Any HVAC Experts around? Have a wiring Question

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jmolayal

Senior member
Apr 21, 2001
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Cliffs: I'm pretty sure I've wired this new blower motor wrong. No fire, yet.. Sorry ATOT.

So I had some issues with the blower motor (note, not the condenser motor outside the house, the one inside) and had to change it out. Went to Johnstone supply and they gave me a new 1/2 HP motor with seven wires. The old unit was a 1/4 horse power with 5 wires. The guy told me to just wire it according to the affixed label, and this is what I came up with.

The Capacitor has 2 sides, (not 3) and is rated at 5 MFD.
On one side I have:
White (from furnace) and White from Motor

One the other side I have:
Brown and a Brown with white stripe.

Also I have

Red (from Furnace) --> (Red from Motor)
Black (from Furnace) --> Black with red stripe (from motor)

Also, the Yellow and the Blue Wires from the Motor are currently capped separately and not connected to anything.

Having wired this all up now, the blower kicks on and runs great for about 10 mins. Then it just.. Stops. Almost like it's going thermal and shutting off. There is a humming sound and nothing else. The motor also won't kick back on unless I let the whole thing sit off for 20 - 30 mins.

The whole thing also makes a hell of a lot of noise. The "squirrel cage" spins freely and doesn't make noise when spun by hand. Firing up the blower motor though, causes a loud racket.

The wiring diagram said use a 5 mfd Capacitor for 1/4 hp, and 7.5 to get a 10% stronger blower. The 1/2 version says to use a 10 mfd Cap.

Any ideas on what I've done wrong? I'd appreciate any advice.
 
T

texline

Junior Member
Nov 26, 2005
3
0
0
your replacement motor is known in the trade as a"rescue" motor, you did not say if your motor was 115 volt of 230 volt . it WILL make a difference. The brown wire and the brown wire with the white stripe, go to the capacitor, normaly the striped on to the cap "common" side. altho' on a 2 connection cap it realy does not make a difference. On a 115 volt system, The white from the motor should go to your "common" electrical connection, the other 4 colored wires are "speed tap" conductors, black usually being "high speed" red "low speed, and the other 2 are medium high and medium low speed. A couple of these colored wires will usually attach to a blower control relay or board on the furnace. Prob the black hi when in cooling mode, and on of the lower speeds in heating mode. your getting a back fed connection on the motor now, that's why its heating up and making a noise, it won't last long in that mode.......... Good luck, YMMV and all bets are off if it's a 230 volt motor
texline
 
D

drnickriviera

Platinum Member
Jan 30, 2001
2,443
250
136
If it's all wired correctly, then wrong size cap. It's hitting the thermal overload. go get a 10MFD and a new motor. I just ran into this a couple weeks ago due to a rubbed off sticker on the box. Dangit Drnick, read the motor nameplate next time. Double worse for me as it was 125F in the attic, and I had to change it twice. I got the motor running with the right size cap, but it only lasted 2 weeks before the motor went out
 
B

BUTCH1

Lifer
Jul 15, 2000
20,433
1,769
126
jmolayal said:
Cliffs: I'm pretty sure I've wired this new blower motor wrong. No fire, yet.. Sorry ATOT.

So I had some issues with the blower motor (note, not the condenser motor outside the house, the one inside) and had to change it out. Went to Johnstone supply and they gave me a new 1/2 HP motor with seven wires. The old unit was a 1/4 horse power with 5 wires. The guy told me to just wire it according to the affixed label, and this is what I came up with.

The Capacitor has 2 sides, (not 3) and is rated at 5 MFD.
On one side I have:
White (from furnace) and White from Motor

One the other side I have:
Brown and a Brown with white stripe.

Also I have

Red (from Furnace) --> (Red from Motor)
Black (from Furnace) --> Black with red stripe (from motor)

Also, the Yellow and the Blue Wires from the Motor are currently capped separately and not connected to anything.

Having wired this all up now, the blower kicks on and runs great for about 10 mins. Then it just.. Stops. Almost like it's going thermal and shutting off. There is a humming sound and nothing else. The motor also won't kick back on unless I let the whole thing sit off for 20 - 30 mins.

The whole thing also makes a hell of a lot of noise. The "squirrel cage" spins freely and doesn't make noise when spun by hand. Firing up the blower motor though, causes a loud racket.

The wiring diagram said use a 5 mfd Capacitor for 1/4 hp, and 7.5 to get a 10% stronger blower. The 1/2 version says to use a 10 mfd Cap.

Any ideas on what I've done wrong? I'd appreciate any advice.
Click to expand...

Sounds like a thermal event, if you wired it wrong probably wouldn't run at all, did you re-use the cap that was on the old motor or did the replacement come with one?, the motor plate should have the required Mfd.'s for it to run properly. As for the vibration make sure you didn't accidentally knock any balancing weights when you removed the old motor, that could cause vibration, since the motor is new you would have to assume it's bearings are good but give the output shaft a wiggle and see if there is any side to side play, Good luck, I hate F-ing around in the attic this time of year, it's brutal..
 
T

texline

Junior Member
Nov 26, 2005
3
0
0
Just tryn' to be helpful :)
I do HVAC for a livin' and have changed probably 50/60 condenser fan and blower fan motors the last couple of months...........
Main problem is 99% of replacement motors and capacitors nowdays come from China or India, some Mexico........... Quality control SUCKS......... Cheap tho' :)
As Forest would say "thats all I got to say about that"

texline
 
J

jmolayal

Senior member
Apr 21, 2001
405
0
76
Just wanted to let you guys know that I fixed it. Turns out that the two brown wires were on wrong. I needed on on each side of the capacitor instead of both on the same side.

Any recommendations on fan speed though. Should I ran it max speed for cooling and low speed for heat? Or would speeding up the heat speed be better?

Thanks for all the input

- Jaison
 
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