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Posted: 1/21/2013 6:25:26 AM EDT
[Last Edit: 1/21/2013 6:36:23 AM EDT by Leisure_Shoot]
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
Link Posted: 1/21/2013 6:28:20 AM EDT
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.
Link Posted: 1/21/2013 6:34:16 AM EDT
[Last Edit: 1/21/2013 6:41:47 AM EDT by GunMonkwy666]
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
Link Posted: 1/21/2013 6:37:28 AM EDT


Direct Drive Blower Motor, Permanent Split Capacitor, Open Air-Over, 1/3 HP, Nameplate RPM 1075, Voltage 115, Full Load Amps 6.5, 60 Hz, 1 Phase, 48Y NEMA/IEC Frame, Service Factor 1.0, Ambient 40 C, Insulation Class B, Number of Speeds 4, Torsion-Flex Bracket Mounting, Sleeve Bearings, Thermal Protection Auto, Rotation CW/CCW, Body Dia 5 5/8 In, Length Less Shaft 4 3/4 In, Shaft Dia 1/2 In, Shaft Length 5 1/2 In, Capacitor Required 2MDV4
Grainger Item # 2FGP7
Price (ea.) $146.95
Brand A.O. SMITH
Mfr. Model # 753A
UNSPSC # 26101603
Ship Qty. 1
Sell Qty. (Will-Call) 1
Ship Weight (lbs.) 17.6
Availability Ready to Ship
Catalog Page No. 70
Country of Origin
(Country of Origin is subject to change.)
Mexico




Link Posted: 1/21/2013 6:39:38 AM EDT
[Last Edit: 1/21/2013 6:44:46 AM EDT by Leisure_Shoot]

Originally Posted By GunMonkwy666:
This:

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


I thought blower motors were one speed??
It has four different wires, depending on which speed you need, you power that lead to the furnace... in this furnace you use the Hi Speed for Cool, and Low or Med-Low for heat.

But does the system have a startup capacitor?? This gives the motor a kick to get it started.
The motor does not have a start capacitor, just run capacitor. Neither did the original. This is an exact match for the original, other than brand name.

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


Or

It is it dual voltage motor that will run off on 220Vor 110V??? Different lugs for different voltages.


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


Capacitor Required2MDV4
yes, I bought the capacitor, and installed it. Just in case it was bad, I took the old one, and swapped it in to see if that was the problem. Same sound.

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

Permanent-split capacitor motor

Another variation is the permanent-split capacitor (PSC) motor (also known as a capacitor start and run motor).http://en.wikipedia.org/wiki/AC_motor#cite_note-TMotors-19][19][/url] This motor operates similarly to the capacitor-start motor described above, but there is no centrifugal starting switch,http://en.wikipedia.org/wiki/AC_motor#cite_note-TMotors-19][19][/url] and what correspond to the start windings (second windings) are permanently connected to the power source (through a capacitor), along with the run windings.http://en.wikipedia.org/wiki/AC_motor#cite_note-TMotors-19][19][/url] PSC motors are frequently used in air handlers, blowers, and fans (including ceiling fans) and other cases where a variable speed is desired.

A capacitor ranging from 3 to 25 microfarads is connected in series with the "start" windings and remains in the circuit during the run cycle.http://en.wikipedia.org/wiki/AC_motor#cite_note-TMotors-19][19][/url] The "start" windings and run windings are identical in this motor,http://en.wikipedia.org/wiki/AC_motor#cite_note-TMotors-19][19][/url] and reverse motion can be achieved by reversing the wiring of the 2 windings,http://en.wikipedia.org/wiki/AC_motor#cite_note-TMotors-19][19][/url] with the capacitor connected to the other windings as "start" windings. By changing taps on the running winding but keeping the load constant, the motor can be made to run at different speeds. Also, provided all 6 winding connections are available separately, a 3 phase motor can be converted to a capacitor start and run motor by commoning two of the windings and connecting the third via a capacitor to act as a start winding.





Link Posted: 1/21/2013 6:40:12 AM EDT
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.
Link Posted: 1/21/2013 6:42:44 AM EDT

Originally Posted By d_rob1031:
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)
Link Posted: 1/21/2013 6:53:57 AM EDT
Originally Posted By Leisure_Shoot:

Originally Posted By d_rob1031:
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.
Link Posted: 1/21/2013 6:55:56 AM EDT
[Last Edit: 1/21/2013 6:56:58 AM EDT by Leisure_Shoot]
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?
Link Posted: 1/21/2013 6:57:43 AM EDT
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
Link Posted: 1/21/2013 7:00:26 AM EDT
[Last Edit: 1/21/2013 7:01:46 AM EDT by d_rob1031]
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.
Link Posted: 1/21/2013 7:04:48 AM EDT
Maybe a bad or weak ground somewhere

Damaged or melted plug where it gets power from the wall outlet
Link Posted: 1/21/2013 7:26:32 AM EDT
[Last Edit: 1/21/2013 7:31:12 AM EDT by Leisure_Shoot]

Originally Posted By d_rob1031:
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.
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?

Link Posted: 1/21/2013 8:12:06 AM EDT
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.
Link Posted: 1/21/2013 8:35:47 AM EDT

Originally Posted By d_rob1031:
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...

Motors have a lot of torque.

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"!
Link Posted: 1/21/2013 9:34:02 AM EDT
Originally Posted By Leisure_Shoot:

Originally Posted By d_rob1031:
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...

Motors have a lot of torque.

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!
Link Posted: 1/21/2013 10:44:29 AM EDT
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.
Link Posted: 1/21/2013 11:54:35 AM EDT
yeah, sounds like I will be swapping it out. thanks again.
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