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Thread: Adapter Stub Length Question

  1. #1
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    Question Adapter Stub Length Question

    New complete three ton A/C only unit and line-set. The condenser and evaporator are both 3/4" at the outlets. Goodman is calling for the 27' line-set to be 7/8".

    My question is... are there any issues running 3/4" line, for two feet, (from evap and condenser) then using an adapter to connect to the 23' 7/8" line? I would like to do this at each end. This will reduce the number of brazed joints. Ideally, I know, would be to use a short 3/4" line copper stub to on each end for the transitions.

    My concern is oil flow return to the scroll compressor.

    Below is a model of what I would like to install.

    Evaporator > 3/4" line for 2' > 3/4" to 7/8" adapter > 7/8" line for 23' > 7/8" to 3/4" adapter > 3/4" line for 2' > Condenser

    Thank you for your comments! Doc Doug

  2. #2
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    Are you licensed and qualified to install HVAC systems? If so, I don’t understand how running 7/8 for the full length is a problem.
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  3. #3
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    If the Air Handler is higher than the outdoor unit Goodman ( install guide ) wants the vapor line to be a inverted loop near the AH, so thinking your lineset may be a tad longer, unless you took that into consideration, again if Air Handler is higher than the outdoor unit.

    Wouldn’t the Installing Contractor know all this, if your using a licensed insured Company.

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  5. #4
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    Quote Originally Posted by Bazooka Joe View Post
    If the Air Handler is higher than the outdoor unit Goodman ( install guide ) wants the vapor line to be a inverted loop near the AH, so thinking your lineset may be a tad longer, unless you took that into consideration, again if Air Handler is higher than the outdoor unit.

    Wouldn’t the Installing Contractor know all this, if your using a licensed insured Company.
    Might want to add Qualified!

  6. #5
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    Quote Originally Posted by Doc Doug View Post
    New complete three ton A/C only unit and line-set. Goodman is calling for the 27' line-set to be 7/8".

    My concern is oil flow return to the scroll compressor.
    Thank you for your comments! Doc Doug
    3-ton system is calling for 7/8” for 27’? Naw, I don’t think you’re reading the install manual correctly.
    Oil return concerns? 7/8” suction I would surely be concerned.


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  7. #6
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    Quote Originally Posted by pecmsg View Post
    Might want to add Qualified!
    Yes!, your correct,.. taking a line from the music artist Meat Loaf song,...Two Out Of Three Ain’t Bad...

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  9. #7
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    Thread Starter
    Most of us smaller guys stick to swap outs. In this case, it is a new install. Yes, I did the manual J but used the existing duct work for the gas furnace. The duct work can handle the 1200 CFM with no problem for cooling. For a 3 Ton R410A installation, the Goodman installation manual calls for 3/4" return, up to 0 - 24' return line. A 25' - 49' line calls for 7/8" return line.

    I agree, it seems large to me too... but this is what the "qualified" engineers at good old Goodman (Daikin) have in their manual. No need for an inverted vapor line... the air handler is only 3-4 feet lower than the condenser.

    I generally like to keep the line size (7/8" in this case) for the entire length on new installs... but also like to reduce the number of joints. (I have seen some real butchered splice jobs over the years.) In this case, since the equipment is only 3/4" at each end and it was nearly impossible to run the new line-set right up to the outlets, I figured that I would come out of the end fittings with 3/4" for 2 feet and use an adapter to 7/8". I guess I answered my own question.

    I was looking for feedback on reliability of oil return (sound of unit and life) from those that have experience using 7/8" line-set for a 3 ton Goodman, just over the 25' run. I am no expert in reading the charts but it appears the oil circulation is around 1,100 at FPM in the case?

    Thank you! - Doug

  10. #8
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    Is the condenser above the evap. If not, the larger vapor line has no virtually no effect on oil return. It simply gets you about 500 BTUs an hour more cooling than a 3/4" vapor line.
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  12. #9
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    Quote Originally Posted by beenthere View Post
    Is the condenser above the evap. If not, the larger vapor line has no virtually no effect on oil return. It simply gets you about 500 BTUs an hour more cooling than a 3/4" vapor line.
    The inlet of the condenser is approximately 24 inches higher than the evaporator outlet. I still have the option of coming off the evaporator with 3/4" for the two feet upward then transitioning to 7/8" line for the trip to the condenser... with a 2-3 three inch fall over the 25 feet back to the condenser. The upward 24 inches of 3/4" from the evaporator, should ensure a nice 1300 - 1400 fpm flow... until it meets the 7/8" where it will slow to 1000 1100 fpm. This should ensure the oil is blasted up and flowing straight for the condenser with a slight down slope for oil drip when off?

    Dunno. Sounds good in theory. I am assembling the line-set this week.

    On a side note, I typically remove the schrader valve on Goodman coils, inside the case on the factory 1/4" flare connection, before I attach the TXV flare nut. I understand this may not be necessary, since the Goodman TXV flare nut has a depressor that opens the schrader valve. This is apparently where Goodman charges the coil with Nitrogen for pressure testing. (Hence the schrader valve?) What do others do with the schrader valve, on the coil, before installing the TXV flare nut?

    Thanks!

  13. #10
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    Then neither line size will have any real effect on oil return.

    The 7/8" line size is just to get closer to the SEER/EER rating, and won't have any noticeable effect on cooling performance. Its only about a 5 BTU loss per foot of line difference between 7/8 and 3/4".
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