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Discussion Starter #1
It's summer, and it's hot....everywhere. Summers here in SoCal have that "dry heat" which makes for some stinging sun rays where everything absorbs heat and then releases it all night long as opposed to having a hot wet blanked wrapped around you as I know other parts of the country are for summer. And this is what brings me to my issue and question.

My home's AC unit broke down yesterday.

It's not the first it's happened either. The entire HVAC system is at least 20yrs old and this is actually the third time it's happened since moving to my home three years ago with last year's issue being the same as it is this time around. The issue this time (again) is that the blower motor in the furnace that pushes air throughout the house has died again. Last year, it wasn't an issue as I found a refurbished replacement unit on eBay and it has been working great up until yesterday (AC for summer and heater for winter).

Well, this time around I'm not able to find my unit on eBay, instead I'm finding similar units with varying specs that are not identical to mine in one fashion or another. I'm going to replace the entire system here in about a month or so, but I'm not sure if I want to have my family deal with the summer heat while I'm at work until we do get that whole new HVAC system or should I find a similar enough motor motor unit and replace it.

The problem with finding a replacement now is that I'm unsure of the wiring setup for a replacement unit in terms of what to do. The last replacement I got, like I said earlier, was an identical replacement so it was basically a R&R job. With a different spec'ed blower motor, I'm sure the wiring setup will be completely different.

My not wanting to have my family suffer during the summer heat of course makes me want to replace the blower motor for now until I can have the entire system replaced. For that, I'm seeking the advice of anyone here who can help me out with this. My blower motor's specific PN is 5KCP39PG B668S. However, searching eBay, Amazon, and even Google for that PN comes up with no results. However, searching for the prefixed PN, 5KCP39PG, I get a plethora of hits but nothing identical to what I need. This is where I need the advice of anyone who can help me out here.

These are the old unit that broke down last year.



 

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I know youre trying to keep it a little low budget - but why bother keeping on fixing something so old ? I am sure a more efficient one would save you money on your bill and there may be some incentives with the power company.

I held out for a long time on my unit from the 60's .. but when it finally gave out, I decided to replace it with a brand new one and I saw a huge drop on my bills.

- Dan
 

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I know youre trying to keep it a little low budget - but why bother keeping on fixing something so old ? I am sure a more efficient one would save you money on your bill and there may be some incentives with the power company.

I held out for a long time on my unit from the 60's .. but when it finally gave out, I decided to replace it with a brand new one and I saw a huge drop on my bills.

- Dan
Dan:
See this line; it seems like a new HVAC is already in the works but I'm guessing that it takes a while to build up the scratch so spending $125 now is better than the alternative (sweltering house)
I'm going to replace the entire system here in about a month or so, but I'm not sure if I want to have my family deal with the summer heat while I'm at work until we do get that whole new HVAC system or should I find a similar enough motor motor unit and replace it.
Please note that I know NOTHING about HVAC systems but a little something about wiring diagrams. You can see if on the left side of the label you posted and its consistent with these notes.
http://archives.hvacmechanic.com/archives/15872


Brn — goes to Capaciter
White - goes to the other side of the capaciter and then to Line
Black - Line

Three more wires for speed:
Black - High Speed
Blue - Med High
Yellow - Med Low
Red - Low

Capaciter is 12.5mFd @ 370V

---
If you replaced the burnt out motor with another one of slightly different spec, example, THIS ONE:
Furnace Blower Motor 5KCP39PG | eBay

Just match the wiring (looks the same at first glance but it's your house so double check)

AND replace the capacitor with the one specified by the new motor.
For example, this one calls for a 10mFd @ 370V cap

The one thing I cannot help you with is I dont know if you can sub the existing 12.5mFD cap for this one.
Q: Do you know who might be able to answer that question?
A: A guy like Hoarder158 to sells used HVAC parts on Ebay.

Just to be safe though a new cap is only $8.25 so in your shoes, I'd just buy a new cap and call it a day. I don't know how tight money is for you though but I can imagine not having AC when temps climb into the 90s can make your house uninhabitable.
Run Capacitor 10 MFD 370V Round AC Electric Motor HVAC 370 Vac V Volts 10 Uf | eBay


Regards,
-g
PS. Engr school was 16 years ago for me and I've never worked on an AC system in my life.
 

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I never knew this (the only wiring diagrams I'm used to are mostly small electronics/automotive vs higher voltage/current applications) but apparently proper cap sizing is important for large current electrical motors.


I kinda knew this in theory but here's some interesting comments about WHY you need a cap within spec:

1) Too small a cap and the motor will fail to energize
2) Too large a cap and you get an uneven magnetic field inside hte motor -- causing irregular rotation and therefore noise, increased energy consumption, and overheating.

CAPACITOR SIZING DILEMMAS
https://en.wikipedia.org/wiki/Motor_capacitor

Bottom Line: replace the cap to match the new motor.
-g
 

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PS. Engr school was 16 years ago for me and I've never worked on an AC system in my life.
Yeah thats pretty much what I do for a living. Installing refrigeration pipes for industrial buildings is just a small part of my scope, but I have been doing a lot of them with my experience/knowledge.

What im talking about is installing a new controller for the motor also - something capable of running the motor at variable speeds (Pulse Width Modulation ).

Summer is pretty much the worst time to be buying anything A/C related though.
 

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Just get a Motor 3/4 Hp, 1Ph, 110-120V with the same shaft size. Amps will be consistent with it being 3/4Hp and 1075RPM is fairly standard.

Rotation is determined how the capacitor is connected to the motor, it not a big deal if you get it wrong just a matter of swapping which terminal it connected to (IE: on a Baldor motor swap between 3 and 5)



As for the HVAC system replace the whole thing now (ducts and lines should be ok). Last year I finally replaced my outside unit then with in a couple months blew the A coil (heat pump), this year got new A coil. So now I have the last of the R-22 systems instead of getting all new. Which is fine until have a problem again.
 

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Depending on your house's electrical connections, the capacitors can go bad a lot faster; bad wiring from the pole can cause voltage drops that make stuff with motors fail faster.

Also storms, etc.; I've had issues myself.

Failing storm damage, the real deal over time is that the motor draws more current as it ages, and eventually starts killing caps by overcurrent.

It draws current thru the capacitor until the motor reaches it's normal speed, then a centrifugal switch opens, and disconnects the start circuit. :) See the problem?

I'd replace the motor with a Form-Fit-Function replacement, (same plate ratings, size, and shaft connection) and replace the system at your leisure.


I'd recommend Ball-Bearings throughout, other types fail faster.

Everything S4gunn said was good; I'm an EE myself.

The Totally easy fix is to buy a box of capacitors, and replace them as needed, until one explodes.

Then the motor is really, REALLY dead. :grin2:

I wouldn't do that. :)
 

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Ideally Grog that would be best but I doubt the motor has a data plate still, and a replacement fan blower will be fine (frame size should be the same).
 

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Discussion Starter #10

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With the linked one being a 48Y go with the 48 dimensions (Y denoted non-NEMA-standard mounting) and compare to yours.
Electrical Motors - Frame Sizes
 

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Discussion Starter #12

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Use a tape measure and compare the measurements. I suspect its the same.
 

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Discussion Starter #14
Will do. I'll check it out when I get home. Since I'm going to be measuring the old defective unit I already have out, I'm guessing I only need measurements D and E? Or do I need D and F+F+BA+NW?
 

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Since it looks like you lack a mounting foot E and U is all you need. E is the diameter and D is radius plus the mounting foot. If you have access to a machine shop U doesn't even need to match since could make an adapter. U (shaft diameter) is the only thing I'm thinking would actually pose a problem.
 

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Discussion Starter #16
I have mounting hardware as the current (presumably) broken motor is still installed in the housing. I'm just not sure if the mounting hardware will fit a different motor all together (I'm looking at the one from Home Depot that was linked earlier).
 

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Discussion Starter #17
OK, so just now I went to the blower unit and flung the fan by hand (I used long set of 90* pliers to get in there) and it was enough to actually get the motor going and cold air is starting to warm up my 92*F home. Does this mean that the motor itself is good and all I need is just the capacitor?
 

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Possibly. You'll have to amp-check the motor to make sure that it's not exceeding its amp-rating. If it's as worn as its age suggests, it may be pulling too many amps, and is therefore on the verge of full failure. It would be great if you could get by with a new capacitor, though. Even if it's just for a short while. Like S4gunn said, make sure it's the right capacitor.
 

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OK, so just now I went to the blower unit and flung the fan by hand (I used long set of 90* pliers to get in there) and it was enough to actually get the motor going and cold air is starting to warm up my 92*F home. Does this mean that the motor itself is good and all I need is just the capacitor?
I had an old box fan like that..For years I would start it manually with a stick, once it was going it was good..

Eventually, that didn't even work when everything on the inside of the motor dried up..

Had it been properly lubricated throughout it's life, I'm sure the motor on that fan would have lasted for years..

Of course, I was only 12 at the time..So I didn't even know how to do that.. :tongue:

Around here, we have a place that rebuilds electric motors..

I would suggest either looking in the yellow pages (Do people still do that?), or online for a shop near you that does that..

It might be cheaper to rebuild your old motor, than buying a new one..The shop will be able to tell you what your cheaper option is..






Rayo..
 

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Discussion Starter #20
Well, I ordered a new cap from Amazon last night as it was only $13 shipped to me. If that gets me by for the summer, I'll be happy. The wife and I have been planning on replacing the entire HVAC system in our home with next year's tax return, but if this quick and cheap fix doesn't do it, we will have to shift our home projects around and do the HVAC right now instead of this coming spring like we've been planning on.
 
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