Help with AC drain line

[txpitdog]

Found a stain on the ceiling this evening and when I went up to inspect the AC in the attic the drain pan was fine. I honestly couldn’t see where the leak occurred, but a vent or overflow from the drain line was blowing cold air. I put a rag in it to stop the loss of cooled air but anyone know what the issue is and how to fix it?




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[Atfulldraw]

where is the leak in relation to the condensate line?

that is intended to be a vent for the condensate line to prevent a vacuum from forming.

there is a LOT of discussion about where to install a condensate line vent.....without a whole lot of agreement.

[wickll]

Is it possible you have dirty coils? This can lead to water being blown into ductwork, and then it can leak out from there. Is there ductwork above the area that is wet on the ceiling?

[mikemorvan]

As stated above, various thoughts on traps and vents. But, being that the vent is there, it needs to stay open. At least replace that rag with a large piece of scrubby.

Check for leak around the furnace vent above the air handler.

[IowaHunter]

Mine exhibited the same thing and it was the condensate line going into the bathroom sink drain was plugged. The line was unplugged by the plumber but will be costing me a new kitchen ceiling paint job.

[Peta-hata]

Was the cabinet itself sweating?

[Mountaineer]

The condensate drain is insulated well in the photo, so it shouldn't be 'sweating' but look further down the pipe past the insulated section to check for condensation or loose pvc pipe connections.

The vent should generally be downstream of the trap in the condensate drain to eliminate the loss of conditioned air into the attic, or have one upstream one downstream of the trap and cap the upper one.

[double bogey]

You had air blowing out of the pvc line into the auxiliary pan. That's the emergency drain. The insulated pvc line is the main drain. That's the one that probably is clogged. Blow through coils don't require traps. They do need to go to an approved drain location, that will be trapped. Back to the leak, most techs will cut the line and use nitrogen to clear the line. The line can then be reconnected with a pvc coupling, or a rubber connector with hose clamps (this is the preferred method, as it can be used again in the event of a clog). On some coils that have the emergency drain line like the one pictured, the air flowing out can cause turbulence which can cause water to come down that line also.


All drain lines need to be vented to allow the air that is displaced by water to vent.
some times a non vented drain won't drain.


Pull through coils (which most heat pumps use) operate in a negative pressure, so they need a trap deep enough to overcome the negative pressure in the coil cabinet. Without a trap, they will hold water in the cabinet, leaking wherever it can find a way out.


Current code calls for a float switch in the system to shut the cooling down in the event of a back up. Cheaper than ceiling repairs.



AC drain 101. Use this info to clear your drain line.

[txpitdog]

I appreciate all the info. Is there anything that would cause that vent pipe to be leaking/blowing cold air into the attic?


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[tps7742]

On my unit set up like that, there is a pvc cap on that open pipe like yours. My cap you can remove it easily.

[double bogey]

The vent cap on the main line must be open to serve its purpose. You have a blow through coil, and the coil is on the high pressure side of the fan.The small amount of air venting into the attic is not an issue.

[C-beck]

Mine exhibited the same thing and it was the condensate line going into the bathroom sink drain was plugged. The line was unplugged by the plumber but will be costing me a new kitchen ceiling paint job.

This is exactly what happened to me..

[tx_basser]

drano and buckets of hot water down the drain line... i do that every couple of years to keep them open.

[CLR]

After unclogging line, a little Clorox down the vent will keep slime buildup down.

[double bogey]

I thought I would add. If you cut the main drain line, have something under it to catch the water. Blow it both directions. Some techs use a wet vac and suck it out, but I have never tried this so I wont vouch for this technique. If you don't have a float switch, you may want to look into getting one.