Zach
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Posts: 30
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Post by Zach on Jul 19, 2019 1:54:49 GMT
Well, with the arrival of the summer heat the fridge has developed a new issue. It will run for a few days in a row with no issue and then all of a sudden it will stop cooling and just run and run. The wattage the motor is drawing will "stick" somewhere in the middle of it's usual travel through a cycle and it will stay there until I shut it off. Once it has sat for an hour or so and it mostly defrosts it will run again just fine for a similar period of time.
My theory is that since it is now charged with r12, oil is migrating into the evaporator and greatly reducing cooling capacity until it reaches the point that it no longer will keep up with demand.
Of course once the evaporator warms up the oil is more easily displaced by the boiling refrigerant. It would seem my options are to charge it with something that doesn't carry mineral oil and is also capable of lifting the float, or modifying the evaporator and float assembly in some way.
To top things off I'm fairly certain the original shaft seal is leaking as well, although honestly we all knew that would happen.
Any input would be greatly appreciated. I've grown attached to this thing over the last few months but it is driving me crazy.
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Zach
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Post by Zach on Jul 20, 2019 4:17:41 GMT
I think I'm going to try a fresh charge of r134a and see what happens. I know it has a very similar liquid density to SO2 so it should have no problem lifting the float and floating the oil back up to the return line.
My only concern is of course the much higher pressures it likes to run at, but since It would appear no one else has tried it in a belt driven low side float machine I'll give it a try in the name of science.
If the new refrigerant will cure the oil return issue and give acceptable performance I'll pull the compressor and tear into it. Since the shaft seal held a charge of r12 for several months I am hopeful a good cleaning and a careful polish will be all it needs.
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Post by turbokinetic on Jul 20, 2019 12:54:58 GMT
I think I'm going to try a fresh charge of r134a and see what happens. I know it has a very similar liquid density to SO2 so it should have no problem lifting the float and floating the oil back up to the return line. My only concern is of course the much higher pressures it likes to run at, but since It would appear no one else has tried it in a belt driven low side float machine I'll give it a try in the name of science. If the new refrigerant will cure the oil return issue and give acceptable performance I'll pull the compressor and tear into it. Since the shaft seal held a charge of r12 for several months I am hopeful a good cleaning and a careful polish will be all it needs. Hi Zach; I'm happy you are continuing to work with the S-W fridge and that it has been running well (although leaking slowly). It seems these low side float systems really need a refrigerant which doesn't blend with oil, to get proper oil return. The R134A will probably be a good choice. The motor power should be enough to work once the system is cold already. When it's pulling down temp from a startup with warm cabinet, that will be the hardest time for it.
I've never tried to salvage a shaft seal. In my case I am able to turn down and polish the shafts with a lathe. By doing that I can adapt a modern dual-lip seal to the compressor and eliminate the tedious process of setting up a mechanical seal. Having said that, it interests me greatly to see how your mechanical seal restoration will go!
Sincerely, David
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Zach
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Post by Zach on Jul 21, 2019 15:53:23 GMT
It's been charged with r134a for two days now and so far it is running well. Charging it up was a little bit of a trick, I had to feed a little bit of it in, let it cool, then let some more in. Once it had enough in it to starting cooling the evap down it went a little faster. All in all it took over an hour to put just under 4lbs in it. It may be somewhat overcharged, but the receiver on this little unit is tremendous. It looks as though it could hold 5-6 lbs of refrigerant on its own, and besides, the float controls the level of refrigerant in the evaporator anyway so a little bit more reserve can't hurt.
Running pressure is around 7 psi on the low side and 130 on the high with the evap in the low ten's/high single digits. Much lower than I expected. Before it started to pull down and get cold the high side was closer to 175 which still isn't as bad as I was expecting. Likely due to the extra capacity in the receiver.
As far as performance goes the runtime seems to be about 50% longer than r12 which isn't unexpected, however the time spent cycled off is probably twice as long as it was before. I attribute that to the fact that the evap is now completely filled with refrigerant and refrigerant only, not half (or more) oil logged.
I suppose the next step is to see how long this charge stays in the system. I'm sure the smaller r134a molecules will find their way out much more quickly than r12 or even so2 did, unless the slightly higher pressures squeeze the sylphon a little harder.
We shall see...
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Post by turbokinetic on Jul 21, 2019 22:06:45 GMT
It's been charged with r134a for two days now and so far it is running well. Charging it up was a little bit of a trick, I had to feed a little bit of it in, let it cool, then let some more in. Once it had enough in it to starting cooling the evap down it went a little faster. All in all it took over an hour to put just under 4lbs in it. It may be somewhat overcharged, but the receiver on this little unit is tremendous. It looks as though it could hold 5-6 lbs of refrigerant on its own, and besides, the float controls the level of refrigerant in the evaporator anyway so a little bit more reserve can't hurt. Running pressure is around 7 psi on the low side and 130 on the high with the evap in the low ten's/high single digits. Much lower than I expected. Before it started to pull down and get cold the high side was closer to 175 which still isn't as bad as I was expecting. Likely due to the extra capacity in the receiver. As far as performance goes the runtime seems to be about 50% longer than r12 which isn't unexpected, however the time spent cycled off is probably twice as long as it was before. I attribute that to the fact that the evap is now completely filled with refrigerant and refrigerant only, not half (or more) oil logged. I suppose the next step is to see how long this charge stays in the system. I'm sure the smaller r134a molecules will find their way out much more quickly than r12 or even so2 did, unless the slightly higher pressures squeeze the sylphon a little harder. We shall see...
It seems that the seals get scratches and pitting from SO2 and moisture over the years. Some additional force holding the seal faces together could help; but more than likely a lapping would be required.
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Zach
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Posts: 30
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Post by Zach on Nov 25, 2019 14:59:45 GMT
Just thought I would give a 4 month update on the Stewart Warner.
I decided to take the “If it ain’t broke, don’t fix it” approach to this little fridge. I assumed the r134a would quickly leak out of the system since I had such poor results with r12, yet it continues to chug along just as it did back in July. A few months ago I borrowed a Bacharach detector and went over the whole system, amazingly it didn’t take any interest in the shaft seal area. Perhaps SW had a better designed shaft seal than Frigidaire and all of the others back then. Or maybe I’ve just gotten very lucky.. Either way, I’m going to let it continue to run. I don’t dare disturb the shaft seal now because it obviously doesn’t leak enough to cause an issue.
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Post by turbokinetic on Nov 25, 2019 15:05:31 GMT
Just thought I would give a 4 month update on the Stewart Warner. I decided to take the “If it ain’t broke, don’t fix it” approach to this little fridge. I assumed the r134a would quickly leak out of the system since I had such poor results with r12, yet it continues to chug along just as it did back in July. A few months ago I borrowed a Bacharach detector and went over the whole system, amazingly it didn’t take any interest in the shaft seal area. Perhaps SW had a better designed shaft seal than Frigidaire and all of the others back then. Or maybe I’ve just gotten very lucky.. Either way, I’m going to let it continue to run. I don’t dare disturb the shaft seal now because it obviously doesn’t leak enough to cause an issue. This is great, and confirms what we have heard for a while. The mechanical shaft seal faces do indeed "wear in" to each other and result in better sealing as they run. Definitely don't mess about with it. Paul's 1927 Frigidaire still has its original seal and holds just fine with R152A. Although it did not function correctly with R12 it, amazingly, held that charge while not being used, for years.
Thanks for the update!
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Post by gerald roman on Sept 26, 2021 15:09:50 GMT
As a kid watching the frig repairman working on a belt driven S/W ,I was told that the refrigerant was laughing gas ( nitrous oxide ) ?
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Post by turbokinetic on Sept 26, 2021 15:13:58 GMT
As a kid watching the frig repairman working on a belt driven S/W ,I was told that the refrigerant was laughing gas ( nitrous oxide ) ? That's funny! It was sulphur dioxide (SO2) which would be far from laughing gas! If nitrous oxide is laughing gas; then sulphur dioxide would be crying gas or sneezing gas or coughing gas! |
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