Central Air Conditioning Condensation Drain, Trap and Cleanout

Last summer I began having humidity problems in my house, even with the air conditioning running. A quick inspection of the fan coil unit showed that the evaporator condensate pan was not draining properly, leaving the pan full with water. As the fan circulated ventilation air when the air conditioner was not running, it would simply evaporate the water in the condensate pan, and bring it back into the house.

My condensate drain was constructed of 3/4" CPVC pipe, and the installer put in a simple P trap made of 90 degree elbows, as shown below. I tried flushing out the P-trap by putting a hose nozzle inside the fan coil unit - very awkward, and not very effective. I had to find a better way of cleaning out the trap.

Condensate drain made from 3/4" CPVC pipe and 90 degree elbows
A second issue with this drain was that there was no slope added to the pipe when it hit the floor and ran for about 20 feet.

Drain runs about 20 feed along the floor slab to a floor drain
To be able to get in and clean out the P trap, I cut the trap out of the system, and reinstalled it with two CPVC union fittings. I started by installing the top union, to be able to measure the down pipe on the other side to get the right height for the second union. When I got the P-trap removed, it was completely gunked up with scale, rust from the condensate pan, and spider webs. It was easy to clean out once removed.
Installing CPVC union fitting on the trap

Here's the finished trap with two unions installed. 
I also corrected the slope of the pipe running along the slab, to avoid water pooling in the flat runs, evaporating, and leaving scale. 

Shimming the drain pipe to get the correct slope 
Adding shims under the pipe straps to correct the drain slope.
All told, this project took a couple of hours, but it should reduce the amount of maintenance required to keep the pipe flowing, and greatly simplify cleaning out the trap. If you're putting in a new drain, consider putting in the union fittings right from the start. They're not expensive, about $4 or $5 for a 3/4" union.

Water fllowing through the drain line again.


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