Skip to content
Shop Products

Troubleshoot Central Vacuum Motor, Relay, Transformer, Motor Brushes

Need to test or troubleshoot a vacuum motor or even a relay or circuit brush? You'll find the steps you need here.

We recommend letting a vacuum specialist do the troubleshooting outlined below. You can locate a local dealer or contact us for references near you.

How to Test and Troubleshoot a Central Vacuum Motor

What Does it Mean When You Hear a Click When You Try to Turn on the Vacuum?

  • If all you hear is a click at the vacuum unit when you try to start the vacuum motor from inside the house, then the motor in the unit is dead and needs to be replaced.

Strong Smell from the Vacuum Unit

  • A strong odor from the shellac that coats the copper coil windings is an indicator that the motor is about to or has burnt out.
  • If the motor is still running, even if it turns on and off by itself as it is heating and cooling, you can still run the motor until it gives up for good. Note: This may cause the thermal mini breaker to burn out, and then you’d need to replace it or the entire circuit board it is on.
  • If there is no odor, then you will need to turn the vacuum on and observe the motor. If you see lots of blue sparks, read about the motor brushes below.

How to Hot Wire the Vacuum Unit

  • If the motor is out of the vacuum unit, carefully hot-wire it with direct 110 volt leads.
  • There are two leads going to the motor - one black and one white or two black. Use these wires and ignore the green one if there.
  • Hot wire with a patch cord (an AC cord with a regular electrical plug on one end and two alligator clips on the other end) and hook one lead to each of the motor wires (motor wires are not polarity sensitive). Note: Be sure the motor is raised up so the air can enter the bottom of the motor.
  • If the motor still has some life in it, it will start, but if it is going bad, it will only work for 10-15 minutes or less. If it doesn't start at all, it is obviously bad. Sometimes slapping the motor or vacuum unit will jar the motor and get it to work again for a few minutes. Intermittent motors should be replaced.
  • From experience, relays and transformers rarely go out. It is usually the motor that burns out and it usually does so quickly when at life's end.

Always Test the Vacuum’s Wire Connections

  • Take the time to check all of your wire connections - hours can be spent diagnosing a vacuum only to find out it was a bad connection.

How to Check and Troubleshoot Vacuum Motor Brushes

Inspecting the Vacuum Commutator for Motor Brush Problems

  • With the motor running, you will want to inspect the commutator - the center of the less wide part of the overall motor where the two motor brushes (thick graphite / lead looking parts) touch the inner rotating copper armature.
    • It is normal for there to be a slight blue spark right at the carbon brush on the commutator.
    • If the blue spark is large and wrapping around the commutator, then you will need to replace the carbon brushes, but only if the motor bearing is still solid and not at all wobbly.
      • Test that by turning the motor off and pushing on the center shaft, the armature. If it has any play, besides spinning, then replace the motor. If solid then replace the brushes - motor brush replacement instructions.

How to Know Your Motor Brush Needs to Be Replaced

  • Motor brush "lead" is around 3/4 inch when new. When it gets anywhere near 3/8 inch it must be replaced.
  • Note: If it gets too low and scores and damages the commutator, replace the motor. If the copper commutator is seriously damaged - totally blackened and rough - replace the motor.

How to Test and Troubleshoot a Vacuum Transformer

How to Troubleshoot a Vacuum Transformer on a Circuit Board

  • Older vacuums had a separate relay and transformer. Newer ones have all the electronics on one circuit board. On a transformer apart from a circuit board, there will be a total of four wires or more - the black and white are the power/neutral coming in and the colored leads (usually blue and yellow) are the 24 volts going out.
  • Do a simple test by putting the black and white wire to 110 volts, then see if you get a small, low voltage spark by touching the blue and yellow wires together. No spark means the transformer is bad.
  • We have several transformers but they are not for all vacuums. They work for vacuums with a similar set up as pictured below and are available here under electronics and transformers.

How to Test and Troubleshoot Vacuum Relays

How to Test a Vacuum Relay on a Circuit Board

  • Older vacuums had a separate relay and transformer. Newer ones have all the electronics and one circuit board. Our replacement relay will only work for similar wired vacuums as pictured above. A relay has contact points that can go bad but can be tested.
  • When you apply 24 volts (from the transformer) across the low voltage side of the relay (the side with a small copper wire leading up to the terminal posts) then the relay should "click". Note: If you put the wires on the wrong terminals there will be no damage.
  • The replacement relay we sell is part #242 and it replaces the one above and some others. If you are replacing the relay with #242 then you will also have to replace the transformer with the more powerful model. The relay is available here in electronics and relays.

How to Test and Troubleshoot Vacuum Circuit Boards

  1. Ensure that you are powering up the board with the proper voltage (120 or 240).
  2. Attach the power cord white wire to the “Neutral" (NTL) connection.
  3. Attach the black power cord wire to the “power in" or “line" connection.
  4. Plug the power cord into your power source.
  5. Now arc a wire across the low voltage terminals.
  6. You should see a little spark when you touch the terminals and you should hear a "click" inside the board.
  7. If there is no spark, then the transformer is bad. If there is no spark and you do not hear a "click" then the relay is likely bad. Either way replace the entire board.
  8. If you do see a spark and hear a "click" then you want to test for voltage output. Attach any 110 volt electronic device (or functional vacuum motor) to the output terminals - "Motor Neutral" and "Motor Power" for a complete circuit.(240 volt output cannot be tested on a 110 volt appliance.) If the electronic device does not run then you have a bad relay and the board needs to be replaced.

Our boards are made by Alutron, a common supplier for many vacuum brands. Since the basic functions of the boards are the same, our boards can replace other brands. The mounting may vary slightly, and there are no idiot lights on our board. These lights are not necessary, as they are based on hours ran, and not truly helpful data. Here is a sample circuit board, and they are available under electronics and vacuum circuit boards.

Legal Disclaimer: Any action taken upon the information on this website is strictly at your own risk and MD Manufacturing will not be liable for any losses or damages in connection with the use of our website. MD Manufacturing, in any way whatsoever, is not responsible for your use of the information contained in or linked from these web pages.