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  1. #1
    On Approx. 30% of my calls, the H.O. has all or nearly all of the first floor registers closed in order to move more air to the second floor ; it doesnt work , and more importantly, it will almost always return liquid freon back to the Compressor in the A/C Unit ... which is designed to pump vapor only. Damage can and often results. The reason liquid gets returned is due to the air not flowing fast enough over the Cooling Coil to evaporate all the liquid freon when you have a bunch of registers closed . Nearly all duct systems in residences are undersized/poorly designed, and closing down registers only makes the system more choked down. Just want to give you a heads up as this is a very popular thing H.O.'s do without realizing the ramifications.

    Dave


  2. #2
    Join Date
    Dec 2002
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    in a house, Appomattox, Va.
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    3,255
    ANd I thought this thread was going to be about moving new construction registers for the new sofa- that'll be on the curb in 5 yrs.
    Col 3:23


    questions asked, answers received, ignorance abated

  3. #3
    Join Date
    Jun 2001
    Location
    Louisville, KY
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    12,155
    Then, it would be a good idea for contractors to install duct properly with balancing dampers.

  4. #4
    Join Date
    Apr 2005
    Location
    Chicagoland
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    209
    Originally posted by jrbenny
    Then, it would be a good idea for contractors to install duct properly with balancing dampers.
    Ditto

  5. #5
    Originally posted by jrbenny
    Then, it would be a good idea for contractors to install ductwork properly with balancing dampers.
    REPLY: I couldnt agree more. But, that is seldom the case even in custom built homes. Therefore, the H.O. needs to leave all the supply registers open and dont block returns with furniture, etc.

  6. #6
    Join Date
    Jul 2005
    Posts
    64
    Some of the ducts in my basement were blocked by the previous owner of the house...

    If the evap superheat is still good per manufacturer specs then there must still be enough airflow to allow evaporation, plus enough sensible heat loss to ensure there is no flooding to the compressor, right? (This would be accurate for the current load level at the time of testing, yeah? Would have to have the HVAC guy come back out check the superheat at low load also)

  7. #7
    Join Date
    Jul 2005
    Posts
    31
    I am just a homeowner who has also heard the tale concerning closing the registers to increase flow to the second story. I just want to make sure I understand the theory: By closing off the registers, it gives the air flowing through the 1st floor ducts no place to go, which increases the pressure. Zoning works differently by closing dampers at the beginning of the ducts, which allow the air to flow through the main trunk into the other open ducts, increasing flow to the open ducts (up to the limit of duct size). Am I getting it right?

    My 2 story house doesn't have automatic zoning, but it does have manual dampers on each duct coming off the main trunk. Would partially closing these dampers on the 1st floor work to increase flow to the second, or is that just as bad as closing the registers?


  8. #8
    Join Date
    Feb 2003
    Location
    Huntsville,AL
    Posts
    4,125
    one must keep a certain amount of air flow across the coils -- one may use dampers to change the air flow thru given ducts, so long as the minimum air flow is maintained across the inside coil --
    it does not matter which combination is chosen --

    dampers may be switched between summer & winter operation --
    with multiple stories, the dampers could be positioned in the trunks of each story, as opposed to necessitating attic access --

    still, it is best to maintain some air flow into each conditioned space to control humidity, at least part of the time ea da | night.

  9. #9
    Join Date
    Jun 2002
    Posts
    460
    Originally posted by hvacfella
    On Approx. 30% of my calls, the H.O. has all or nearly all of the first floor registers closed in order to move more air to the second floor ; it doesnt work , and more importantly, it will almost always return liquid freon back to the Compressor in the A/C Unit ... which is designed to pump vapor only.
    I'm curious, but doesn't a TXV help with this? (e.g. if the coil gets very cold, doesn't it meter less refrigerant into the coil?

    (No, I'm not advocating blocking registers, just wondering about those dehumidifying stages of the air handler operation which also reduce air flow over the coil)

  10. #10
    Join Date
    Aug 2002
    Location
    Office and warehouse in both Crystal River & New Port Richey ,FL
    Posts
    18,836
    We have found with proper Man D design,in our area,ducts in the attic ,curved blade adustable grilles,etc.,that grilles can be dampered ,at the grille and reduc air flow by 25% with no adverse effect.

    Now,that would part of the grilles,< 30% of them, not all of the grilles.

  11. #11
    Join Date
    Sep 2004
    Posts
    3,157
    ok so if blocking the regesters is a bad thing (and I understand why it is) what does a zoned system do differently. The zoned systems that we make will either close one side or the other or supply air to both outlets ( on a two outlet plenum)

    but by closing off one zone you are diverting all of the airflow to the other, and by closing all of the regesters on one floor you would force the airflow to the other.....ooooo smaller ducts going to the regesters increases static and reduces airflow through the system--- right?

  12. #12
    Join Date
    Jul 2005
    Posts
    947
    Dave the hvac-hobbyist makes blanket statements like this, please forgive him as he doesn't have a complete grasp of how stuff works yet.

  13. #13
    Join Date
    Jun 2002
    Posts
    460
    Originally posted by JoeSix
    I'm curious, but doesn't a TXV help with this? (e.g. if the coil gets very cold, doesn't it meter less refrigerant into the coil?
    I think I found my own answer...

    ...Now that more refrigerant is being introduced into the evaporator there is more availability to absorb heat, if there is insufficient heat to boil off all the refrigerant prior to it exiting the evaporator the temperature at the sensing bulb will decrease reducing the pressure at P1 and causing the valve to close...
    http://www.hvacmechanic.com/txv.htm

    Not that closing half the registers is a good idea, but I'd think a system with TXV might be less susceptible to floodback...


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