Hi guys

Long story short is my Furnace Blower motors is making a humming noise and not starting. So far I have replaced the Run Cap (with no hope), checked the wiring on the furnace, checked the high temp switch.


Longer story, this was my first winter with a NEST-E (added it this summer) and my system didn't have a C wire - actually it did, but I didn't see it as it was pushed in the wall since the previous thermostat didn't use one. After seeing my NEST going on/off I looked into the issue found that a C wire was required, looked at my wiring, found the C wire, connected it and thought it was gonna be ok.

But the heater would still not work and digged further. The blower motor is getting power, but it hums and doesn't start. Replaced the run cap, just in case - no help. I tested with a multimeter the high switch which is fine. The High Switch is wired in series with that box (See picture below) that is a L406A2782 from Honeywell (fan and Limit control).

The blower motor has 6 wires, 2 of which are wired to the cap. The other 4 (in picture below) are black/white/blue/red.

The blue wire is terminated inside the control box and is not wired to anything, weird. the red wire goes to the Honeywell fan and limit control and in turn to the high switch. black and white are 110V and, the motor is getting 110V just fine, just doesn't start. I am not sure what type of AC motor that is and what the red wire does, but I am sure it does something, not sure what.


Lastly, I've read a lot of stuff online, a lot of articles refer to the a "reset switch" on the motor/blower. I don't see one, and I've reached as far back as I could and couldn't feel one. I'm not sure if it does have one or not.


Oh, and the rotor spins freely, no blockage or anything.


The blower was working fine this summer. I am kinda of suspecting it went out when NEST E ran without the C wire, which caused it to turn the furnace/blower on and off, probably too much.


Anyway that's all I have, fell free to ask any question. Hopefully I can get this fixed asap, it's kinda cold heh

link to all 4 pics:

https://imgur.com/a/YZM6nZ8

thank you guys

 

That's a three speed motor. The speeds are red = low, blue = medium and black = high. White is neutral.
If you have the thermostat set to FAN ON..... it energizes the G wire and that is usually the high speed for A/C. The fan/limit control is activated by heat and uses a slower speed. In this case.... red or slow speed.

There should not be two windings energized at the same time. Disconnect either the red or black so that only one is connected. See if the motor is normal then. Unless you've changed wiring..... the motor should still hum. The hum is caused by it not being able to start from bad bearings. Typically the one closest to the blower wheel.

 

Thanks TJ,

I will try to disconnect the red wire (the blue wire is not connected to anything).
I do have 110V between black and white, which is normal and should run the motor at full speed.

As I mentioned I can spin the blower blades by hand with no effort, there does not seem to be any resistance whatsoever.

 

Yeah..... the motor will spin freely until it's powered. Then the armature gets pulled towards the windings and you get a hum. I just changed my own blower motor recently. Same issue.

Try lifting up on the blower wheel. ANY play is too much.

 

aww bummer.
I'll go check that play.

did you replace the bearing or the entire thing?

 

I changed the entire motor. It happened late at night so what I did is...... my motor is in a belly clamp. That's a clamp that encircles the motor. I took the motor out of the clamp and turned it 180 degrees. It ran for two days like that..... complaining the whole time.

 

Merry Christmas all

I took the blower off the furnace but the motor shaft won't loosen from the rotor.
I loosened the set screw but the shaft is really not moving. I've tried a pair of adjustable wrench, and a small hobby vice which gives me a little bit more level to torque it out to no avail.
I have applied a generous amount of liquid wrench and let it soak for an hour, didn't help.

would you by any chance have a good tip to loosen the shaft?

by the way the whole motor assembly was clean from dust but it is excessively rusty. I am wondering if the condensation drain on the A/C that sits (4-5 ft above it) wouldn't be failing, causing the motor to fail/rust. I haven't seen the bearings yet but I wouldn't be surprised if they failed due to rust.

https://imgur.com/a/CsL3UHX


thank you

 

Do you have a second person for help ?
Hold the blower with the motor down and several inches from the counter.
Tap on the shaft with a block of wood and a hammer.
You don't want to peen the end of the shaft.

 

I don't but I can figure something out.
thank you

 

Got it out by tapping on the shaft with a brass tip while keeping the motor off the floor with spacers between floor and blower.

I tried powering the motor by itself (black/white) and nothing.
I'm not sure if I'll replace the whole motor or look for bearings after I disassemble it.

https://imgur.com/a/zrG8Goz

 

Really weird the bearings don't seem to be excessively out of whack but the motor would just hum regardless of the speed setting.
I'll order a replacement today.

 

I replaced the motor and everything is now working.
thanks for the help