Hi -

I have a 1987/88 Rheem furnace model # rgda-07ea-cr, 75,000 BTU, natural gas.

The blower motor is starting to get noisy and vibrate. I pulled it out and took it apart and looked at the bushing and shaft and see the shaft is wore, so thinking there is not use just replacing the bushing.

The Rheem part number on the motor is 51-21682-91 which I’m told is superseded by 51-23015-91.

The motor is a GE 1/8 hp, Model 5ksp29kk 1722s,2 spd, 1050 rpm, 5.1 amps, 5” body diameter, ½” shaft, 3 ¼” shaft length

It cross references on Grainger’s site to a Grainger # 4uu83, A.O. Smith 9703 fro $86.30 for a walk-in.

I believe my current motor has an external capacitor but the A.O. Smith motor from Grainger has an internal capacitor.

Are there any issues using an internal capacitor motor for a replacement? If so how hard is it is to convert from on to the other?

I can get the RHEEM 51-23015-91 motor with capacitor, which is a 1/5HP, 3 spd, for $103.00, is it worth the extra money to have it fit directly?

Any better/cheaper options out there?

Thanks a lot!

John

Buy any 5" universale motor with a capacitor rated for it. Just get the same voltage,HP and rotation the same. If the shaft is longer cut it off with a hacksaw.

If the motor uses the torsion-flex mounts that are screwed into the sides of the motor case, you better go with the OEM replacement. Drilling a motor case is risky business.

Used a belly band universal mount. It worked but was a pain to install.

I was planning on using the existing mount. It just has a strap clamp that goes around the middle of the motor with bolt and nut that tightens the clamp around the motor. 3 legs are clamped under the clamp ring against the motor. Each leg has a rubber grommet on the end that is attached to the outside of the squirrel fan cage with 3 machine screws.

Thanks again.

I was planning on using the existing mount

That will work OK but remember to reinstall exactly as removed and if the motor has oil holes or access points make sure to mount the holes in an upright position so oil can be dripped down the holes when lubricating. Some motors do not have oil holes and are permanently lubricated and in that case it makes no difference. Also check to make sure the little rubber mounts are still in good condition and that all metal spacers if so equipped are reinstalled into the center old the rubber mounts.

So here is an update on this, I switched my blower assembly with the one I pulled from my neighbors old furnace. My old motor was a 1/8 HP 2spd 1050 rpm. The one I swapped is a 1/4 hp 3 spd 1075 rpm. I think the blower assembly and fan are a little larger as well, more CFM's?

The new one is wired on low speed according to the wiring diagram.

The new one sounds a lot quieter than my old one at start up, and sounds like it is pushing a lot more air.

But, when the furnace starts the fan runs for a maybe around 40 seconds then stops for 20 seconds, and then starts again and runs fine the rest of the cycle. Maybe a couple times it done it more that once.

Do you think it could be cooling the plenum too fast and being shut off by the fan control, then when the plenum heats up, it kicks back on and is now warm enough to keep running.

Is what's happening with this dangerous. Should I switch it back? Is it possible that my neighbors furnace was a higher BTU and this fan is too much for my 75,000 BTU furnace? I did not check, but they sure looked the same.

Is there an adjustment for this? Does it hurt anything.

I looked at the fan limit switch. The setting for off/on are 90/130 and off is 230. I moved the 130 to the max which is 140. This seens to have solved the problem. Any harm in doing this?

Thanks! John

No as long as it works.

Nope. Motor in question is a shaded pole(SP) motor and does not have capacitive start. Use a general replacement SP motor such as a Fasco D178 should do the job well.

P.S. Shaded pole motors should never replace PSC type but OK for vice versa.