Troubleshoot Motor, Relay, Transformer, Motor Brushes

How do you test and troubleshoot vacuum motors? Test a vacuum transformer or relay, or even a vacuum circuit board? We have answers and recommend a professional vacuum specialist follow these directions to troubleshoot vacuum components. You can locate a local dealer here or contact us for references near you.

Test and Troubleshoot the Vacuum Motor: If you try to start the vacuum motor from inside the house and all you hear is a click at the vacuum unit, then the motor in the unit is dead and needs to be replaced. Sometimes you will detect a strong odor from the shellac that coats the copper coil windings. This is an indicator that the motor is about to or has burnt out. If the motor is still running, however, even if it turns on and off by itself as it is heating and cooling off, you can still run the motor until it finally gives up for good. The only damage that can happen with that is the thermal mini breaker may burn out and you'd have 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. 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). 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 or 15 minutes, and sometimes much 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. Intermitant 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. 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.


Check and Troubleshoot Vacuum Motor Brushes: 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 - but 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. Motor brush "lead" is around 3/4 inch when new. When it gets anywhere near 3/8 inch it must be replaced. 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.
Test and Troubleshoot Vacuum Transformer: 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.

Test and Troubleshoot Relay: 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". 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.
Test and Trouble Shoot 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 who supplies most other brands as well as ours. Our boards can be used to replace other brands as the basic functions are exactly the same. The mounting may be a little different and there are no idiot lights on this board. These lights are really not needed as they are based on hours ran, and not truly helpful data. Here is a sample circuit board and they are available here under electronics and vacuum circuit boards.