Pulley Size

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Pulley Size

Postby lusty » Wed Feb 20, 2013 8:32 pm

Hey all,

I recently replaced my blower motor with a newer one, this one is a 1/2 HP 1725rpm single stage (It doesn't appear to have low or high it just goes one speed. The old one had Low/Mid/Hi speeds). I have noticed I don't get a lot of air flow coming out of the vents like with the old motor. I have cleaned the furnace, checked the ducts, and the airflow is still less than ideal. I'm curious if I can change pulleys on the blower unit itself to make it spin faster.

Currently the motor has a 4" pulley, and the blower has a 7" pulley on it, with a 17" belt. Could I put a 5" pulley on the blower unit? I was doing some math with and I'm getting 985rpm with that setup (I think? I'm not a engineer and my math skills suck). Would it make a difference?

I've read of other people changing pulleys without an issue. I don't want to overstress the motor or blow it up, as I just bought it.

Any info would be great.
lusty
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- Pulley Size

Postby Freon » Wed Feb 20, 2013 11:11 pm

Do not use dashes, slashes or question marks due to deletion.

What was the horsepower of the old motor.
What was the rpm of the old motor.
What diameter pulley did the old motor have.
Freon
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- Pulley Size

Postby lusty » Thu Feb 21, 2013 1:43 am

Hi,

sorry I didn't know about the deletion of slashes and such.

I don't have the old motor, I wish I did. I remember it had a hi med low on it, maybe it was three quarter horsepower but I am not sure. Sorry. Not sure on rpm either. We took it to the furnace store and they gave us one they said would work. I'm wondering if they messed up.

The pulley on the original I just took off and put it on the new one. It didn't come with one. It is 4 inches in diameter.
lusty
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- Pulley Size

Postby Freon » Thu Feb 21, 2013 12:38 pm

Without specific data you will have to go with trial and error. As you noted, the risk is overloading the motor and causing it to over heat. Try a 5" pulley and watch the motor for signs of over heating. Keep a hand on the case so you can feel the temperature. The motor should have a thermal safety if the case gets too hot.
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