How to Test a Fan Motor With a Multimeter

How to Test a Fan Motor With a Multimeter

It can sometimes be very confusing to test fan motors for people who don’t have much experience. This guide will hopefully make testing fan motors for you easy, regardless of your experience level or type of fan motor that you are testing.

As you probably know, fan motors can be designed for several different purposes. Most common of these are single phase motors. Other types of fan motors, like split phase and capacitor start motors, are intended for industrial environments and they are very common in factories and warehouses. 

The advice mentioned here applies to every four-wire configuration fan motor, regardless of fan motor size.

Note: In this test, we use one of my favorite multimeter -- Fluke 117 

Wire configuration

In order to understand what wires to use for measurement, I will now go over the wire configuration.

Fan motors usually have two wires; brown and white – brown wires that are plugged into the capacitor. Other two wires are black and white and they are to be plugged into the capacitor. We will test the wires according to their functions.

!! Before you start testing, make sure that the power is off on the fan motor !!
fan wire configuration

Number one cause of fan motor problems

One more thing before you start testing.

The top cause of fan motor ‘breakdowns’ is a bad run capacitor. Always visually check the capacitor before you start testing because ruptured capacitors and capacitors with dents or any other types of deformities are obviously broken and you need to replace them as soon as possible. 

It goes without saying that everything is probably fine with the fan motor if you detect such a capacitor. I would, however, proceed with the tests just to make sure that there isn’t something wrong with the fan motor because, if it is, it could make the new capacitor break down.

How to Test a Fan Motor With a Multimeter

Test the first set of wires:

Now is the time to test the white – brown and white wires. The white wire is called the run wire.

multimeter for household
  • Take your multimeter and set it to ohms. 
  • Take the black multimeter standard test lead and touch the white wire with it.
  • Touch and continue touching the white – brown wire with the red multimeter probe.

Values measured in this step should be around point one or point two ohms.

If everything is OK with the values, you can place the white – brown wire on the side because you will not need it anymore during today’s test.

Test the second set of wires:

The brown wire is the start wire and the black wire is the common wire.

  • Take your multimeter and place the negative (black) multimeter probe on the brown wire.
  • You should put the red probe on the white wire.

Any value between and around thirty-two to forty ohms should be considered as standard value. 

Test the third set of wires:

  • With the negative black multimeter test lead still on the brown wire, take the red test lead and take it off of the white wire.
  • You will now place the red probe on the common wire.

Values measured in this phase of testing should be around fifteen ohms.

Test the fourth set of wires:

  • Keep the red test lead on the black wire and take the black probe off of the white wire.
  • Place the black probe on the white wire.
  • It is preferable to do this test without the moving blade.

The multimeter should show values around twenty ohms.

Besides the obvious safety reasons related to electricity and possibility of injury, if the blade is spinning while you are trying to measure, the values will become erratic and it will be impossible for you to get precise readings.


South-wire clips are excellent for this kind of job.

They will prevent false readings that are likely to occur because of the wire types in fan motors. Rubber around south-wires will keep the wire strings inside.

Here is the list of succinct wire names according to their function:

  • The white wire is called the run wire, the brown wire is called the start wire and the black wire is called the common wire.
  • If your fan motor differs in any way to the configuration described here make sure to get the manual and check it for details.
  • If you are still unable to locate or identify a part necessary for testing described here, make sure to check out the metallic plate on the fan motor. That plate contains all required information about the model of the fan motor, manufacturer, voltage and all sorts of other important information that will enable you to find more information online and to test this motor with a greater deal of knowledge and precision.

Although it was confusing at first, the steps in this process helped me to test my fan motor, correctly diagnose the problem and repair it.

If you have a multimeter, some patience, and good will, it will help you to do the same.

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