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View Full Version : Ac condensate overflowing but main drain not blocked


tommykelly
Jul 26, 2010, 08:10 AM
Overall symptom: dripping water from a plastic pipe coming out my exterior wall high up under the eave.

Probable cause: blocked main ac condensate drain resulting in condensate being diverted into a drip pan and then out into the pipe mentioned above

Usual solution: clear the main drain using a combination of (depending on severity of the blockage) water/cholorox, suction from the bottom, pressure in the top. Drain that drip pan and clean its overflow pipe while I'm at.

So I proceeded on the above basis, but haven't solved the problem. The top pipe ear the eaves -- i.e. the one that comes directly from the drip pan -- is still dripping. Here are the issues as I see them:

1. The main drain coming out of the unit in the attic -- identified because it had the little cleaning/viewing port -- was dry. Surely it should have been backed up with water in order for the condensate to then divert into the pan and then out of the pan via the pan overflow?

2. What I thought was the exit point for that main drain, out of the house but near the ground, and angled down, seems not to be. I applied vacuum suction there and got no corresponding suction up in the attic. I poured water into the attic end and nothing came out at the bottom part. I poured a lot of red food colored water into the top and blew hard. Some splashed up into an upstairs kitchen sink! I conclude that the main ac condensate is draining into the main plumbing drainage (which was partly restricted below the level of that bathroom sink, hence the slight splash when I blew).

So questions:

A. Is it credible that my main ac condensate drain (the one with the viewing port, and that comes directly from the unit and not from the drip pan) is connected to my main house drainage and not to the outside?

B. If so, what is the white plastic pipe near the ground? It is the same bore as the drain pipe in the attic, and is aligned perfectly with the attic pipe once the attic one begins its downward vertical run.

C. And so why was my overflow dripping if the main drain is clear (and dry)?

D. And why is it still dripping? The main drain is now even clearer than it was (remember, I poured a couple of liters of water into it, and it all flushed away).

Thanks.