How to Check Vacuum Motor Brushes With a Multimeter

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The person typing how to check a vacuum cleaner motor brushes with a multimeter wants to know whether worn brushes are the reason the vacuum has lost power, sparks, or stopped running. A multimeter can check whether the brush circuit is open, and it can check the winding that the brushes feed. It cannot measure how much carbon is left on a brush, and it cannot show whether the commutator is scored. This guide covers the unplug steps, the continuity and resistance checks, and where a meter check stops and a visual inspection has to take over.

Quick answer

Unplug the vacuum and let the motor stop before you open the housing.
Use continuity mode with the power off to check whether the brush lead and its connection are complete.
Use resistance mode on the motor winding with the motor disconnected. An open winding reads OL, and a shorted winding reads near 0 Ω.
A meter cannot measure brush length. Look at the brushes directly, and compare them with the service data for your model.
The sources opened for this guide do not give a brush wear limit for any vacuum, so do not replace a brush based on a meter reading alone.

Safety first

A vacuum motor is powered from household mains. Unplug the vacuum, then wait for the motor to stop before you touch the motor area. Fluke’s general guidance on multimeter use says to turn off circuit power and discharge any high-voltage capacitor before you test resistance, continuity, diodes or capacitance. Fluke also says to disconnect the test leads before opening the meter’s case or battery door.

Do not run a vacuum with its brush cover off, and do not reach into the motor area while the cord is connected. If you see burn marks on the commutator, smell burning, or find a cracked brush holder, stop and have the unit serviced by a qualified repair shop.

What you need

A digital multimeter with continuity mode and an ohms range. Fluke notes that continuity is often on the same dial position as resistance, so check the dial before each test.
A screwdriver set that matches the screws on the motor housing and the brush cover.
A way to label each lead before you disconnect it, such as a photo or a piece of tape.
A bright light and a clean cloth, so you can see the brushes and the commutator without touching the moving parts.
The model number, so you can check the brush wiring and any wear limit in the service data.

Step 1: Find the brush holders and the leads

Open the motor cover with the vacuum unplugged, and find the brush holders. A motor with brushes has a brush holder and a lead for each brush, and each lead runs to the motor winding through a terminal. Note the position of each brush and each lead before you disconnect anything, because reconnecting a lead to the wrong terminal can damage the motor. The sources opened for this guide do not describe vacuum motor layouts, so the service data for your model decides how many brushes and leads there are.

Do not remove a brush from its holder until you have checked its spring and holder. Some holders are fragile, and a loose spring can send a brush into the commutator.

Step 2: Check the brush lead with continuity mode

With the vacuum unplugged, set the meter to continuity mode. Fluke’s continuity guide says to turn the dial to the continuity test mode, and to press the continuity button if your model has one. Confirm that the meter beeps when the leads touch, and then connect the leads across the brush lead and its terminal. Fluke says the position of the leads is arbitrary, but the part under test should be isolated from other components.

A beep means the brush lead has a complete path. No beep means the path is open, which can point to a broken lead, a loose terminal or a brush that has worn so short that its pigtail no longer reaches the spring. Before you condemn the brush, clean the terminal and reseat the lead, then test again. A brush that beeps may still make poor contact with the commutator, because continuity checks only the lead and the path, not the pressure on the brush.

Step 3: Check the motor winding with resistance mode

With the motor leads disconnected from the switch and the brushes, set the meter to resistance. Fluke’s 116 HVAC guidance gives the result for a motor winding. An open winding reads OL. A shorted winding reads near 0 Ω. The guidance also says that if the windings are open or shorted, they should be replaced. The sources do not say which terminals to measure on a vacuum motor, so use the model’s wiring diagram to pick the right pairs.

Fluke’s resistance guide notes that the reading can be affected by parallel paths. If the motor is still wired to other parts, the reading may not show the winding alone. Disconnect the motor from the circuit where you can, and compare the reading with the service data if it is available.

Step 4: Look at the brushes and the commutator

A meter cannot show how worn a brush is. Look at the brush carbon with a light. If the carbon is very short, cracked, chipped, or stuck in its holder, the brush needs a closer look or a replacement. Look at the commutator too. A commutator with grooves, burn marks or a dark, uneven surface can cause sparking even when the brush circuit reads correctly.

Turn the motor by hand only when it is disconnected and the brushes are clear of the commutator. Feel for rough spots, and look for a brush that moves freely in its holder. These checks do not give a number, but they can explain a fault that the meter cannot find.

Step 5: Decide what the readings mean together

An open brush lead with a good winding points to the brush circuit. An open winding points to the motor. A shorted winding points to the motor as well. A brush that beeps, a winding with a normal reading, and a clean commutator do not prove the vacuum is healthy, because the meter cannot see the brush pressure, the bearing condition or the speed of the motor under load.

Write down each reading with its terminal pair. A comparison between the two brush leads and between the two halves of the winding is more useful than a single number you cannot compare.

Common mistakes

Testing while the vacuum is plugged in. Fluke’s guidance is to turn off circuit power before continuity or resistance tests.
Treating a beep as proof that the brush contacts the commutator well.
Replacing brushes without checking the terminals, the springs and the holders.
Measuring a motor winding in circuit and reading the result as a winding value. Parallel paths can change the reading.
Reconnecting leads to the wrong terminals after the brushes have been removed.

How we chose

This guide uses three Fluke Learn pages that we opened on 2026-10-27. We chose the continuity step for the brush leads, the resistance step for the winding, and the safety steps from Fluke’s general guide. We did not find a Fluke page that covers vacuum motor brushes, so the brush wear part of this guide is a visual check, and the meter’s role is limited to the electrical path.

What we could not verify

A brush wear limit for any vacuum. The sources opened do not give a minimum brush length.
The number of brushes, the lead layout and the winding terminals inside a particular vacuum.
The resistance of a healthy vacuum motor winding. No figure in the sources applies to vacuum motors.
Whether a meter check finds a commutator fault, a stuck brush or a worn bearing.
Whether a brush replacement with a different part number changes the motor’s performance.

FAQ

Can a multimeter measure how worn a brush is?

No. A meter can check whether the brush lead is complete, but it does not measure the length of the carbon. Check the brush against the service data for your model, and look at it directly.

What does a beep on a brush lead tell me?

It means the lead and its path are complete at the moment of the test. It does not show that the brush presses firmly on the commutator, and it does not show that the brush has enough carbon left.

Why does the motor winding read OL?

Fluke’s HVAC guidance says an open winding reads OL in resistance mode. Check that the leads are on the correct terminals and that the meter is in the right mode. If the reading is still OL, the winding is the likely fault, and the motor needs service.

Should I replace both brushes together?

The sources opened for this guide do not say whether brushes should be replaced in pairs. Follow the service data for your model, and check the springs and holders before you fit new brushes.

Is it safe to do this myself?

The checks with the power off are simple, but the motor sits inside a mains-powered appliance. Stop if you see burn marks, a cracked brush holder or any sign of arcing, and ask a qualified repair shop to look at the unit.

Bottom line

Unplug the vacuum, check the brush leads for continuity, and check the winding in resistance mode with the motor disconnected. Then look at the brushes and the commutator directly. A meter can rule out an open lead or a short in the winding, but the sources give no wear limit, so brush replacement should follow the model’s service data and a visual check.

Sources

Fluke, “A Guide to Continuity Testing with a Multimeter”, https://www.fluke.com/en-us/learn/blog/digital-multimeters/how-to-test-for-continuity, opened 2026-10-27.
Fluke, “Troubleshooting 10 Common Issues with the Fluke 116 HVAC Multimeter”, https://www.fluke.com/en-us/learn/blog/hvac/troubleshooting-10-common-issues-with-the-fluke-116-hvac-multimeter, opened 2026-10-27.
Fluke, “How to Use a Multimeter: A Comprehensive Guide”, https://www.fluke.com/en-us/learn/blog/maintenance-monitoring/how-to-use-a-multimeter-guide, opened 2026-10-27.