How to replace 2-speed blower motor with single speed

Problems related to residential installations.

How to replace 2-speed blower motor with single speed

Postby vfp9guy1 » Sat Dec 08, 2012 6:31 pm

Hi, I have an older Lennox furnace. The previous homeowner had a Honeywell electronic filter and therefore a 2-speed motor with the low speed constantly running and the high speed controlled after the flame ignites. The current motor is a GE 5J771GS1 and it just died today. That motor is 1/3 - 1/15 hp with speeds of 1725/850. I can't find one here in Vancouver, but I can get a similar motor (5793C) 1/3 - 1/8 hp with speeds 1725/1200. Before I buy that one (expensive > $300), can I use a single speed motor instead (and forget about the constant lowspeed running) because we have disabled the Honeywell and don't need constant running. If so, what connection differences do I use? The current motor has 3 wires plus ground, but they have been spliced and are not color-coded. Also if yes, should it still be a 1/3 hp ? Thanks in advance
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- How to replace * blower motor with single speed

Postby vfp9guy1 » Sat Dec 08, 2012 6:38 pm

Sorry about the 1st post but the posting dropped my numeric values ... probably because of hyphens or slashes... here is a revised text.
Hi, I have an older Lennox furnace. The previous homeowner had a Honeywell electronic filter and therefore a two speed motor with the low speed constantly running and the high speed controlled after the flame ignites. The current motor is a GE 5J771GS1 and it just died today. That motor is one third and one fifteenth hp with speeds of 1725 and 850. I can't find one here in Vancouver, but I can get a similar motor (5793C) one third and one eighth hp with speeds of 1750 and 1200. Before I buy that one (expensive > $300), can I use a single speed motor instead (and forget about the constant lowspeed running) because we have disabled the Honeywell and don't need constant running. If so, what connection differences do I change. The current motor has 3 wires plus ground, but they have been spliced and are not color coded. Also if yes, should it still be a one third hp. Thanks in advance
vfp9guy1
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- How to replace * blower motor with single speed

Postby Freon » Sun Dec 09, 2012 12:41 pm

I assume the old motor is a PSC motor. Most have 3 speeds as you know already. For your intended use, one speed is fine and the only requirement is that the speed be high enough to provide the correct air flow thru the furnace heat exchanger. Usually the middle speed is the one used for heating so you'll need to determine the rpm for the middle speed because the new motor will need to give you that rpm. The installation manual for the furnace should have all the air flow data you need to choose the correct motor. And yes, you'll want a one third hp motor.
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