Lennox blower issue

mattmia2

I have a lennox g32q-75-2 2 stage direct vent gas furnace.  The blower is making a loping sort of beat liek noise.  It only does it on low.  Is there anything other than a bad blower motor that this could be?  There aren't just some bad rubber bushings or something, are thre?  I replaced the capacitor around 5 years ago when the motor failed to start.  It is a capacitor run motor.  I tested the capacitor by measuring the voltage across it and current through it and the calculate capacitance matched the value of the cap.
You can hear the issue in this video:
https://youtu.be/HspVAAPTA3o

The current motor is nominally 1075 rpm and 4 speed.  I can get a ball bearing 4 speed motor that is 1200 rpm.  Will this small difference in speed make a difference in performance?  I can get a 4 speed 1075 rpm motor with sleeve bearings but since the bearings seem to be failing in this motor I would rather go with a ball bearing motor.

retiredguy

Did you check the amperage draw of that motor, make sure that it is turning in the right direction, see how much end play there is, check for worn bearings, and check to make sure that there is nothing in the blower wheel. It sounds as if there may be issues with the motor itself.

WMno57

Had a similar issue. The crimped together blower wheel was rotating within itself. Drove me nuts, until I finally saw the swarf and debris from where the rim would rub on the hub. It was only moving back and forth a couple of degrees, the shiny spots where it was crimped together gave it away.
Had a new wheel from www.supplyhouse.com in two days.

EBEBRATT-Ed

I am assuming this is a direct drive motor. I would stop the fan and grasp the hub see how much end play you have and also pull the shaft up and down horizontally and feel for play.

Then spin the fan by hand and listen for noise. usually one of those three things will let you know if the motor is going

mattmia2

It is direct drive. And maybe some slightly custom Lenox part.

I can't feel any endplay or side play on the shaft, it is in the realm where I would have to get the dial indicator to measure it. I'll measure current over the weekend. If I pull out the blower I will be able to better feel if anything feels weird. When this first started it was less severe and I cleaned each fin of the blower with a round brush. I didn't notice anything rough in the bearing then. It is a little hard to tell just feeling in with fingertips without pulling the blower out. I didn't notice anything where it looked like the hub or any other part was loose or bent but I'll take another look. I helped a friend with a blower making noise and the blower wheel just fell apart when I touched it.

ratio

You don't need a micrometer, these things aren't exactly precise. If you don't feel any motion lifting the wheel up with your fingers, that test passes. Look carefully for stress fractures if you think it might be out of balance.

A 1075 RPM motor is the same as a 1200 RPM motor—one is the synchronous speed (1200), the other has the slip figured in. I hear that comparing amps gives you a better match that just comparing horsepower, makes sense to me.

EBEBRATT-Ed

Yes, OEMs rate their motors funny sometimes with inflated horsepower. The old rule is never repace a motor with an amp rating less than the old motor and that always works. Maybe the blower wheel is out of balance or on it's way out. Maybe something got sucked into the wheel

mattmia2

ratio said:

You don't need a micrometer, these things aren't exactly precise. If you don't feel any motion lifting the wheel up with your fingers, that test passes. Look carefully for stress fractures if you think it might be out of balance.<</p>

By saying i'd need a dial indicator I mean I didn't notice any appreciable movement. I've seen blowers with like 1/4" of endplay that seemed to work just fine. I don't think it is out of balance, it only seems to be a problem at low speed, on high heat or AC I never noticed a problem(the control runs low for a fan call without Y). I do notice that the whole motor moves on some sort of resilient bushings but not with a fair bit of force.

ratio said:

A 1075 RPM motor is the same as a 1200 RPM motor—one is the synchronous speed (1200), the other has the slip figured in. I hear that comparing amps gives you a better match that just comparing horsepower, makes sense to me.

I was wondering how making a 1200 rpm induction motor with a 60 hz ac line was possible.

The motor does have a nameplate on it, it is just someplace where I can't see it without disassembling a good portion of the blower. I will to that this weekend.

It looks like virtually all of the north american motor manufacturers have been acquired by REGAL REXNORD so no matter what brand you buy you are really buying from them.(I still am not sure if Dayton is actually a manufacturer or if they are just rebranded for Grainger).

mattmia2

Ojk, it is the motor. Once I pulled the blower out of the cabinet I was able to feel a ton of up and down side play and some end play but no front to back side play so it is the bearings.

It is a 4 wing mount but the wings aren't evenly spaced. Is there a clamp on bracket with this odd spacing for a standard motor or do I need to get the Lennox part? It is a 4 speed 1075 rpm 1/3 HP motor.

I measured the current. It was about 4.2-4.5 a on low and 6 a on high. The ratings plate of the motor
says 5.1a.

EBEBRATT-Ed

I am sure you can get it from Lennox but any good HVAC supply house should be able to fix you up. There are a lot of aftermarket mounting clamps. Did you check Supply house.com? See the attached they have some Lennox OEM motors

mattmia2

With some careful drawing it looks like it is a 10.18" bolt circle tri wing mount with an extra arm, so a standard evenly space tri wing mount motor or adapter should fit. The lennox replacement is a tri wing sleeve bearing motor for about 3x the price of a similar motor without a lennox label next to the manufacturer's label.

pecmsg

Unless you have experience with aftermarket parts get the Lennox motor.

mattmia2

So it does indeed mount with a 3 arm 10.18" bolt circle. The housing has some extra holes with inserts and others without so you likely could use multiple mounting methods.



This was the original motor:


I replaced it with this motor with a factory tri wing mount, but i could have used a tri wing bellyband clamp too:


I forgot to take a picture before I re-mounted the blower:


I tested it at both low and high fire and the rise was within the rating plate specs. It got to almost 80 in the house running it at high for 10 minutes so it is almost certainly really oversized.

It is a lot quieter now, I never hear it running on low fire and now I can hear the whistling from the leaks around the blower door when it is running.

This is what the shaft under the old bearing looked like. I guess I'm not replacing the sleeve bearing and keeping it as a spare:


I guess I should clean this up sometime. somehow the common power to the t-stat was lost in moving the control board out of the way and back. The wire nut with all the commons seemed to have everything tight. Seems loosening then tightening and adjusting the common terminal got it working again, maybe some of the insulation was under the screw.

pecmsg

Did you amp out the replacement?

mattmia2

Alright, so here it goes. Either I found an issue with how the furnace was installed initially with ESP that is out of spec or Lennox fudges the motor size knowing that there is a lot of airflow when it is at high and it isn't going to overheat.

The old motor drew a little over 6 a on high with the blower door off. It drew about 4 a on low. It claims 5.1 on the ratings plate. The new motor draws a little over 3 a on low and about 5 a on high with the blower door in place and has a nameplate rating or 4.15 a. After running the motor on high for 10 minutes it was just warm, not anywhere in the realm of too hot to touch.

mattmia2

I'll give you one guess which direction the excessive play is in:

EBEBRATT-Ed

Checking the amps with the blower door off can overload the motor....it's trying to gobble up all the air it can with no return duct restriction.

So if I understand what you posted the new motor is over amp on high with the blower door in place.

Look at my post of 1/12 the OEMs rate their motors funny. They cheat. Thats why I said when you replace a motor especially an OEM motor you have to go by amps the horsepower means nothing.

This is very common they do it on a regular basis.

Can you run on a lower speed and still not exceed the furnace temperature rise and still get enough air flow?? Or do you have AC and need high speed??

Some motor mfgs will let you run service factor amps but not your new one it has a 1.0 sf

mattmia2

Do you mean rating plate current or measured current?

I need high speed for ac. uses low and med-high for heating on low and high stage.
It is about a 5% difference with the door on or off with the new motor so i'm pretty sure it was drawing about 20% more than the ratings plate with the old motor even with the door on

wmgeorge

Did you replace the capacitor with the new motor also? Motors vary as too what size needed. The door needs to be in place and also the correct filter.

mattmia2

Yeah, i replaced the cap. the old motor wanted a 5 mfd, the new motor wanted a 10 mfd. The old cap was only a couple years old.

EBEBRATT-Ed

@mattmia2

I will give you an example. We replaced a huge cooling tower one about 10 years ago. It was a direct replacement meaning the new tower matched the old no repiping.

The old tower had 3 30 HP 480volt motors 3 phase. I don't remember the amps but is was about 35-40


The new tower shows up exact same tower and it had 3 30hp motors...according to the motor name plate.

But the "new motors" were rated like 55 amps each. How can this be??

This was going to require 1000 feet of new wire, maybe replacing conduit, disconnects and motor starters etc.

They were Marathon motors so I called Marathon in TN.

Guy tells mee "those are OEM motors they are really 50 hp motors labeled as 30 hp motors and it's all legal, we can put on a motor whatever we want"

Needless to say we bitched and complained and refused to pay for the towers until they sent a guy up from the factory and he changed all three motors.

This is common practice in the HVAC industry. I do not know how they get away with this but they do it all the time. Carrier is a big ofender but they are not alone. I think they do it so everyone will buy the replacement motors from them. Apparently they can label the hP anything they want but have to put the correct amps on it

I was told 46 years ago size the replacement based on amps you can't trust the hp rating.

mattmia2

So interestingly the catalog shows that motor as 4.5 a and says that all 1/3 hp 1075 rmp motors are 1.35 service factor. I think there is a lot of hey we already have these parts of a motor, lets put them together and fudge the ratings to this marketing objective. I would have gone with the 1/2 hp but the one with the integral 3 wing mount that was 4 speed didn't show up in their online catalog search and I was concerned about the customized controls in the furnace having relays that could handle the higher starting current.(it looks like they have marginally sized relays that do the speed selection but a 1hp rated relay that is supposed to to the on/off switching.)

EBEBRATT-Ed

I could never understand how the OEM can play with the motor HP like they do. It doesn't seem right but I have seen this for years and all the MFGs do this.

I think it is a ploy to get people to buy OEM parts

mattmia2

There are a couple of re-rating options available in the customization section of their catalog.