Electricians - Help me diagnose my vaccuum

I’ve got a central vaccuum canister of unknown age that’s been having problems lately. It had been making sick noises for a little while, and then finally up and died. The noises were cyclic in nature, i.e. the sound would speed up for about 10 seconds, then slow down for about 10 seconds, repeatedly. I assume that something was being loaded heavily.

I replaced the circuit breaker which fixed it for a couple of uses, same noises but it worked. Died again. Replaced breaker, died again.

My first inclination is that the motor (ball-bearing type) is on its way out. I made some calls today and discovered a new motor would be about $260.00. More than I want to spend. So before I bite the bullet, I want to rule out other problems.

It’s pretty simple electrically. There’s a switch, circuit breaker, relay, transformer, and motor. So the only other failure items I can see are the relay, transformer, and motor.

I must confess my electrical knowledeg is sub-par in this area (I’m a mechanical engineer, I slept through circuits). I guess my real question is what are the failure symptoms of relays and transformers and could they be causing the odd cyclic noise I hear?


Actually, it sounds to me like it IS the motor (or the blower attached to it). But don’t panic yet. If you’ve got an hour or two and normal hand tools, you can probably re-build it for far less than $260. I do it a few times a year at work.

Carefully (patiently) dis-assemble it (paying careful attention to how it will go back together, of course). Don’t force anything, and pay attention to how things are “clocked” so the assemblies will be more-or-less balanced when re-assembled.

Look for anyplace where the blower’s vane assy(s) may be rubbing the housing, check the bearings and brushes, and clean it out thougoughly. Replace any bad parts and re-assemble.

Replacement bearings and brushes are available at your local industrial supply (Grainger- http://www.grainger.com ). Usually under $10. Just take in your old part(s) and they’ll find it for you.

Even if you can’t fix it, you’re only out a little time.
And if you DO need a new motor, the industrial supply can probably get you one cheaper.

[sub]i am not affiliated with the company linked above in any way (beyond their repeated saving of my butt in difficult situations)[/sub]

It could be the bearings of your motor. As they near siezure, the motor is harder to turn, drawing more current.

Or, is there a belt from the motor that also turns a roller brush? Maybe the roller brush is binding, causing the same symptoms for the same reasons as bad bearings could.

If you’re replacing breakers, then you know that somethings making the motor draw more current than it should be, so I’d have to rule out switch or relay. If the insulation on the transformer or the motor windings is breaking down, causing a short, then that would draw more current.

Does the motor “cycle” like this when there’s no load? I.e., when you put the vacuum on its back and disconnect the belt, if any?

Sounds like the motor. Something is heating up and causing a fluctuation in current drain. You didn’t say what type of motor. Universal-type? Check the electrolytic capacitor (usually a bulky cylindrical can screwed onto the motor body). Replace that (Cost should be <$25). If that failes, get a new motor.

Thanks for the replies.

The vaccuum does cycle with no load (it’s a central vac canister, so I can’t put it on its back, but if I just run it without trying to suck up Cheerios my daughter has scattered like confetti about the room it still cycles). There don’t appear to be any belts. It pretty straightforward. I think the motor assembly contains the blower. I didn’t see any external capacitor either. But you know what, if I’m looking at a few hundred to replace the motor (a complete new unit would be about 500 clams), I might as well take it apart and see what trouble I can get into. Thanks for all the tips.

BTW, a new Grainger store just opened a few minutes from me, I finally have an excuse to go there.