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Post by don on May 27, 2019 12:04:21 GMT
In about 2008 I had purchased a hydrocarbon blend refrigerant made by Envirosafe that was advertized as a drop in replacement for r12 and r134. I started making plans for converting a SO2 General Electric refrigerator to this refrigerant. I had read that hydrocarbon replacement refrigerants often will not work with high side floats so I needed to replace the float with a capillary tube.
When the neighbors moved out and their house was vacant I used the opportunity to drop the charge on the flattop refrigerator. It was a windy day and when I slowly released the gas thru tap a line valves that I had installed on both the low and the high side the smell was hardly discernable. I do not think the neighbors would have smelled anything. Here is my post on evacuating the 1938 Flattop and my conclusion that GENERAL ELECTRIC had added pentane to the system in the 1938 model year.
monitortop.freeforums.net/thread/1627/evacuating-so2-deja-vu?page=1&scrollTo=26667
After several deep evacuations the machine still had the residual SO2 smell that was working itself out of the oil. My plan was to charge the machine with the hydrocarbon refrigerant and after a trial run drop the charge and recharge in the hope that the SO2 would have worked itself out of the oil. I had removed the high side float and added a copper bullet refrigerant filter drier and 120 inches of .031 id capillary tube. I added a diaphragm refrigerant hand valve before and after the capillary tube fully anticipating the possibility of having to reduce the length of the tubing. Below is my post on the capillary hydrocarbon refrigeration experiment. I concluded from that experiment that the 120 inches of capillary obtained acceptable pressures for the HC blend and would be approximately close for any other r12/r134 drop in refrigerant. The hydrocarbon blend of propane and butane resulted in an unacceptible temperature glide that had formed ice on the entering side of the evaporator and was just very cold on the bottom and leaving side. Not good for an evaporator that had a temperature bulb attached to the bottom. My research also found that the hydrocarbon blends are not compatible with butyl hoses. My hoses must have had butyl in them as I had two high side hose gasket failures.
monitortop.freeforums.net/thread/1630/hydrocarbon-refrigerant-ge-flattop
Turbokinetic had suggested that he had used R152a as a replacement refrigerant and that it had worked even in systems that retained the original high side float. Since I had nothing to lose I decided to continue the experiment and bought the duster cans.
(Save the trigger spray heads and the extension wands as they fit perfectly on the top of my carburetor and throttle body cleaner cans and allows me to shoot cleaner fluid into passages and orfices)
I had taken the manual valves out of the system and after evacuating I added less than one can (8 ounces or so )into the machine and obtained an even frost pattern across the entire evaporator. The low side pressure was above 0# pressure - the amp draw was 2.4 amps and the high side condensing pressure was approx @ 30F above the 70F ambient . I fired up my original SO2 1940 flat top and compared frost lines. This AM I added more to try to match the frost line to ensure it is hi enuf so the engineered oil return feature functions.
The refrigerant r152a evidently works with a high side float or with a capillary tube. This means that sealed system repairs become more feasable. The use of a capillary tube with its considerable lower refrigerant charge and thus faster equalization of pressures could allow the use of a modern 1/8 HP compressor. The FEA machine I replaced the capillary tube on used 120 inches of .031 capillary with a charge of 9 ounces of r12 so the equalization times on this experiment should be the same and should be acceptible.
The oil return using R152a could be an issue? I found this in an online book which says that r152a is partly soluble in the mineral oil used in SO2 systems.
{A better HFC substitute for R12 is R152A. It too has very similar ther-modynamic characteristics to R12. The GWP is extremely low, and its lower molecular mass gives potential for energy saving. Ester oils may be used as the lubricant, although R152A is partially soluble in mineral oil and could be made fully soluble by the addition of a small proportion of isobutane (R600A). Two problems arise with this refrigerant: it has low thermal stability and it is slightly flammable. "Cold and Chilled Storage Technology by Clive Dellino"}
This experiment is in its third day and is still very preliminary and has not stood the +80 year test of time that SO2 has.
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Post by ckfan on May 27, 2019 14:27:53 GMT
Very neat stuff. I am enjoying reading about your experiments with this flat top. I hope the duster does well in it for you.
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Post by turbokinetic on May 27, 2019 21:20:34 GMT
Sounds like you've got a good runner there. Hopefully time will prove the cap tube length and charge amount are just right!
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Post by don on Jun 20, 2019 12:48:23 GMT
Now that the Flat Top refrigerator has ran long enuf to develop ice it is noticeable that some of the evaporator does not have an even coverage of ice.
The R-152a refrigerant leaving the capillary tube enters on the back of the evaporator on the left and crosses over to the right side on the first pass on the bottom of the evap. The right side of the evap has a series circuit culminating in a manifold that distributes the refrigerant to the rest of the evaporator thru six small passages that feed the parallel passes on the bottom and left side. The refrigerant flow is short circuiting thru the first three passages off the manifold at the end of the series circuit leaving no refrigerant flowing thru the next three passages. I did not notice this when it had SO2 running in it.
It could be that a capillary tube will not be a perfect substitute for the high side float. It might just need more refrigerant. When I find some extra time I will return to this project and refocus and try different approaches. The refrigerator as it is works well and cycles in this warmer weather we are having. I can live with this performance but this experiment might show the high side float is the best metering device.
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Post by turbokinetic on Jun 20, 2019 13:00:52 GMT
Now that the Flat Top refrigerator has ran long enuf to develop ice it is noticeable that some of the evaporator does not have an even coverage of ice.
The R-152a refrigerant leaving the capillary tube enters on the back of the evaporator on the left and crosses over to the right side on the first pass on the bottom of the evap. The right side of the evap has a series circuit culminating in a manifold that distributes the refrigerant to the rest of the evaporator thru six small passages that feed the parallel passes on the bottom and left side. The refrigerant flow is short circuiting thru the first three passages off the manifold at the end of the series circuit leaving no refrigerant flowing thru the next three passages. I did not notice this when it had SO2 running in it.
It could be that a capillary tube will not be a perfect substitute for the high side float. It might just need more refrigerant. When I find some extra time I will return to this project and refocus and try different approaches. The refrigerator as it is works well and cycles in this warmer weather we are having. I can live with this performance but this experiment might show the high side float is the best metering device.
Hey Don, glad to hear follow-up on this fridge! In the past, we've seen that sort of "bypassing" frost pattern when the evaporator is logged with oil. The oil would thicken up at the low temps, and provide a path of more resistance through the passages which are oil-logged. You might need to give it a heat-treatment to get things sorted out. Could be due to left-over oil from the HC refrigerant?
Have a great day!
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Post by don on Jul 2, 2019 21:48:57 GMT
Knowing full well the warnings about placing a refrigerator on its side I laid my 1938 Flattop on its left side and placed a 4 x 4 under the base so that any oil logged in the evaporator would drain out into the suction header. After 8 hours I rotated the prone refrigerator so that any oil in the suction header would then drain into the circuits closest to the front. If there had been oil logged in those circuits it would have drained into the circuits that had been working. After 8 hours I uprighted the refrigerator and after allowing time for the oil in the compressor to settle I turned on the compressor. After about a half hour run time it was obvious that the refrigerant was still short circuiting/bypassing. Since the series circuit on the right side of the evaporator had six feeds to the parallel circuits on the bottom and the refrigerant was only going thru the first feeds it was logical that maybe it needed more refrigerant. I had originally transferred two ten counce duster cans into my charging cylinder for a total of 20 ounces. The nametag of this machine showed it used 1 3/4# of SO2 for a total of 28 oz. I added the remainder of the 20 ounces from the cylinder and it was amazing to see the rest of the evaporator frost up. Eureka. After running it under a 85F environment it drew 2.4 amps and cycled. I shut it down and the next day when my garage ambient measured 95F I restarted the machine and measured the current. The current draw started at 2.8 amps and within a half hour the evap was fully frosted and the current draw was 2.4 amps. It cycled perfectly. This picture shows the frost level on the suction header leaving the evaporator with 20 ounces of r152a drive.google.com/drive/folders/1vRWltmLA-R6TlabykZy-XTRX0EEBTNEN This is the piping layout of the successful capillary conversion with R152a refrigerant drive.google.com/drive/folders/1vRWltmLA-R6TlabykZy-XTRX0EEBTNEN |
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Post by ckfan on Jul 3, 2019 0:24:01 GMT
That’s excellent. I’m glad to hear that adding more to it did the trick.
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Post by turbokinetic on Jul 3, 2019 11:58:07 GMT
Hi Don. Happy this is working for you! It does look like the frost line is good and the current draw is very reasonable.
Sincerely,
David
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Post by don on Jul 10, 2019 19:57:43 GMT
I have renamed the title of this thread to more accurately describe its contents. When I replaced the wiring on my 1940 Flattop I terminated the wire connections in a galvanized 4x4 electrical box attached close to the compressor with screws. The original start relay on this 1938 refrigerator with a capillary conversion using R152a refrigerant quit when I was test running the successful conversion. I temporarily replaced the wiring and relay leaving all the cables long so I could go back and clean them up later. Easy Access Wiring drive.google.com/drive/folders/1vRWltmLA-R6TlabykZy-XTRX0EEBTNEN Since the cables had extra length I decided to run them out to the front of the machine and terminate them there for an easier access for the future. I am going to leave it unanchored so it can be pulled out of the machine . I reused the original overload contacts and put them in series with the overoad contacts in the SUPCO SS relay. I let the SUPCO relay dangle out of the box so it could cool down faster. The 4x4 galvanized electric box I used on my 1940 Flattop was deeper and has more cubic inches than the plastic one used in this 1938 refrigerator. There is also the option of adding an extension to the metal box increasing the internal cubic inches even more. One cable on the top is coming from the original O.L. contacts - one cable is coming from the three motor winding leads - and one cable is coming from the cold control and light circuit in the machine top. The cable on the side is the power cord. If I replace the SS relay in the future with a mechanical current push on relay as coldspaces monitortop.freeforums.net/thread/37/ge-type-relay-modernizationdid in his post on this blog I will rigidly mount that relay in a vertical position in an additional anchored electric box with the motor leads going directly there . |
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