AC motor airco

[Kjelt]

Hi all,

i am more a digital microelectronics software type than a 230VAC mains AC motor type so I need some help.
I have a small airco that cools a room to 12 degrees C ,   24/7 52 weeks a year and after 8 years or so it now and than the fan starts to make loud whining noises. Sometimes it does this for hours so loud it gets us at night out of our sleep 
Than it is quiet again for sometimes days in a row.
So I called the firm who installed it and they can't really help me: the motor is "maintenance free" so they can not service or lube it. It can also not be replaced by them since they and the manufacturer no longer have it in stock.
So their only way out is to replace the entire system, which costs a lot of money 

The questions:
- what is the most plausible cause for the noises , it is AFAICS not ab obstruction in airflow, could it be the bearings, or ?
- is it possible to lube or clean the ac motor or bearings in any way it no longer makes these high pitched noises or is it maintenance free as claimed so replacing it with a new one the only solution?
- anyone know where to get replacement motors like this one or do I first need to unbox the whole thing for a manufacturer name, type ?

thanks already for the help   

[SeanB]

Manufacturrer and model of aircon for a start, as the motor could be one of 2 types. First would be a plain AC induction motor with capacitor, using either speed control via a triac or with speeds via taps on the motor. Other type is a DC brushless motor, most likely a 24VDC unit. Either one is rather generic, with the AC motor being very cheap, and the most common fault being a capacitor that is low in value. DC motor is more expensive, and the control method varies but most are DC voltage control with a feedback of rotation.

Most common cause though of a noise from the fan is the bearing opposite the motor, which is generally a sleeve bearing or a roller bearing running in a rubber housing. You take the filter off, undo the typically 3 screws holding the front cover on ( and often the screws holding the electric access cover, of course after the power is disconnected at the mains) and remove the front cover. Then you undo more screws and remove the condensate tray, and undo it from the tube ( typically it has a metal wire lock held with a screw) then clean the dirt from it. With that off then you remove the controller housing and boards so you can undo the motor screws and release the motor from the unit Then remove the fan unit and the bearing will be loose at the far end.

Clean the blower and remove the motor and lightly lubricate the connector, and put some light grease on the bearing inside, then put the kit back together. Then it will likely be silent for years again.

A quick temporary fix though is to take some spray oil, and use the long tube to get a little between the fan end and the bearing at the non motor end. That should stop the noise and prove it is the bearing.

[Kjelt]

Ok thanks a lot  that will be a nice task for one of the coming weekends.

It has no brand or model , this is the inside unit and it was custom build by the dutch firm that delivered the airco, the outside unit was also custom made but has a standard airco unit from Italy.
It is actually a special kind of cooler for a winecellar that cools to 12^oC and 80% moisture (where normal airco inside units would freeze up).
Hopefully I can get the outside off since they used a lot of rivets, it was a custom job. Thanks at least I now know there is an opportunity to fix it I will investigate further and get back when I get inside. 

[Kjelt]

I have been ill for over 3 weeks so haven't been able to start this but today I have started  .
I first dismounted all the surrounding plasterwork and was able to see now that it was not a custom job as they told me (or remember 12 years ago)
but that the evaporator is a standard Searle TG2-7.
I opened up the metal cover that keeps on hanging on its hinges since all the airco tubing goes through it in the back (can not remove totally),
but I had enough room to disconnect and remove the motor with fanblades 
I removed the fanblades and was able to see that it is a one phase 240VAC motor,
the manufacturer and type of the motor:
A.O. Smith
Ser 4NA UC16085
F Model type AB2N6259K 
240VAC 0,46A. see picture.

Unfortunately as you can see the top (and back) plates are fixed with rivets not with screws. So I have as a question, whats next?
How can I lubricate the bearings just put some oil or WD40 in it ? Or can I only replace it with a new one 

Another question: how can I make this motor run a bit more silent during the night, can I use a Variac to put 180VAC-200VAC on it during the night and switch with a relais
to 230VAC if the cooling starts? Or is it damaging for the motor to run on a lower voltage? Or any other circuits to do this?

Thanks all 

[Kjelt]

I see that the motor can be ordered new so that is hopefull but I rather lubricate this one and have it running again this weekend 
http://www.e-team-shop.de/oxid.php/sid/x/shp/oxbaseshop/cl/details/cnid/ea645be7f1e75e155.06737963/anid/4d351ee8dec73fc18.60897226/pgNr/3/Luefter-Motor-Fasco-Mod%3A-AB2N6259K-240V-50_60Hz-0.46A-211-015-104-Class-B/
http://ascateringsupplies.co.uk/part.aspx?pCode=ASC34250

[SeanB]

Those covers look like they are pressed on, so likely you can pop only the one off and have the motor apart to get to the bearings. You likely had a pair of long bolts that went through the entire motor, through those 2 square holes in the top and a corresponding pair at the bottom, so simply clamp the motor lightly in a vice ( lightly means it can still move) resting those lugs on the top of the vice, and use a drift to tap off one pressed steel end cap. Then you will have the bearings, and can pop off the steel cap if present or pull off the 2 6000 series metric bearings and get 2 new ones. Typically you want a 2RS version which has rubber seals on the ends so lasts longer, or just pop off the outer steel cover and repack with either NGLI1 grease or use some gearbox oil ( manual box not auto box, must be a SAE 90 or so, or a viscosity range from 450 to 630 heavy oil) then put back together, making sure to put all the spacers and shims back in the right order they came out, and place the cover on the same orientation it came off.

Done quite a few of these, and after a few they do work well afterwards. Even can be done to those horrid fans with sleeve bearings, though there a hammer to adjust clearances is needed.

[Seekonk]

WD40 is not oil.  It often "lubricates" by dissolving hardened grease near the location.  A thin oil would be best as it needs to wick into the scintered bearing, I often use automatic transmission fluid.  This often washes out debris and allows the shaft to bounce around creating new noises.  I have done this lots of times and the condition often comes back in 6 months to a year as the lube dissipates because it was never pulled up into the bearings. That motor will tap apart.  Use a screwdriver/chisel with hammer to tap on the sheet metal edge and keep rotating.  If the fan shaft is scored it can be polished but will likely vibrate  due to increased clearances. This fan motor is fairly generic in size.  Use what time you get to find a similar replacement that will mount with some adaptation.

[Kjelt]

SeanB thanks a lot for the assist, I do see a lot of english words I have no clue what they mean so please could you enter "beginners" mode for me an assist with it line for line so I don't end up with a broken motor  .

Those covers look like they are pressed on

With covers you mean the entire two black metal surroundings not only the small innerplate with 4 rivets, right?

You likely had a pair of long bolts that went through the entire motor, through those 2 square holes in the top and a corresponding pair at the bottom

correct I already took them out before the picture, this was where the motor was mounted with.

so simply clamp the motor lightly in a vice ( lightly means it can still move) resting those lugs on the top of the vice

I have a large wooden vice in the garage, so I have to clamp the vice around "lugs", what are the ''lugs" are these the 4 sticking out parts of the middle of the motor (the metallayers also used in transformers?)

and use a drift to tap off one pressed steel end cap

oops what is a drift some sort of flat metal like a screwdriver and i tap it at the side of the metal surroundings to remove it? Which one should you advise then the one where the axis sticks out and the fan is mounted (call that top one) or the other bottom one?

I stop for now to see if I got it right, sorry might be a bit frustrating for you as an expert but I never done this and english is not my first language and with technical terms I absolutely do not trust google translate (has cost me dearly in the past) 

Thanks 

[Kjelt]

WD40 is not oil.  It often "lubricates" by dissolving hardened grease near the location.  A thin oil would be best as it needs to wick into the scintered bearing, I often use automatic transmission fluid.  This often washes out debris and allows the shaft to bounce around creating new noises.  I have done this lots of times and the condition often comes back in 6 months to a year as the lube dissipates because it was never pulled up into the bearings.  This fan motor is fairly generic in size.  Use what time you get to find a similar replacement that will mount with some adaptation.

The problem here is also that the motor is mounted inverse so the axis where the fan is mounted is pointed to the ground which does not help putting oil on top since the gravity will just make it go the wrong way, but that is just a simple thought I have. But I can run it for 24hours standing up ofcourse before placing it back.

[Seekonk]

I edited up my last post before I saw new replies.  It doesn't take a lot of oil, more doesn't make it better. Inside some motors have a felt wick that stores oil and the back bearing generally has no access unless motor is taken apart.  A drift is a long round pin with a flat edge, chisel or screwdriver will do.  Rivets hold bearing assembly only.  Bolts hold the motor together long term, it easily comes apart. Run the motor for 24 hours then clean up and install.

[Kjelt]

Ok I understand (I think) and did the vice and slowly tapping the cover and it just fall off 
Now I am going into the city to see if I can find some oil that matches SeanB's description. Thanks all, to be continued.

[Kjelt]

Ah the whole axis comes out now beauty 
Running the bearings with my fingers see picture the left one turns 10 times before stopping so that one is pretty ok, the right one does not even turn half a round so that one is the culprit.
Just curious is it possible to replace that bearing. It seems like it is pretty stuck to the axis, do you need special tools to remove it? Or would you all suggest re-oilng and see if it can be made to spin again?

Thanks all. Very interesting. 

[SeanB]

The bearing is a press fit on the shaft, and they also have a steel sleeve over them to fit the housing ( looks like it originally used a different bearing so the steel spacers are fitted) so you place a large screwdriver either side between the bearing and the motor rotor, place on the wood vice so the screwdrivers are holding it then tap on the top of the shaft with a hammer ( preferably use a small socket that fits the shaft, likely a 11mm cheap chinese one you do not like, so it does not burr the end of the shaft) and the bearing will come off. Then the new one is put on till it is the same depth using a metal sleeve ( pipe piece) so you only hit on the inner race of the bearing so you do not damage it.

[Kjelt]

Ok thanks if I order a replacement I will try that  .

For now I have found ball bearing grease (they use it for bikes ball bearings) and I wonder how to get the grease inside the bearing between the balls?
It looks like it is almost completely sealed? 

[Ian.M]

*NEVER* pry (lever) between the armature core and the bearing.

You may want to try flushing the bearing with thinners, with the armature shaft down and the windings protected by foil to keep the thinners out of them, spinning the bearing vigorously to see if it frees off and if it does, then get it up to 100 deg C or so with a hair drier or temperature controlled hot air gun to drive out any remaining thinners (do it outside - fire risk!) then dunk the bearing while hot, still on the shaft into oil (types as suggested earlier) so it sucks some oil in as it cools as a short to medium term cure while you get the right bearings.

N.B.  If you apply too much axial pressure on the outer race, or hit one race while the other is fixed, it will trash any ball bearing by brinelling the bearing surfaces of the races.  This means that removal by supporting it on two screwdrivers and driving the shaft out should only be done if the bearing is totally FUBAR or a new bearing is available.   A puller that acts solely on the inner race wont brinell the bearing but an ordinary hook type puller that holds the outer race will.

[PA0PBZ]

( looks like it originally used a different bearing so the steel spacers are fitted)

It looks like there is some rubber between the bearings and the steel sleeve? Anyway, the bearings are very common NSK 608Z, you can buy them anywhere. They are used in skateboards, 3D printers, whatnot.

[Kjelt]

In the mean time I used a little bit of IPA on the bearings and they now run like new.
Now i probably have to regrease them, the ball bearing grease is to thick to get inside so I will go in to some carshop to find the manual gearbox oil to soak them in for awhile.

[BradC]

Just use clean motor oil, that will buy you some time (weeks/months). While it is working find a motor rewinding shop or auto electrician and then at a convenient time take the armature in and have them replace the bearings. They have the correct bearing pullers and presses and will have access to good quality bearings at the right price. Should not cost more than a few tens of dollars and maybe a sixpack of beer. Then it'll outlast the remainder of the A/C unit.

I did the bearings in an exhaust fan recently. They are about 30 years old. I soaked them in shellite (like a light lighter fluid) to get the old oil out and then soaked them in 10W30 synthetic motor oil. They are still a little noisy, but they run fine. I have replacements sitting on the shelf for when they finally fail or I get around to replacing them.

My policy now is whenever doing _any_ work on anything that contains a motor, I replace the bearings. Cheap insurance. Don't buy bearings on E-bay *ever*.

[SeanB]

That is why I love Bearing Man. They do decent bearings, seals and if they cannot supply a seal they will simply make it for you.

The bearing can be regreased by simply prising the cover off on the side that is away from the armature, so it has another cover in use. Careful as the bearing cage is right under that, so if you go too deep you break it or damage it ( same thing, it binds on the balls). then pack grease in and assemble without the cover, as the housing will do the same function for a long time.

You can buy bearings that are 2RS ( 2 sides rubber seal ) or 2S ( 2 sides steel dust cover) as well as 1RS ( one side only rubber), 1S ( one side steel dust cover) or even 0S for use in an oil bath and external seals. A lot of motors use a 1S or 1RS, as the other side will have a shaft seal in any case, and then they can put in a grease nipple for the bearings so you can put oil in the bearings during service. I replace gearbox bearings that have a 2S bearing with the 1S when it runs in oil, so the bearing gets better lubrication.

[BradC]

The bearing can be regreased by simply prising the cover off on the side that is away from the armature, so it has another cover in use. Careful as the bearing cage is right under that, so if you go too deep you break it or damage it ( same thing, it binds on the balls). then pack grease in and assemble without the cover, as the housing will do the same function for a long time.

Yes, but.... once the bearing is noisy then re-greasing is just prolonging the inevitable. The surfaces are already damaged, so it's not a matter of if it will fail but when. Bearings are cheap (relatively). Clean and grease(or oil) them to get you through the night, but replace at the next convenient opportunity.

[SeanB]

I have some machinery that uses a C3 tolerance high load bearing. New price for each is $1000 plus. Repacked with Molyslip grease a few years ago and it is still working, though I suppose at some point I will have to order a new set of bearings or the complete motor. Not any more noisy than new still, and a lot quieter as well.

[albert22]

This may help you:

A gear puller is needed. Try to borrow one or improvise a similar action. A last resort would be to split the bearing with a chisel by first denting it with a dremel. Be careful to not damage the shaft.
http://www.stu-offroad.com/axle/d44/d44-2.htm
When using the chisel do not hold the shaft just rest the bearing in a solid base like an anvil.
When installing the new bearing, note that the force is applied to the inner race. In this way no damage is done to the bearing.

[Seekonk]

That shaft end bearing is easy to press on at the factory.  Removing it is not so easy if you haven't had experience and some specialty tools.  It is easy to do a lot of damage.  Think long and hard before preceding. Pulling a dust cover and regreasing can buy a lot of time.  If serious about new bearings, put it back together and spin down the shaft diameter to remove any imperfections and make it slightly smaller.  No need to force the bearing the entire length.

[BradC]

I have some machinery that uses a C3 tolerance high load bearing. New price for each is $1000 plus. Repacked with Molyslip grease a few years ago and it is still working, though I suppose at some point I will have to order a new set of bearings or the complete motor. Not any more noisy than new still, and a lot quieter as well.

Yes, but had they come to a screaming, vibrating halt before you re-packed them?

[SeanB]

No, just noisy more than the new sound, so I was looking to replace, then got the price so decided to repack with moly grease. They shut up immediately, either just from having more grease or from the moly additive. Other gearboxes also got the additive, which did make them run a lot cooler and quieter. It did tend to foam the oil though, which was good to actually lubricate the top end bearings a lot better than splash lube. Still had to eventually pull it to replace main bearings, they got to the point where they killed the main seals and I had to pull it to get them changed as I do not have a puller that big. Fun lowering that 80kg motor off the box then unmounting the 150kg box off the shaft. I drilled into the concrete ceiling and installed a 2 ton hook eye and rawlbolt using epoxy for added strength. Chain block is great.