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  1. #1
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    Why a fridge can break during delivery: Design pressure and ambient temperatures.

    While looking at the parameters of domestic refrigerators, I realized one interesting fact.
    Domestic refrigerators (e.g. side-by-side ones) have the design pressure for the LS posted as 140 psi. See, e.g. this image: https://www.instagram.com/p/BWTOZ8WHSlN/ .
    Looking at R-134a on the pressure chart, I see that at 115 F, the pressure would be 147 psi, which technically exceeds the LS design pressure.
    As a reminder, the Glossary here defines the design pressure: "Highest or most severe pressure expected during operation". It would mean that if the refrigerator is transported in a truck when the ambient temperature is 115 F (It gets that high in TX, AZ, CA, ..., especially inside an enclosed truck.)
    I understand that those ratings have some "buffer zone". But, in principle, at those temperatures the system is not guaranteed to be alright.

  2. #2
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    I've redlined my car before, was ok.

    Sent from my SM-G920W8 using Tapatalk

  3. #3
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    I would expect that the "safety zone" should be about 30% from the nominal value. At the very least, that should provide the stability against production variations. But that's just a speculation.

  4. #4
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    So "during operation" , a 29 degree R134a fridge evaporator should see ~25 PSI. That gives you a 560% buffer from that design test pressure.

    I may be missing your point. Did you have a question?

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  5. #5
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    No, I didn't not have a question. This was just to share the thoughts.

    The point was that in a hot climate, the fridge might be exposed to the temperature (and hence, the pressure) outside of its "specification range".

    I am not sure if all people (or anybody at all) transporting fridges (long-haul 18-wheelers and local delivery trucks -- from Home Depot, Lowe's, Best Buy, etc.) are aware of that.

    PS. I might be missing something in this consideration. Am I?

  6. #6
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    Quote Originally Posted by StR View Post
    While looking at the parameters of domestic refrigerators, I realized one interesting fact.
    Domestic refrigerators (e.g. side-by-side ones) have the design pressure for the LS posted as 140 psi. See, e.g. this image: https://www.instagram.com/p/BWTOZ8WHSlN/ .
    Looking at R-134a on the pressure chart, I see that at 115 F, the pressure would be 147 psi, which technically exceeds the LS design pressure.
    As a reminder, the Glossary here defines the design pressure: "Highest or most severe pressure expected during operation". It would mean that if the refrigerator is transported in a truck when the ambient temperature is 115 F (It gets that high in TX, AZ, CA, ..., especially inside an enclosed truck.)
    I understand that those ratings have some "buffer zone". But, in principle, at those temperatures the system is not guaranteed to be alright.

    When not operating, pressures can be higher. They are not operating inside of a truck.
    Experience - knowing when to get the hell out of the way and plug your ears. "Don't be a sissy. Turn it on!"
    Poodle Head Mikey - "the world is well populated with the unknowing and the uncaring and the stupid."

  7. #7
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    Shouldn't that read "Test Pressures"?

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  9. #8
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    Quote Originally Posted by pecmsg View Post
    Shouldn't that read "Test Pressures"?
    In the glossary or on the tag?

    Quote Originally Posted by HVAC_Marc View Post
    When not operating, pressures can be higher. They are not operating inside of a truck.
    So, the question is what is the limiting factor (the bottle neck) for that design pressure: the pressure that the elements can sustain or the pressure that the compressor can operate with.
    My consideration above was based on the former. If it is the latter, then indeed, it is important only while the fridge is operating.

    Indeed, some home appliances have two temperature ranges (and sometimes humidity) specified in the manuals: "operating" and "storage". I don't remember if the manual for refrigerators are like that.

  10. #9
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    Quote Originally Posted by Bunyan View Post
    So "during operation" , a 29 degree R134a fridge evaporator should see ~25 PSI. That gives you a 560% buffer from that design test pressure.
    Sorry, I missed this point earlier.
    I think your conclusion is not completely correct. When you turn on a refrigerator and it starts operating, the ambient temperature determines the pressure, which you can see on that chart. And that pressure is much higher, 60-80 PSI, depending on the ambient temperature. When the evaporator cools down, then yes, - your numbers become relevant.

  11. #10
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    with a fixed metering device AKA Cap Tube the pressure will have a minimum no mater how warm it is.

  12. #11
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    Quote Originally Posted by StR View Post
    So, the question is what is the limiting factor (the bottle neck) for that design pressure: the pressure that the elements can sustain or the pressure that the compressor can operate with.
    It's the functionality of the cooling process. The equipment can handle much larger pressures.
    Experience - knowing when to get the hell out of the way and plug your ears. "Don't be a sissy. Turn it on!"
    Poodle Head Mikey - "the world is well populated with the unknowing and the uncaring and the stupid."

  13. #12
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    I guess I only work on commercial and industrial refrigeration, but regardless of compressor, suction pressure plummets quickly and dramatically on any compressor startup. So the vast majority of the systems operating pressure, will actually be way under the "highest or most severe pressures expected during operation". I don't know if we'll be able to give you a satisfactory answer outside of referring you to the engineering department of the manufacturer.

    Food for thought, at a factory training session for an ice machine manufacturer last year they revealed they were using a different refrigerant for some of their newer model offerings yet still using the same evaporators across the board. When I asked how that was possible (R410a runs about 30% higher pressures than R404a at the same temps) I was told the evaporators and materials were tested to be well within design specs and could really even handle much higher. No hard numbers, but still illustrates the gist. Again, you may need a materials engineer to tell you the specific break point and the stresses they can endure.

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