Furnace blower motor replacement

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Old 02-09-16, 07:38 AM
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Furnace blower motor replacement

My Conquest 90 furnace blower motor died on me.

Ordered an equivalent motor and a new replacement capacitor.

Old motor : GE Brand, 1/2hp, 7.5uF/370V cap, 6.3A, 115V, 3 speed

New motor: Protech Brand, 1/6hp-1/2hp, capacitor varies based on hp, 5.8A, 115V, 4 speed.

1) The new motor chart states that at 1/2hp, the capacitor should be 10uF. With a 7.5uF capacitor, the hp would actually be 1/3 hp according to the chart. Should I upgrade to a 10uF capacitor or stick with a 7.5uF capacitor, which is what the original motor had.

2) The new motor is 4 speed (low, med low, med high, high), the old one was 3 speed (low, med, high). Which wire should I cap off, the med-high or the medium-low?

Thanks in advance for the help!
 
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Old 02-09-16, 08:11 AM
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I'd use the 10uf. If the cage was designed for 1/2 horse motor you will likely overheat at 1/3HP.

With the exact model number you can look up what the original blower speeds were and then choose the taps to get as close to those as possible.
 
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Old 02-09-16, 09:12 AM
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I would cap off Low and High.
 
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Old 02-09-16, 05:09 PM
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Got the 10uF capacitor.

After running the furnace for over an hour, put my hand on the motor and it was hot. Not too hot to touch but hot. I could keep my hand on it indefinitely but barely. Is that normal or do I have another issue that cause my original motor to fail?
 
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Old 02-09-16, 05:34 PM
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It's really hard to say how hot is too hot as motors today run hotter than they used to.
What speed is it running at ?
 
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Old 02-09-16, 06:01 PM
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Right now heat is running on medium-high. With the old motor, which was 3 speed, it was running on medium.

Should I try medium-low (which is taped off right now)?
 
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Old 02-09-16, 06:07 PM
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I never really understood the using of multiple capacitors to change rated horsepower. Basically the larger cap is causing that motor to work harder and run harder.

Personally.... I'd try the 7.5uf cap in there and see how it performs.
 
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Old 02-09-16, 06:17 PM
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If you can leave your hand on it, but just, then it's around 55 degrees C. (DAMHIKT) It would not be unusual for a motor to run at that temperature. Doesn't mean there isn't a problem, but if the bearings spin freely and the blowers not all loaded up with gunk or the airflow restricted, there's not a lot else to cause it run hot, short of it being underpowered. It's easy to make a motor that runs cooler, but it adds cost and, well, you know how that goes....
 
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