors:

Compressors that overheat quickly may indicate a bad compressor motor which needs to be replaced.

Excessive oil consumption:

If you notice more oil is needed to maintain the proper lubrication levels, this could mean an internal leak or wear, causing increased consumption.

Short cycling:

If your compressor is constantly starting and stopping or cannot reach its required pressure, this could mean the unit is not operating correctly and needs to be serviced.

This list contains common symptoms you can look for to identify a bad compressor. However, it is always best to consult an experienced professional if you suspect a problem with your compressor. A qualified technician can diagnose and repair any issues that may arise quickly and efficiently, ensuring your compressor will continue to provide reliable operations.


Testing a compressor with a digital multimeter is vital in troubleshooting and diagnosing air conditioning issues. This simple procedure can help identify problems in the compressor and pinpoint ways to resolve them. Here’s what you need to know about testing a compressor with a multimeter:

  • Before starting the test, check for burns and other physical damages on the compressor.
  • Examine the ground and energy at the AC compressor clutch to ensure power reaches it properly.
  • Test the power supply to the AC compressor clutch by connecting a multimeter set to its lowest voltage setting with two leads to your compressor – one red lead to the battery positive terminal and a black lead to the negative terminal. If there’s no reading on the meter, you have a broken connection or compromised wiring that needs repair and must be addressed immediately.
  • Check connectors between the pressure switch and AC compressor clutch for any loose connections or signs of corrosion that can prevent proper system operation.
  • Measure ohm resistance within the switches by connecting a multimeter set to its highest resistance (ohms) setting with two leads to your compressor – one red lead to the battery positive terminal and a black lead to the negative terminal. If the reading is not within acceptable levels, you may need to replace the switch immediately.

These simple steps will help ensure that your air conditioning system is working correctly and that any problems are identified quickly and corrected before they can cause further damage. Remember, proper maintenance and testing of your AC system can save time, money and headache in the long run!

Frequently Asked Questions:

How can I test a compressor with a multimeter?

When using a multimeter to test a compressor, the first step is to ensure that the power is turned off and that any necessary safety precautions are taken. The positive lead of the multimeter should then be connected to one side of the compressor’s terminal and the negative lead to the other. The multimeter will then display an Ohm reading, which can be used to determine whether or not the circuit is resistive.

What are some problems associated with using a multimeter for compressor testing?

One of the most common issues when using a multimeter for testing compressors is incorrect wiring or connection points being used. If the wrong terminal is used or a connection is made to an incorrect compressor point, this can lead to inaccurate readings. Additionally, ensuring that the multimeter is set to the correct range when testing and that any safety precautions are taken is vital.

What type of readings should I expect with a multimeter?

The ohm reading displayed by the multimeter should be consistent with the resistance ratings listed in your compressor’s manual. If there is no resistance at all (the multimeter displays 0 ohms), then this indicates a short circuit which usually means that there has been an internal failure within the compressor.

Can other tests be done with a multimeter for compressors?

Yes, other tests that can be completed with a multimeter include testing capacitors and checking the voltage output of compressors. For capacitors, the multimeter should be set to the ‘Capacitance’ setting and then connected across each terminal of the capacitor to measure its capacitance value. When testing voltage output, the multimeter should be set to the ‘Voltmeter’ setting and placed across both terminals to measure the AC Voltage output.

What type of precautions should I take when using a multimeter?

When using a multimeter, it is vital to take all safety precautions. This includes providing power is off before connecting any wires or components and ensuring that the multimeter is set to the correct range and that any exposed wires are insulated. Additionally, it’s essential to always disconnect power before making any adjustments or repairs.


Finally, using a multimeter to test a compressor can effectively identify any underlying issues and keep your compressor running smoothly. However, it is essential to note that this test should not be used in place of professional diagnosis or repair. Call a qualified technician who can assess the situation and make the necessary repairs or provide advice when in doubt. It will help you get the most out of your compressor and keep it running smoothly for years.

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