[threeonesix]

Last night my AC stopped working. No air was coming out of the vents. Earlier in the night I had noticed a whining sound every once in a while emanating from my mechanical room. I have a lot of computers in the next room as well so I wasn't sure if the noise was coming from one of them or not. As I was listening more closely, a loud, final screech came from my furnace in the next room. I immediately turned off the AC at the thermostat and also tripped the breaker to OFF. I opened the furnace and removed the fan/motor unit. I tripped the breaker back to ON, turned the AC fan to ON at the thermostat, walked back downstairs and listened to the blower motor. The fan was not turning in the squirrel cage and the motor was making a humming sound. Figuring this was the source of my problem I went ahead and turned everything back off, removing power to the furnace and disassembled the fan/blower unit so that I could take the motor in for replacement this morning. I also replaced the capacitor. Everything seemingly went very smooth.

The old motor was an Emerson 3-speed K55HXJYZ-5490. The new motor is a GE 5KCP39FGM421 2-speed. I have no idea if this is the proper replacement, and I am beginning to wonder if the guy at the wholesale supply place does either. I can't get the new motor to power on. I replaced the capacitor first. From the new motor I:

- connected the brown and brown/white wires to the capacitor
- connected the black wire to the black feed from the furnace (same as with the Emerson)
- connected the white wire marked as "LINE" on the GE wiring schematic to the red wire from the furnace (blue wire on Emerson was connected to this red wire)
- used a plastic cap to close the red wire from the GE motor (the red wire on the Emerson was also capped this way)
- connected the white wire from the furnace to the capacitor

After connecting all of the wiring I closed up the wiring box and put the blower/fan unit back in its housing at the bottom of my furnace. I tripped the breaker back to ON, set the thermostat to a low temperature and flipped the fan control to ON. I expected the blower to come back on immediately. It did not. I returned to the mechanical room and could hear a light buzzing emanating from the furnace (not from the blower motor area but up above that, near the heat exchanger). I waited 10 minutes but the blower never kicked on. I could hear the AC unit outside my house working.

Thinking maybe I had the wiring incorrect I swapped places between the red and white wires coming from the GE motor, connecting the GE red to the furnace red and capping off the GE white so that it was not connected to anything. Still nothing came on.

What could be the problem? Surely its not a bad board. I don't even see what looks like a motherboard anywhere. I do see a closed metal box from where it appears all of the furnace wires emanate. I'm guessing that's the board. It's just that considering I heard all this noise before the AC stopped, I'm pretty sure the problem is the blower motor not the board. I've heard these types of motors seize before (used to work in a motorcycle shop) and that is what this sounded like.

Images:

Old Emerson wires

Old Emerson wire connections to furnace inside wiring box:

What may or may not contain the "board":

Old capacitor from top:

New GE motor box label:

New GE motor wiring schematic:

Some Honeywell unit in the furnace:

Old Emerson motor wiring connections to furnace:

 

[JJboy]

- connected the brown and brown/white wires to the capacitor Correct

- connected the black wire to the black feed from the furnace (same as with the Emerson) Correct

- connected the white wire marked as "LINE" on the GE wiring schematic to the red wire from the furnace (blue wire on Emerson was connected to this red wire) Wires color means difference speed

- used a plastic cap to close the red wire from the GE motor (the red wire on the Emerson was also capped this way) Correct

- connected the white wire from the furnace to the capacitor - You don't need this connection. You already connected brown and brown/white wires to the capacitor

 

[threeonesix]

I tried removing the white wire from the furnace from connecting to the capacitor and it didn't have any effect. I'm going to try using the old capacitor and see if that makes a difference. I doubt it, I'm sure something else is wrong but I have no idea what. Would be nice to know what speed was provided by the blue wire from the Emerson motor. I couldn't tell you if the blower previously used only one speed or two. I'd almost guess one, because there was no difference in the amount of air coming out of my vents between summer and winter.

Thanks for the ideas!

 

[threeonesix]

Just figured it out. Had the brown and brown/white wires connected to the capacitor switched. Swapped places with those and the blower came right on after power was restored. Now I feel stupid.

Again, thank you for the help!

 

[JJboy]

Black-High Speed - Used to cooling mode
Blue-Med Speed - Used to heat mode
Red-Low Speed - Used to heat mode

:thumbsup:

 

[threeonesix]

Thanks, that's what I figured. So, odds are I should leave the red wire from the motor, which the motor reports as "low" speed, connected to the red wire from the furnace feed, and leave the white wire from the motor, which it doesn't show as any speed, disconnected and capped, correct?

 

[Marty S.]

The white is neutral as in all 120v circuits have a hot leg and a neutral leg. Wire nut the old white to the new white. Which brown goes to which post on the capacitor does not matter. One speed is for heating and one is for cooling and your furnace uses both.

 

[threeonesix]

Looking through some paperwork the previous homeowners left I located the installation & operation manual for the furnace. It confirmed for me that the red wire from the motor feed needs to be connected to the red wire from the furnace feed in order to operate the heat when a 2-speed motor is used. Whew! Problem solved and I'm putting this case to bed! Beer time!

 

[REP]

I don't get it,where did you end up putting thre white wire??????????

 

[threeonesix]

I don't get it,where did you end up putting thre white wire??????????

I capped it with a plastic cap and left it alone. It is not connected to anything. Seems odd but its working so I'm guessing it either doesn't need to be connected to anything or my house is about to burn down. Hopefully the former.

 

[REP]

There is something missing here.
One it shouldn't mastter which brown wire is attached to which capacitor tab.
Two how can a motor run without a common?
I don't know what you have there,but it is not what the diagram shows in your picture.

 

[threeonesix]

There is something missing here.
One it shouldn't mastter which brown wire is attached to which capacitor tab.
Two how can a motor run without a common?
I don't know what you have there,but it is not what the diagram shows in your picture.

I agree that it shouldn't matter. So did my friend Mike, an HVAC technician. He was every bit as surprised as me when he swapped the brown wires on the capacitor last night and the motor would not turn on. Swapping them back again resulted in normal functionality. He also found it mystifying why the motor was working with the white common wire not connected to anything. I don't know what to say, other than my house was 74 degrees this morning and 94 degrees yesterday afternoon, so I am a happy homeowner. Unless it is now burning to the ground.

As far as the diagram (pink thing) goes, the only thing that isn't exactly as shown there is that the white common wire is not connected to anything. Otherwise, black-to-black, red-to-red results in perfect operation of the blower/furnace/heat/AC.

 

[beenthere]

There is something missing here.
One it shouldn't mastter which brown wire is attached to which capacitor tab.
Two how can a motor run without a common?
I don't know what you have there,but it is not what the diagram shows in your picture.

He has the common connected. Good chance one of the 3 wires on the cap was loose when he first tried to run it.