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  1. #1
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    Piping size differences between evap and CU

    I have an install coming up where I’m not supplying the equipment. The dealer gave me the specs and the CU line set connections are 1/2” & 7/8”. The evap is 3/8” & 5/8”. I usually go with the larger line size in these situations but what’s the rule?

  2. #2
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    You go by the chart that is inside of the install manual. It may or may not be the same size as the stubs that come out of either of your coils.

    The downside of too small is less capacity, while the downside of too large is poorer oil return. Pick your poison.
    If at First You Don't Succeed, Skydiving Is Not for You.

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  4. #3
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    Don’t go by indoor or outdoor unit pipe connections. Size the pipe properly.

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  6. #4
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    Quote Originally Posted by VanMan812 View Post
    I have an install coming up where I’m not supplying the equipment. The dealer gave me the specs and the CU line set connections are 1/2” & 7/8”. The evap is 3/8” & 5/8”. I usually go with the larger line size in these situations but what’s the rule?
    The 1/2 can act as a male coupling to the 3/8 and the 7/8 can act as a male coupling to the 5/8. You might have to swage it in a little. Either with a swaging tool or the tip of your needle nose. Although be sure you don't get copper dust inside the line or else/and make sure you flush it well with nitro before assembly.

    Sent from my LG-TP450 using Tapatalk

  7. #5
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    Quote Originally Posted by VanMan812 View Post
    I have an install coming up where I’m not supplying the equipment. The dealer gave me the specs and the CU line set connections are 1/2” & 7/8”. The evap is 3/8” & 5/8”. I usually go with the larger line size in these situations but what’s the rule?
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  9. #6
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    Quote Originally Posted by VanMan812 View Post
    I have an install coming up where I’m not supplying the equipment. The dealer gave me the specs and the CU line set connections are 1/2” & 7/8”. The evap is 3/8” & 5/8”. I usually go with the larger line size in these situations but what’s the rule?
    What's the rule?

    When it comes to system line size, the Rule #1 is: Never, ever use equipment connection sizes to size piping.

    Use the installation manual piping guidelines provided by the manufacturer or use a good pipe sizing chart or program. Here's a good online sizing program from Tecumseh which includes sizing for suction, discharge and liquid lines for most common refrigerants. It also selects for the required suction riser size, condenser drain line size and calculates for both the refrigerant velocity and pressure drop.

    http://boxload.tecumseh.com/RefLineSizing.aspx

    Also...Whenever installing equipment provided by others, whether new or used, it's advisable that you, as the installing contractor, first do a check to verify that the system components selection is a good match. If possible, do a load calculation as well. You may be saving yourself and your customer an unnecessary and costly surprise. Check if all required loose components are provided like TXV, liquid line solenoid, thermostat, filter-drier, sightglass, defrost timer, etc.

    Remember, there's usually only one (hopefully knowledgeable) person who has made the selection, like the supply house sales engineer, and you may be the only other person capable of reviewing it before installation.

  10. #7
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    Quote Originally Posted by icemeister View Post
    What's the rule?

    When it comes to system line size, the Rule #1 is: Never, ever use equipment connection sizes to size piping.

    Use the installation manual piping guidelines provided by the manufacturer or use a good pipe sizing chart or program. Here's a good online sizing program from Tecumseh which includes sizing for suction, discharge and liquid lines for most common refrigerants. It also selects for the required suction riser size, condenser drain line size and calculates for both the refrigerant velocity and pressure drop.

    http://boxload.tecumseh.com/RefLineSizing.aspx

    Also...Whenever installing equipment provided by others, whether new or used, it's advisable that you, as the installing contractor, first do a check to verify that the system components selection is a good match. If possible, do a load calculation as well. You may be saving yourself and your customer an unnecessary and costly surprise. Check if all required loose components are provided like TXV, liquid line solenoid, thermostat, filter-drier, sightglass, defrost timer, etc.

    Remember, there's usually only one (hopefully knowledgeable) person who has made the selection, like the supply house sales engineer, and you may be the only other person capable of reviewing it before installation.
    Too add to this......

    The sales company really doesn't care what happens just as long as the box reaches temperature. Do they care if the equipment is so oversized that theirs no humidity control, equipment short cycles, not enough run time for proper oil return?

  11. #8
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    Quote Originally Posted by pecmsg View Post
    Too add to this......

    The sales company really doesn't care what happens just as long as the box reaches temperature. Do they care if the equipment is so oversized that theirs no humidity control, equipment short cycles, not enough run time for proper oil return?
    True, but I found more often than not, equipment dealers select the equipment using the lightest load conditions on the manufacturer's sizing chart...ie, the equipment size is minimized to achieve the lowest possible price. If it doesn't make temperature, they simply blame the chart.

  12. #9
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    The last 2 gas station beer caves were way oversized. One so bad during mild weather the box's get damp.

    This next one i think i have them convinced to get 2 systems, each 60 - 70% of full load. They aren't happy when they only have 1 system and something fails and there down for a few days!

  13. #10
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    Thread Starter
    Yep, that’s the right answer.... size it myself. I knew that🤦*♂️

    Thank you!


    Sent from my iPhone using Tapatalk

  14. #11
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    Quote Originally Posted by ammoniadog View Post
    You go by the chart that is inside of the install manual. It may or may not be the same size as the stubs that come out of either of your coils.

    The downside of too small is less capacity, while the downside of too large is poorer oil return. Pick your poison.
    I have also found that to small suction on a long run increases head pressure. I have run a larger line and dropped the size down about 3 feet from compressow to increase velocity.

  15. #12
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    Quote Originally Posted by lytning View Post
    I have also found that to small suction on a long run increases head pressure. I have run a larger line and dropped the size down about 3 feet from compressow to increase velocity.
    Are you sure? I would think it would be the other way around. I'm pretty sure too small of a suction line would act like a restriction, which would lower the suction pressure, which in turn would lower the head pressure.

    Also, your last sentence seems backwords too. You said you run bigger pipe to increase velocity? Im pretty sure the bigger the pipe is, the slower the refrigerant inside of it will be moving.
    If at First You Don't Succeed, Skydiving Is Not for You.

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  17. #13
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    Quote Originally Posted by lytning View Post
    I have also found that to small suction on a long run increases head pressure. I have run a larger line and dropped the size down about 3 feet from compressow to increase velocity.
    Maybe you mean higher discharge temp, not pressure.

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