Repurposing R600A compressor in 1960's Coldspot freezer...
Jan 5, 2023 15:43:14 GMT
cablehack, ckfan, and 1 more like this
Post by turbokinetic on Jan 5, 2023 15:43:14 GMT
This one was fun and it will be interesting to see how the longterm results are. The first part of the video is troubleshooting the original compressor, and musing about the previous repairs found. After that, an experimental modification is made!
A bit of a backstory is in order. This is very basic and all the experienced repair guys may find it boring. But here goes. It's important to understand why this is significant and worth understanding my reasoning.
Many of us prefer to salvage and repurpose things in the interest of keeping our vintage appliances going. Often, this is the only way. There was a time when it was pretty easy to locate like-for-like compressors for older fridges and freezers. Unfortunately now, this isn't as simple as it used to be.
Older fridges and freezers typically had R12 as the refrigerant, and the compressor was lubricated with mineral oil. R12 has moderate discharge temperatures which don't harm the mineral oil. Because R12 has been made obsolete, there is a need for alternatives. The first replacement for R12 was R134A, which works OK in systems designed for it, but produces very high discharge temperatures. It requires synthetic oils to prevent oil carbonization and fouled valves in the compressor due to these temperatures. The synthetic oils for R134A are sensitive to system contamination and have a nasty habit of forming solid particles which clog the system.
Clogging is particularly a problem on "converted from R12" systems where the capillary tube is inaccessible and it's not possible to remove all traces of the old oil from the system when switching from mineral to synthetic oils. For this reason, it's more tedious and time-consuming to repurpose a salvaged R134A compressor to work reliably in an older mineral oil system.
Now, R134A is falling out of favor and being replaced with R600A in home fridges. The compressors designed for R600A come with mineral oil because that refrigerant does not produce high discharge temperatures.
Now, it's possible to get R600A salvaged compressors very reasonably, in small sizes suitable for our old fridges. They won't have the oil solidification problems of R134A systems. The problem with them is the operating pressure, and flammability hazard of R600A. The compressor is not designed to operate at the pressures of R12 or R12 replacements because R600A operates at lower pressures. R600A is unsuitable for older designs because of the amount of gas required poses a significant flammability hazard compared to systems engineered for R600A.
For that reason, another alternative is needed. The alternative I have been testing is R1234ZE. This is one of the latest HFO (hydrofluoro-olefin) refrigerants. It is quite expensive and therefore only feasible for small systems at this time. R1234ZE has replaced R114 in the older Frigidaire units from the early 30's, successfully. My earlier tests of this are still working after multiple years, as are some other peoples' tests with it.
With any capillary tube system, the amount of flow through the cap tube is a very important parameter. It has to match the compressor capacity and properties of the refrigerant in use. There is info out there to allow changing from R12 to R134A or R152A by adding length to the capillary tube. For R1234ZE there is virtually no information available. It has been proven that the original R114 cap tube on the early Frigidaires works as-is with R1234ZE.
The Coldspot freezer in this video was an R12 system with a 1/6 HP compressor. The new compressor is also rated at 1/6 HP (note that it is Chinese so the rating may or may not compare to the origiginal Tecumseh).
The experiment is to replace the compressor and charge with R1234ZE, and see what sort of system performance we get with no other changes. I was not expecting the cap tube to be appropriate in flow, considering the change in pressures and refrigerant liquid density. However, it really surprised me.
Disclaimer: As with all facets of engineering there are no "hard and fast, absolute" rules. There are many different system designs out there. For that reason, it's very important to do proper due diligence and testing. This may not work for you, or it may require more modifications for other systems, than this one required. There is no such thing as a "drop in replacement refrigerant" for "any system originally using any specific refrigerant." All refrigerants have different properties, and it is very important to know that changing gases will change the performance of the system; regardless of whether or not that gas is "listed to replace" any given refrigerant. Our goals are to chose alternatives which result in minimal negative impacts on the system.
Hope y'all have enjoyed this and found it informative!
Sincerely,
David
https://youtu.be/Rteww-ovkYU
A bit of a backstory is in order. This is very basic and all the experienced repair guys may find it boring. But here goes. It's important to understand why this is significant and worth understanding my reasoning.
Many of us prefer to salvage and repurpose things in the interest of keeping our vintage appliances going. Often, this is the only way. There was a time when it was pretty easy to locate like-for-like compressors for older fridges and freezers. Unfortunately now, this isn't as simple as it used to be.
Older fridges and freezers typically had R12 as the refrigerant, and the compressor was lubricated with mineral oil. R12 has moderate discharge temperatures which don't harm the mineral oil. Because R12 has been made obsolete, there is a need for alternatives. The first replacement for R12 was R134A, which works OK in systems designed for it, but produces very high discharge temperatures. It requires synthetic oils to prevent oil carbonization and fouled valves in the compressor due to these temperatures. The synthetic oils for R134A are sensitive to system contamination and have a nasty habit of forming solid particles which clog the system.
Clogging is particularly a problem on "converted from R12" systems where the capillary tube is inaccessible and it's not possible to remove all traces of the old oil from the system when switching from mineral to synthetic oils. For this reason, it's more tedious and time-consuming to repurpose a salvaged R134A compressor to work reliably in an older mineral oil system.
Now, R134A is falling out of favor and being replaced with R600A in home fridges. The compressors designed for R600A come with mineral oil because that refrigerant does not produce high discharge temperatures.
Now, it's possible to get R600A salvaged compressors very reasonably, in small sizes suitable for our old fridges. They won't have the oil solidification problems of R134A systems. The problem with them is the operating pressure, and flammability hazard of R600A. The compressor is not designed to operate at the pressures of R12 or R12 replacements because R600A operates at lower pressures. R600A is unsuitable for older designs because of the amount of gas required poses a significant flammability hazard compared to systems engineered for R600A.
For that reason, another alternative is needed. The alternative I have been testing is R1234ZE. This is one of the latest HFO (hydrofluoro-olefin) refrigerants. It is quite expensive and therefore only feasible for small systems at this time. R1234ZE has replaced R114 in the older Frigidaire units from the early 30's, successfully. My earlier tests of this are still working after multiple years, as are some other peoples' tests with it.
With any capillary tube system, the amount of flow through the cap tube is a very important parameter. It has to match the compressor capacity and properties of the refrigerant in use. There is info out there to allow changing from R12 to R134A or R152A by adding length to the capillary tube. For R1234ZE there is virtually no information available. It has been proven that the original R114 cap tube on the early Frigidaires works as-is with R1234ZE.
The Coldspot freezer in this video was an R12 system with a 1/6 HP compressor. The new compressor is also rated at 1/6 HP (note that it is Chinese so the rating may or may not compare to the origiginal Tecumseh).
The experiment is to replace the compressor and charge with R1234ZE, and see what sort of system performance we get with no other changes. I was not expecting the cap tube to be appropriate in flow, considering the change in pressures and refrigerant liquid density. However, it really surprised me.
Disclaimer: As with all facets of engineering there are no "hard and fast, absolute" rules. There are many different system designs out there. For that reason, it's very important to do proper due diligence and testing. This may not work for you, or it may require more modifications for other systems, than this one required. There is no such thing as a "drop in replacement refrigerant" for "any system originally using any specific refrigerant." All refrigerants have different properties, and it is very important to know that changing gases will change the performance of the system; regardless of whether or not that gas is "listed to replace" any given refrigerant. Our goals are to chose alternatives which result in minimal negative impacts on the system.
Hope y'all have enjoyed this and found it informative!
Sincerely,
David
