small display cabinet keeps seizing up CF motors

Hi, I've got a problem with an old cabinet, it's really old and about 300L capacity.
The condenser fan motor bearings keep seizing up annually.
It's an old r12 unit on r134a, done before I worked there. The condenser is bottom mount under the cabinet, it has no fan cowling and air off it pretty much goes outwards from the fan, instead of flowing backwards and out the vents.
There was a lot of hot air being recycled because of this and it's mounting under the cabinet. So I packed up the gaps beteen the cabinet and condenser so less air was being recycled.
The only problem is the high air of from the condenser, it's about 55C, while the unit in it a 20C air conditioned space.
The fan motor gets no benefit of airflow due to the air being pulled off the fan to the sides because of lack of cowling and fan design, so the fan case is constant 50C+.
Now to me, that's probably causing the fan motor bearing failures every year.
But I'm not sure if it's just an airflow propblem or it may be a refrigerant problem causing exceess condensing temperatures.
Problems:
1) This customer can't spend money replacing equipment, the business owners (500km away) won't authorise it. But they do need everything working so he can give us money for repairs. It's taken us two years to convince them to upgrade their main a/c (looking at a 50k job here, so I don't want to piss him off either.
2) this is a really old cabinet, if it worked for 30 years on r12 without a cowling around the fan, I can't say it needs one to work.
3) I can't say just to get it reclaimed and recharged on a whim without having definite answers why, this guy spots bull**** a mile away. He's been managing hotels and shops for a while, he knows what he's got to work with is ****, but he doesn't have much say in it either. He's gone through a lot of refrig companies to find us, and he's staying with us because he thinks I know what I'm doing :).
So any ideas what to look for, as cabinet temps and all pressures look OK except for the cond temp. The fan is going the right way, condenser is clean etc.

The condenser may look clean, but can you see through it?

In my experience when the fan flicks air out to the sides the coil is blocked... and you mentioned that the cond temp is not ok, does that mean it's high??

Quote:

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Originally Posted by paul_h

So any ideas what to look for, as cabinet temps and all pressures look OK except for the cond temp. The fan is going the right way, condenser is clean etc.

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The motors use a small oil soaked pad that is in contact with the bearings.
If this pad dries out then the bearing siezes up a short while after.
This is normally caused be overheating.
If the motor is undersized eg 7 watt instead of 16watt then it will struggle.
Ensure you fit the largest motor and blade possible, most universal fit cond motors come in various sizes.
Do check the cond is totaly clean but I would check the motor.

taz.

I blasted through the condenser with nitrogen last repair, the coil is clear, not just looks clear.
As far as what your are saying taz, yes, that's what I'm getting at, the air off and the whole general area under the cabinet is too hot, and that's what I think is killing the bearings. The motor is by no means a small one, it's one that is normally fitted to much larger units than this one. It's a fasco 50D if that means anything, two of these will do a small coolroom condenser, and this is only a small display cabinet in an airconditioned space. It also is a ball bearing type motor, not a sleeve bearing.

I've been using NTN 608ZZ bearings as a replacement in Fasco 50D series fans I was told by the Bearing supplier that the ZZ has a better lubricant in it anyway they have been giving me a good run .I always date the back of the fan when I change bearings and 20 months is the shortest run time I've had that was on a old display sounding similar to yours.Could it be that the insulation is getting sad and the units running longer than normal also some of the old buggers hade a 50D 501 motor changing them up to a 50D 503 reduces the motor load making them run cooler.

How odd, I just came across this thread. I was at some medical equipment training recently and a manufacture said that there motors are seizing up. Even with a spotless condenser. Here is what they said. " The grease" is melting inside the housing under load. Well that means that when it's warm it runs all the oil or grease onto the bottom of the condenser pad. They said out of warranty try a different manufacture for that motor. It was a Fasco motor.:)

Hi Paul H ,
Quick Reply - Sounds like the Original R12 Condensor is underszed for R134A duty - ( Usually requires an additional MINIMUM of 15 % condensing capacity ).
The signs are present - Increased k TD , and pressures too i would'nt be suprised.If the compressors original , it wll have a high discharge valve wear rate under the conditions you mention.Cheapest option to get off the merry go round of circumstance you describe would be to fit a new R134A condensing unit , Which should also give the owner a warranty period.55 deg Air off + motor temp rise factor = very hot bearings in excess of original R12 operating conditions.Alteratively as another poster suggested - fit largest size motor & blade you can fit in - BUT remember you are trying to overcome a basic that should have been attended to pre your time on this site.

what is the fan blade made out of? if its the original and made of metal change it for a aluminium type

Hi Paul,

I am in agreement with most of what has been said here, but at the same time I realise your predicament of financial constraint.

Couple of inexpensive things you might want to consider.
http://www.refrigeration-engineer.co...ons/icon14.gif If not already fitted, try a new aluminium fan blade with a curved blade surface and greater pitch angle to obtain more air movement over the motor itself
http://www.refrigeration-engineer.co...ons/icon14.gif Make a cowling from an old cardboard box and some duct tape/cable ties
http://www.refrigeration-engineer.co...ons/icon14.gif However, if you still think or suspect that there may be air in the system, (I do from what you have said) and if the unit has a discharge or liquid service valve, Get your normal running head pressure figure and then disconnect the electrics to the compressor leaving the fan running. You should see a steady drop of your standing head pressure. When the air off the condenser drops to room temp you should have a guage figure corresponding to R134a @ 20 degrees - In my language 68 psi. or 4.6 bar. In excess of this could indicate the presence of non-condensibles, which leaves you no choice but to reclaim and re-charge. But if that side of things checks out OK, re-check your running figure which I would have thought should be around 110 - 120 psi, but i suspect you may find much higher. If so, I assume that the gas charge is correct, and that any TEV if fitted is working OK, then we come back to an undersized condenser and fan situation as has been mentioned already http://www.refrigeration-engineer.co...cons/icon9.gif .

Hope this helps

Trevor