My furnace blower had a bearing go bad.  



I purchased a replacement motor from Grainger.



The specs are an exact match. The only difference being the original was a GE, and the new on is a Century.
When the motor starts, for 1/2 a second, there is a very loud hum/resonance sound.



It sounds like metal duct work vibrating, and I assumed that's what it was, at first.



I ended up taking the blower fan cage out, with the motor installed, and running the motor that way (from the furance control board), and the noise remains for the first second.



Just to try it, I swapped the run capacitor with the original, since they had same specs.



What I did determine is that the motor is starting up pretty slow.  I can actually hold my hand on the shaft for the first half second, as it starts to spin weakly.



It is a four speed motor, 1/3 HP, 115V, 5.6A.



Grainger Part # 2FGP7
I called Grainger and they told me it sounds like the motor isn't getting enough voltage at start up.



What can I do to test this situation? Is it as simple as putting a tester on the two input leads off the circuit board, to see if it is getting 115V? Do I need to check amps too?



Can I remove the blower housing again (ugh) and run the motor and fan off house current from an extension cord?  



FWIW, the motor has a reversing plug, so I don't think I can really hook it up incorrectly.






Here's a video of it... the vibration sound is definitely not the furnace metal.. it does it when I run the fan/motor when it is no installed in furnace.






.
thank you


 

I think they call it a hot start.  But it's a capacitor that you install inline with the power lead to the motor.  It gives the motor that extra kick of juice it needs when it starts up.

This:

"It is a four speed motor, 1/3 HP, 115V, 5.6A.
Grainger Part # 2FGP7"


I thought blower motors were one speed??

But does the system have a startup capacitor??  This gives the motor a kick to get it started.  

Motors with a big hump off the side have a built in startup Capacitor.




OK - looked it up 115 volt motor but does require a capacitor from the spec sheet -


Capacitor Required2MDV4

regarding the capacitor, this is what I found on Wiki.....





 

The dual voltage is accomplished by how the motor leads are connected.  The wire size/lug sizes are the same.

There will be a diagram on the motor showing you what leads to put together for 220v and for 110v.

It isn't a dual voltage motor, and there is no 220V capability, according to motor specs (above)



 

To be quite frank with you it is cheaper 99.99% of the time to replace the motor if you find the direct replacement.  Especially motors of this sort.  

IF you are comfortable opening the motor up and inspecting it I might be able to walk you through it.  Typically on single phase motors it is 1 of 2 things.  Either the start capacitor has crapped out or the centrifugal switch is dirty and has either quit making contact or has quit "moving".  If you open the motor and it is dirty inside, try freeing the switch up with standard lubricants and cleaning.  Put it back together and try again.  If that isn't it, change the capacitor.  If that isn't it, you're buying a new motor... you have a winding (either start or run, sounds like the start) failing on you.  Motors of this size/style aren't worth having new windings put in.

As a personal note, I despise single phase motors.  I work with 3-phase motors for work and they are simple, less expensive and run a hell of a lot longer... sadly 3-phase isn't an option for you.

It is a new motor, I just bought it 2 weeks ago.  It runs fine, it is just noisy on start up.



Are you saying there is a start capacitor inside, in addition to the run capacitor that is mounted outside?

Or possibly, it has bad windings from the factory?

sounds like the start up circuit is not kicking in and it is single phasing on start up.
it most likely starts on low speed and it needs the other phase to get going, that is
what the capacitor does, it adds a phase to the motor if it has split phase winding's

Sorry, my reading comprehension sucks today and I can't watch the video at work.

The capacitor on the outside is the only one.

I think you may have a bad motor since it is a new one.  It sounds like your start winding isn't working properly.  A single phase motor will "click" after a few seconds of getting up to speed on start up.  That is the centrifugal switch going from start to run winding mode.  Do you hear that?  If not, your switch is bad.  If you do hear it, it sounds like your start winding isn't feeding the proper amperage.

ETA:  Some motors have 2 capacitors on the outside.  This is a design choice.

Maybe a bad or weak ground somewhere

I don't hear a click after it starts up.



When I pull the blower fan back out, can I wire it to an extension cord, just to listen to it start up free and clear, before I take it back for exchange, in order to verify that the furnace board isn't bad?
 

You should be able to but be careful of the following:

When motors start up they pull a tremendous amount of amperage for a few seconds.  Make sure the plug you are using is on a circuit that can take the amp load.  Turn off anything else on the same circuit, unplug anything expensive, etc.

Motors have a lot of torque.  Even a 1/3HP motor will have enough to jump or flip itself (if it's properly working, that is).  Make sure you have it well secured.

If something is wrong on the inside it can get hot enough to seriously burn your skin.  Make sure it is electrically grounded to the floor/table/something.  

I hate to say the obvious but make sure the leads are well separated and insulated.  They will instantly melt themselves together if they touch.  

Before you do anything though, open up the junction box and smell inside it.  If it has a burnt smell, the motor is bad, don't attempt to hook it up, it's not safe to run it.

OK thanks.

I will leave it int he fan housing, and secure it to workbench.

No worries about the electrical connection.

I'll be using wire nuts, etc...






That's the thing about this motor, it is slw to get going, like how you described a "start switch"... it takes per[ahs 2-5 seconds to get to full speed, and if I shut it off, and then kick it back on while fan is still spinning a little, it starts up perfectly, so I assume it has something to do with the start sequence.  



Thanks for the "tech support"!



 

When motors are not turning they use a lot of current (amperage) to get it started and up to speed.  The extra amperage they use is called "inrush".  If your motor is already turning, the inrush current needed is very, very little which is why it starts up better when it is already spinning a little.  The motor should be up to speed from 0 in a fraction of a second.

Everything you tell me points to start winding or capacitor trouble.  

And you are quite welcome!

I just happen to work for Baldor Electric,, We make electric motors...Since it is a new motor, It could be anything from wrong bearings/bushings, to a bad weld/crimp on the leads. Sometimes they even get sent out with wrong wire size in winding's, after they have passed the tester.
Like everything else, bad parts get shipped out. I would return motor for a replacement, or have motor tested at a repair shop. But I would just return it.

yeah, sounds like I will be swapping it out. thanks again.