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liquid line size

I did a heat load calculation for a house via software and came up with 2 tons. the home owner (my niece's husband) likes it to be as cold as possible. so I decided on a 2 1/2 ton. they just bought the house and the old unit was a 3 ton r-22 system. to make a long story short I replace the whole system (air handler and condensing unit with a R410 system. on the hottest day we've had this year (upper 80s) the inside temp. got to 71 degrees according to the thermostat. he has it set for 68. I don't mind trying to get it colder which leads me to my question.
the old 3 ton unit had a 3/4 suction line (not 7/8) and the liquid line was only 5/16 (not 3/8). the new 410 system was factory fitted for a 3/8 liquid line. I didn't change the line set.
will changing the liquid line from 5/16 to 3/8 enable the system to make the house a couple of degrees cooler.


    HVACNUT Member Posts: 3,790
    You should have installed a new line set, according to manufacture specs, especially when changing refrigerants.
  • ChrisJ
    ChrisJ Member Posts: 11,491
    edited July 2017
    How long is the linset? How much if any lift on the liquid line?

    From what I'm seeing, no, changing to 3/8 won't provide any benefit in most situations on 2.5 ton.

    Insulating the liquid line if it's in an attic may help greatly though.
    Single pipe quasi-vapor system. Typical operating pressure 0.14 - 0.43 oz. EcoSteam ES-20 Advanced Control for Residential Steam boilers. Rectorseal Steamaster water treatment
    EBEBRATT-Ed Member Posts: 8,467
    I use the DuPont Refrigeration Handbook for sizing. @2 1/2 ton R410A 3/4 OD suction is good for up to 100'

    5/16 liquid isn't even listed even a 1.5 ton unit they call for a 3/8 liquid.

    3/8 liquid is good for 50'run at 2 1/2 tons. over that I would go to 1/2"

    You need to take superheat and subcooling measurements to see what's going on. 5/16 may be ok on a short run.

    Just because they want it as cold as possible ......well I won't say what I think. No need to be below 74 deg unless you have serious humidity issues.

    according to your calculations the unit is 1/2 ton oversized. Find out whay it's not doing the job

    pressures & airflow
    TD across ahu should be 20 deg

    Is the ductwork tight?? Insulated? sealed?

    to many questions, need more info
    HVACNUT Member Posts: 3,790
    You used the existing line set, but did you run cleaner through it, then nitro? Your refrigerant might be contaminated from the R22 oil.
  • ChrisJ
    ChrisJ Member Posts: 11,491
    My understanding is 410A simply won't bring back mineral oil. I recall people saying you couldn't mix POE and mineral, but I believe that's been proven wrong and is considered harmless in small percentages? Don't quote me on that though.

    Either way, I agree, I hope the lineset was blown out with N2 and flushed.

    I doubt that has to do with the OP's issue though.

    More importantly, what temperature difference are you seeing across the coil on hot days? I.E., what's the temperature drop from the return temp, to the supply temp?
    Single pipe quasi-vapor system. Typical operating pressure 0.14 - 0.43 oz. EcoSteam ES-20 Advanced Control for Residential Steam boilers. Rectorseal Steamaster water treatment
  • newagedawn
    newagedawn Member Posts: 587
    bigger is not better in cooling or heating, trust the heat loss calc if its correct and ALL the numbers are right. i agree with other comments about the line set , that it should be changed with the new system of 410a, ive done it alot this summer and have had no problems, its more work but worth the end result
    plus, when its 80 degrees in the house it will take a day to get all the humidity out of the house, air conditioning doesnt work like Mcdonalds it doesnt happen in a micro second,
    also check the delta t of the coil if its 20 degrees its working just have to be patient and let it take the humidity out
    "The bitter taste of a poor install lasts far longer than the JOY of the lowest price"
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