Tip & How-To about AO Smith Rheem - Rudd Furnace Motor 51-21853-01 1/6 hp 1075 RPM 208-230V

Replacing a heaters blower motor

The indoor blower motor is powered by 115 volts or 230 volts, either way it wires the same.
Every motor be it a single speed or multiple speed will get the 2 legs or power,
Line 1 and Line 2 or L1 and L2 to make it easy.
Common always gets a leg all to itself, you cannot run both legs of power to the speeds as the speeds are on the Run winding, that is a direct short, and you cant run a leg to Start or it will turn backwards! This is how we unlock compressor's that get stuck!
1 leg or power ALWAYS goes to Common.
The remaining leg of power, say it is L2, it goes to the speed desired or if a single speed motor, it can go to the terminal on the Run capacitor that is wired to the Run winding, A Run capacitors terminals are Run and Start.
Note the capacitors leads coming from the motor are both brown, 1 has a white stripe
the capacitors leads are obvious in that respect as well as being the only 2 leads that have female type ends that are for sliding over the run capacitors terminals, it does not matter which lead goes to what terminal as long as both get their own.
The remaining leg of power we are calling L2 will be going to the speeds desired,
Cool uses High while Heat uses Low speed, High speed is controlled by a fan relay or fan board on the high speed terminal or cool.
While the low speed is controlled via temperature delay, time delay or a fan board on the low speed terminal or heat.
There is no need to get an exact replacement motor, as long as the shaft diameter, frame size, rotation, voltage & HP rating equal or better,
(you can go bigger HP, never smaller) you will be ok.
Some universal or trip saver motors have bushings for various shaft sizes, and an ability to reverse rotation by inverting a plugged set of leads. Belly bands are used for most applications so even if your OEM motor has built in motor mounts there is a belly band that can be used to replace that motor perhaps cheaper if not faster, some OEM motors can be days away from being available

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1 Answer

I have a 1/2 horsepower electric motor 230 volt 3 speed w/ capacitor HVAC fan assembly. how do I wire it to power by color coded wires?

Keeping in mind that some motors may be different
The most common wire colors on a 3 speed motor are as follows:
Red- Low speed
Blue- Medium speed
Black- High speed
Brown capacitor wires ( usually two of them connect to the two capacitor terminals doesn't matter which wire to which terminal)
White - Neutral wire on 115 volt systems or the other 115 volt side of a 230 volt system ( note on a 230 volt motor this wire may not be white). Remember this is the most common wiring but different motors may have different wiring.
Hope this helps.


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I would suggest taking a closer look at the motor name plate. I am not familiar with a 120/240 three phase service. When I checked the web it shows: Voltage 115/230 (that is single phase), Max Amps 115 Volts = 19.2 Max Amps 230 Volts = 9.6 , Single Speed, Square Flange, RPM = 3450, Threaded Shaft, Frame = 48Y Used on the following models: Sta-Rite Max-E-Glas, Max-E-Glas II, Dura-Glas, Dura-Glas II, Dyna-Glas, Dyna-Max Pentair Whisperflow, Pinnacle and Anthony AR2 Series. You should also show what voltage you are connected to.

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On 230 volts you have 3 wires 2 are 115 volt and the third wire is ground. As long as you hook the ground wires together correctly the other wires don't matter. Usually the ground wire is either white or green. The black wires are hot (115 volts).

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L1 and L2 are the posts to hook up to, there is no polarity so either way works,

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1 Answer

I wish to rewire a single phase electric motor with compositor's that is currently setup for 230 VAC to 115 VAC. The motor is a Ingersoll-Rand Air Compressor motor with the following nomenclacher. Single phase RPM: 3450 Volts: 115/230 Amp.: 15/7.5 60 hz PN: 97264097 SN: BH87

The motor itself should have a sticker which describes the wiring for 115. It is a small change involving a single wire moving from one pole to another inside the motor starter cap (the bump on the motor itself).

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