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Is the U-bend (in 1st picture) necessary? I'm guessing it's preventing backflow of gas from the drain.

My A/C (heatpump) is leaking condensation.

BACKGROUND

TESTING:

  1. Disconnected the drain pipe below the "u" and drained into a bucket. NO LEAKING in drain pan for the 36 hours of testing. Bone dry.
  2. Reconnected. Moved the terminating end from the floor drain to a small pan. It filled 1 pint in about an hour.
  3. With everything hooked up properly, it's probably a pint in 8 hours. When I originally discovered it (b/c it was overflowing to the floor) it was full. So probably 3 gallons or so.

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Drip Pan This is where water is collecting. (Yes, that's newspaper in there, attempting to get it dry before one of the tests) enter image description here enter image description here

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Is the U-bend (in 1st picture) necessary? I'm guessing it's preventing backflow of gas from the drain.

It is required by code to do just what you said. It prevents sewer gas from venting into the A/C and then into the house. You would not want that.

Make sure it is not clogged, but do not remove it.

  • The U bend collects water and restricts the wasteful flow of air out the condensate drain line. My system does not have that and it flows freely, but it has an air gap where the condensate line goes into the sanitary sewer. So I am probably having more loss of air out the condensate line. This lost air is not chilled air but it is air pumped out of the conditioned space which will be replaced by infiltration from outside (which is not desirable). The sanitary sewer opening in my system must have a trap under the slab because I get no smells. I don't know about your system. – Jim Stewart Jul 27 '17 at 15:44
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    You need to gain access to the A/C coil area and check the drip pan which is below the bottom of the coil. The pan may be rusted out or corroded through the metal and leaking down the heating unit. The pan may also be loaded with dirt and debris preventing the water to drain properly. If the coil itself is dirty the condensate could drip off the coil and down to where you placed the paper. – d.george Jul 27 '17 at 16:01

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