Topic: Furnace/AC Blower Motor Troubleshooting

[CBJoe]

So I walked into the basement and heard a nice humming sound and noticed a nice burning smell (no smoke).  I found that the blower motor wasn't turning.

I pulled the squirrel cage out and propped it up and turned on the AC... the motor produces a nice hum and turns very slowly for a moment and then stops turning but keeps humming. I tried "jump starting" by giving the fan a good turn to see if maybe the starting CAP wasn't working.  That didn't change the behavior.

I also disconnected the starting cap and tried to give it a jump start, but that didn't work either.

I've already got the motor out as I'm 99% sure that's what it has to be.  But i thought i'd post for another opinion just in case someone has any other ideas. 


thanks for the input, Joe

[scunny]

does the rotor rotate freely, how do the bearings feel. sometimes when a bearing is going the shaft turns blue.

[cb650]

Check for continuity between the power legs.    And no continuity  from power to ground or case.

[CBJoe]

Bearings feel OK although when manually spinning the fan (with power off), it would only rotate for a turn or two.....  without having referenced it prior I'm not sure if that's showing too much resistance or not.

I'll check the continuity between the power legs once I get back home tonight.

thanks, joe

[CBJoe]

Measured 2 ohms between power legs (red/black/blue)

All legs are shorted to common.... but not to housing.

Looks like it's time to start shopping for a new blower motor.... picture of old one attached.  Any suggestions on replacement brand?

I think I can get a discount from Grainger through work.

Thanks, joe

[madmtnmotors]

They are relatively inexpensive, I think I paid $125.00 for mine about a year ago. Similar symptoms, motor quit turning. I had been running the fan 24/7 last spring just to filter the allergens out of the air in the house. It wasn't cold enough for heat to kick in and it wasn't hot enough for AC to kick in and the pollen count was through the roof. After about five weeks continous running the fan motor resigned.

[raymond10078]

2 ohms, when measured with a DC source is not unusual.  A DC source doesn't measure the impedance, just the resistance.  When connected to an AC power source, the impedance is just as important as the resistance.

Anyway, my real point is that some motors have one capacitor that is for starting AND running.  If that capacitor goes bad, the motor won't start or run.  If it were me, and I was tight with my cash, I'd try replacing the capacitor before replacing the motor.

I did try to look up the specs for this motor, by MagneTek was bought out by A.O.Smith, and I couldn't find the specs.

[Skunk Stripe]

Never had this happen but I will watch it. My fan quirk is that sometimes, it will not shut off. I have to unplug it for a couple seconds and when I plug it in, it is fine. Does this once in a blue moon, or a couple times a year so I have not worried about it.

[CBJoe]

Thanks kandrtech.... I did find the A.O. Smith website and it listed a replacement motor as Model DL1036 that has the following ratings.

I'll look into trying the Capacitor first.  I've got the motor out, but i'll just wire it back up and see what happens with a new capacitor.  Joe

Horse Power:   1/3
Amperes:   4.9
Frequency:   60
RPM:   1075/3 SPD
Voltage:   115
Number of Speeds:   3
Motor Type:   UF
Frame Size:   48Y
Nema Suffix:   Y
Service Factor:   1.0
Phase:   1
Enclosure:   OPEN
Bearings:   SLEEVE
Ambient Temperature:   40
Insulation Class:   B
Rotation:   REVERSIBLE
Protector:   AUTOMATIC
Agency Approvals:   ULCSA
Capacitor Rating:   7.5MFD/370VAC
Duty Cycle:   AIR OVER

[GammaFlat]

I've had blower motors with the same symptoms... wants to turn some but won't build speed or just sits and hums.  I replaced and all was fine. 

[CBJoe]

We'll the weather's been beautiful here in indianapolis over the last couple weeks... so i've been a slacker and hadn't fixed the AC yet.

But 90+ degree weather is creepin' in so I figured i'd get a move on.

Motor and Run Capacitor have been changed and I just got it all buttoned up.  Everything works and it's a heck of a lot quieter than before.... also now my lights don't dim when the blower kicks on 

Got a heck of a deal on parts after i realized that i could use my company account at Granger to buy parts.  Only cost me $90 in total!

thanks for the input.

Joe

[Don R]

When mine went it filled the house with smoke, Wife called the fire dept, The motor and start capacitor were fried. A new motor and all was good for two weeks, came home and the motor was barely running and clicking. One leg of power from the power co. was only 65 volts, Some of the lights were dimming, I went to the old folks house next door, same deal. The distribution box in the yard between our houses had a corroded connection. Aluminum wire. Just saying, keep an eye out for other issues sometimes.