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  1. #1
    Join Date
    Feb 2001
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    447

    Question condensate traps

    Besides blocking air leaks and insects, what are the reasons for a condensate trap? Why would you want a trap before a condensate pump?

  2. #2
    Join Date
    Nov 2008
    Location
    Bristol Va.
    Posts
    633
    to allow a negative pressure drain to drain.

  3. #3
    Join Date
    Sep 2003
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    1,677
    Preventing sewer gas migration into the plenum

  4. #4
    Join Date
    Oct 2010
    Location
    Anderson, South Carolina, United States
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    7,778
    Quote Originally Posted by DOGBOY View Post
    to allow a negative pressure drain to drain.
    X2

  5. #5
    Join Date
    Aug 2012
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    2,755
    To grow microbes and clog so we can charge you to clear every six months.
    My name is TooCoolforschool and I am a chronic over charger.

  6. #6
    Join Date
    Feb 2001
    Posts
    447

    Question

    Quote Originally Posted by DOGBOY View Post
    to allow a negative pressure drain to drain.
    Are y'all saying that without a trap, in a residential size system, a drain on the negative pressure side of an evaporator coil would not be able to drain any condensate? That the air rushing back through the condensate drain would pull all the condensate toward the coil? If so, why wouldn't the negative pressure pull a trap dry too? The trap itself has to fill with condensate before it becomes functional.

  7. #7
    Join Date
    Oct 2010
    Location
    Anderson, South Carolina, United States
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    7,778
    Quote Originally Posted by charles2 View Post
    Are y'all saying that without a trap, in a residential size system, a drain on the negative pressure side of an evaporator coil would not be able to drain any condensate? That the air rushing back through the condensate drain would pull all the condensate toward the coil? If so, why wouldn't the negative pressure pull a trap dry too? The trap itself has to fill with condensate before it becomes functional.
    Yes, it would only drain when the blower shut off. the trap should be primed on start up (hold your hand over the outlet of the pipe til the trap fills). the trap has to be deeper than the external static pressure of the system so that it doesn't pull the water out of the trap.

  8. #8
    Join Date
    Nov 2008
    Location
    Bristol Va.
    Posts
    633
    Quote Originally Posted by charles2 View Post
    The trap itself has to fill with condensate before it becomes functional.
    An air conditioner usually is turned on in the spring when it starts to get warm so the run times are shorter and there is not as much humidity in the air so that there is ample time for the trap to fill up on its own when the blower shuts off. However if you where to turn it on for the first time when the house or space was 5 warmer than you like it and the outside temp was say 85 or higher you would have such a long run time that the water would not drain and you would have a water leak. That is until the blower were to turn off and allow the trap to fill up.

  9. #9
    Join Date
    Jul 2009
    Location
    South Carolina
    Posts
    3,366
    Quote Originally Posted by charles2 View Post
    Are y'all saying that without a trap, in a residential size system, a drain on the negative pressure side of an evaporator coil would not be able to drain any condensate? That the air rushing back through the condensate drain would pull all the condensate toward the coil? If so, why wouldn't the negative pressure pull a trap dry too? The trap itself has to fill with condensate before it becomes functional.
    It's not that it won't be able to drain any condensate, but that the negative pressure causing air to suck into the drain obstructs the flow of the condensate and holds the water back. To what degree you don't know but it can be substantial enough to cause problems. The trap keeps the air out so unless the negative pressure is strong enough to suck the weight of the water in the trap, the condensate will drain according to gravity without any interference. I've seen trapless units drain O.K. and I've seen some that would not drain at all. There can also be other contributing factors in the drain line that can make things more complicated.
    Gary
    -----------
    http://www.oceanhvac.com
    An engineer designs what he would never work on.
    A technician works on what he would never design.

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