A/C Condensaye drain P-Trap venting problem

Discussion in 'HVAC Heating & Cooling' started by bmusgrove, Jun 13, 2014.

  1. bmusgrove

    bmusgrove New Member

    Jun 13, 2014
    Cedar Hill, Texas
    Discovered this weekend My primary condensate drain was not working after noticing water in the emergency / auxiliary drain pan. The line did not have a clean out before the P trap (see attached picture), nor did I have secondary drain line . I decided to remedy that problem since I would have to cut the PVC to clean it out. Cut the line cleaned the gunk blocking the condensate pan primary drain outlet (P-Trap was clean). I added a clean out before the P-trap and capped it and secondary uncapped drain line with no P trap.. Now I have a capped clean out before the P trap. Test fitted the pieces, Verfied the drain sloped away from the unit,and fired up the AC to test it. Did not work. A little experimenting revealed that if I cap the upstream clean out it will not drain. If I uncap it it drains beautifully.

    My mind is baffled. It makes no sense. This is positive pressure coil, on a Trane XV80 gas furnace (not a condensing heater). I put a small inspection camera in the unit. When I cap the vent, the water just goes in a circle in front of the drain, like a whirlpool. I have let the water level get roughly as high as the bottom of the secondary drain to no avail.




  2. Lone Star Charles

    Lone Star Charles New Member

    Jan 17, 2013
    I suspect there may be a clog further on down the line. I have seen where the AC installer tapped the nearest plumbing vent line for the condensate drain. After a few years of AC condensate and Texas sunshine coming down the same plumbing vent, the slimy mold growth inside the vent would clog the vent completely - backing up into the condensate line. Easy enough to clean out with a little bleach down the line or perhaps something a little stronger followed with a good flushing with water.
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