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Discussion Starter · #1 ·
Left the fan in the "ON" position on the thermostat yesterday to help circulate air in the house and forgot about it- came home to find a loud humming noise from the boiler room, and no air movement at all.

Flipped the shut off switch and let it cool down a bit before trying again. Same thing happened when I turned it back on. Motor won't spin up to speed, makes loud humming noise. So here's what I've done to troubleshoot so far:

I can see it trying to turn as it hums, so I figured it was probably the capacitor. I took the cap out and brought it to a local shop to find a replacement. Replacement tries a little harder to turn, but still can't bring it up to speed.

So, if it isn't the cap, I thought maybe the motor had too much caked on dust and needed to be cleaned. I've only lived in this house for 3 years, but it was built in the 60s and who knows when the last time it was cleaned out is. I say this because I've never done it before so I was totally figuring it out as I go. Managed to remove the screws that hold the blower in place, pulled it out, and went at it with a vacuum and compressed air cans.

After putting it back in and flipping the switch, it *DID* power on and start spinning (fan in the ON position on thermostat)! But I shut it off and put the cage door back on, then flipped the switch to heat and lo and behold, it does not start. Just loud humming. I even put the fan "ON" again, and it did not start.

I thought maybe I need to add some oil? But I can't figure out where oil would go on this thing. The motor has an old barely legible sticker that says it has sealed bearings and does not need oil, so maybe that can't be it either?

After poking around and putting it all back together again, I flipped the switch on and I could hear it *trying*, but not starting. It seemed like it was getting close, so I shut the switch and waited 5-10 seconds, then tried it again. On the 3rd attempt at this, it spun up. At this point, I was afraid of losing it again so I just left the fan in "ON" and turned the heat on.

Once the house was up to the right temperature, I felt like I needed to shut it off. First of all, leaving the fan on 24/7 can't be the solution- this whole thing started when I left it on yesterday for a few hours instead of auto.

So at this point- It appears not to be the cap, I already tried to clean it, and the sealed motor design doesn't need oil. So what else could it be? Is the motor just dead? I feel like I see it trying to turn and sometimes it DOES spin up and just work, so what could it be?
 

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We might also check to see that the motor electrical connections and the wires adjacent to those connections are in good shape.
A voltage check to make sure it's getting 120.
An Amp test to see if its drawing more than it's spec'ed out for when it's running.
That the squirrel cage rotates freely.

.....but 95% of the time we will just end up changing the motor.
 

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Motor start windings sound like they are bad. Clearly not completely cooked, but failing. If you changed the cap for the same ratings, and you do actually always have power to it when you want it to run then it's the motor.

PS. Those motors are designed to run non stop, but their life is measured in run time hours. So the more it runs, the faster it'll die. (5-10+ years should be expected though)

Cheers!
 

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Discussion Starter · #4 ·
Thanks for the responses, guys!

I was able to warm up the house last night by leaving fan ON, but I was nervous to leave it running in case it burn out again in the middle of the night. So I flipped it back to auto. Sure enough, it wouldn't spin again later. Kids slept with space heaters again, I turned the unit off.

A bit more alarming- I found a wire cap next to the fan when I was cleaning it out. I don't see any hanging or loose wires, everything appears to be connected. I'm wondering, maybe there is a bad connection somewhere I can't see? Is it possible to have wires like that capped inside the motor/blower assembly? Maybe something came undone?

 

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Discussion Starter · #5 ·
Some more pictures to illustrate:

Here is my blower assembly. There's a little box to house the connections and capacitor as you can see on the side.


Here's that box opened up (which I had to do in order to change the cap anyway):


The only wire that isn't connected is this red one, which appears to have been purposely not connected and taped over itself. I don't think that's where this blue wire nut came from, and don't see anything it would connect to anyway.


I did not open up the squirrel cage / motor assembly- I went at it with a vacuum and compressed air can to clean it out while pulled out, but never disassembled. Are there any connected wires inside of there that this blue cap may have come from? I assumed everything in the motor is hard-wires, and these cables come out and connect to the rest of the system with wire connections in that box (with the capacitor). Am I wrong in my assumption? Should I take apart the blower and remove the motor to check the connections inside (if there are any)?

...or do you guys think I should just give up and buy a new motor? I'm *this* close to just hiring an HVAC pro to take over. :(
 

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Sounds like your motor is bad. If it sat humming and trying to start for a long period of time the windings would be be bad. Most systems have two speeds hooked up, high speed for cooling and low speed for heat. If a three speed motor was put in you would have an extra wire. Don't be surprised if the new motor wires a little bit different on the new motor.
 

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Discussion Starter · #7 ·
Sounds like your motor is bad. If it sat humming and trying to start for a long period of time the windings would be be bad. Most systems have two speeds hooked up, high speed for cooling and low speed for heat. If a three speed motor was put in you would have an extra wire. Don't be surprised if the new motor wires a little bit different on the new motor.
Ok. So a new motor then. Stinks because I have a service guy on his way over right now. I probably could buy a new motor and just follow advice on this forum or others to put it in myself, but my family is pressuring me to get this fixed sooner.
 

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Ok. So a new motor then. Stinks because I have a service guy on his way over right now. I probably could buy a new motor and just follow advice on this forum or others to put it in myself, but my family is pressuring me to get this fixed sooner.
Did tech install new mtr??? Some company's have flat rate charge $67.00 mtr or $400.00 mtr = XXXX installed no matter what the mtr cost. What is the rest of the story???????:vs_bananasplit:
 

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Discussion Starter · #13 ·
Hey sorry I didn't log back on and report the rest of the story right away!

So, the service guy came and tested connections, cleaned and lubricated the motor, etc, and then drew the same conclusion. Motor needs to be replaced.

The good news is, I learned a lot about how it works and he answered a lot of my questions and was really helpful. So much, in fact, that he helped me source a new one and walked me through what to do in order to replace it in order to avoid an additional service charge (I'm very thankful for guys like this).

The motor was something like $120-150, I think. I took out my old one, cleaned up the squirrel cage a bit more before reinstalling, and it seems to be working great now.
 

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If your furnace blower motor hums when it’s switched on but at the same time does not actually turn, the capacitor may be damaged. This problem of getting a humming noise along with little to no spinning is very common with motors that do not have good quality capacitors. You should replace the capacitor with a good one and the blower motor will work smoothly. Once again, this may initially trace back to a simple blocked filter.

If your motor does not run even after replacing the capacitor, it is most likely that the unit overheated. You should reset the safety buttons located at the side of the unit.
 

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Discussion Starter · #15 ·
If your furnace blower motor hums when it’s switched on but at the same time does not actually turn, the capacitor may be damaged. This problem of getting a humming noise along with little to no spinning is very common with motors that do not have good quality capacitors. You should replace the capacitor with a good one and the blower motor will work smoothly. Once again, this may initially trace back to a simple blocked filter.

If your motor does not run even after replacing the capacitor, it is most likely that the unit overheated. You should reset the safety buttons located at the side of the unit.
Thanks for the input! As you can see in my original post however, the cap was the first thing I tried.
It wasn't a simple overheat or blocked filter. I had cleaned everything out, even tried changing wiring, etc... in the end, I replaced the motor and now everything is working great. In fact, I can already tell that the air flow is stronger than it was before, so I'm wondering if my fan motor had been weak and already dying when I moved in 3 years ago (this would also explain why my AC unit would occasionally freeze up every summer that I've lived here).
I learned a lot about my HVAC system from this experience, thanks everyone for their input and help!
 
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