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airheatman, HVAC Technician
Category: HVAC
Satisfied Customers: 8168
Experience:  Furnace, A/C and heat pump specialist.
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How can I reduce the rpm of furnace blower motor on just one

Customer Question

How can I reduce the rpm of furnace blower motor on just one spd tap to reduce cfm. Motor has 3 spd taps but all are too much cfm for cooling coil. What a mess.
Submitted: 1 year ago.
Category: HVAC
Expert:  airheatman replied 1 year ago.

The 80,000 furnace is not designed to perform with a 2 ton system .This is a 3.5/4 ton furnace.

You will need a smaller furnace or will have to do some experimental rigging .You could try replacing the motor with a lower hp motor, but will have to make sure the amp draw does not exceed rating on new motor

Customer: replied 1 year ago.
I was thinking of maybe using choke coil on one winding to achieve this.
Expert:  airheatman replied 1 year ago.

Not sure how that would work.I a not familiar with doing this as a solution to slow down a 120v AC motor .Would you like me to open he question to see if other experts may know?

Customer: replied 1 year ago.
Not at this time.
Expert:  airheatman replied 1 year ago.

Ok good luck with this.If I can assist further, let me know.I would probably get one of those universal "trip saver " motors that adjustable from 1'8 to 1/3 hp motor and experiment with speeds to find a speed that will move air slow enough across coil to maintain at least 17 degree drop and amp draw stay within parameters.

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Customer: replied 1 year ago.
If I had a equivalent motor with 5 spd taps that would probably serve my customer but this one of those jobs where someone has sold equipment they had to sell not what the customer needed and I'm trying to clean it up for them as inexpensive as possible. I need to keep heating cfm as is though.Thanks again
Expert:  airheatman replied 1 year ago.

I am thinking about using the trip saver shown at link below.You can cut the spade clips off that go to the taps and wire nut the wires to different speed wires. Maybe use 1/5 for cool and 1/4 for heat if you need heat to move more air than cool.