I noticed the secondary AC drain line on the side of my house had a slight drip a few days ago. This caught me by surprise as I am typically pretty good about putting bleach down the primary drain to keep it from developing any clogs.

I went into the attic to investigate and found a small amount of water in the secondary drain pan. I have an open standpipe downstream of a block valve and just upstream of the trap where I am able to see condensate running through the primary drain. The condensate appeared to be flowing ok when the unit was running. I went ahead and added some bleach followed by pouring a few cups of very hot water down the standpipe.

The next day i checked again and the issue was the same. This time I used a long zip tie to try and break up any algae that may have developed in the trap. Checked again the next day and issue was the same. This time I lugged a shop vac into the attic and using a piece of garden hose duct tapped to a shop vac attachment I vacuumed out the primary drain line back towards the unit as well as towards the trap.

None of these techniques appear to have remedied the slow drip I have coming from the secondary turndown into the secondary pan.

Can someone provide some insight into why this may be happening? This is a Trane unit that is only a few years old. Thanks for any input you may have.

Do you have rodents in your attic? Check to make sure something hasn't been eating or moving the insulation around the cooling coils in the attic. Sounds like warm-moist air has found a way to access your coils and is condensating out. Also make sure that none of the intake pipes into the attic AC have any leaks that would pull in attic air.

Primary tie in under a sink?

Primary drain ties into master bath toilet. The part that I don't understand is why I am I getting a drip of condensate from the secondary drain when it appears that the primary drain appears to be functioning fine. This doesn't appear to be an issue of the air handler sweating. The water is coming from the pvc turndown (secondary drain pipe that leaks into secondary pan). Hopefully my terminology here is making sense.

aarontx said:

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Primary drain ties into master bath toilet. The part that I don't understand is why I am I getting a drip of condensate from the secondary drain when it appears that the primary drain appears to be functioning fine. This doesn't appear to be an issue of the air handler sweating. The water is coming from the pvc turndown (secondary drain pipe that leaks into secondary pan). Hopefully my terminology here is making sense.

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I don't buy it. I think you still have a problem with the primary drain line. You need to snake it all the way out - verify it's clear all the way through.

Use the opposite of a vacuum cleaner. If you have one use an air tank and blow the line clear.

Forgot to mention that I had also used an air gun and wet towel to try and get a good seal to blow it down. I'm beginning to wonder if the restriction is more upstream near the unit itself versus being downstream (the trap and pipe that leads to master bath). When I was pouring the hot water down the drain it appears to go down no problem.

Mathguy64 said:

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Use the opposite of a vacuum cleaner. If you have one use an air tank and blow the line clear.

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Just be sure you're only blowing downstream. You don't want to push gunk upstream into your A/C.

I have seen drain issues when the filter is very dirty and the fan is not in auto. Pressure in cabinet to hold water back enough to overflow in pan in the unit.

Ours drains into a bathroom sink. Noticed the sink wasn't draining well this weekend and cleaned out a good bit of gunk.

What's a good way to prevent the gunk build up in the sink drain?

This thing works pretty well for getting an air hose to drain seal

https://www.amazon.com/dp/B08FMWPL2Z?psc=1&ref=ppx_yo2ov_dt_b_product_details

Had a similar issue and couldn't get a snake through due to where it was located. Was able to determine line was clogged between sink and toilet where line connected. Was about to call a plumber when my FIL suggested this option. Worked amazingly well. As you mentioned, just make sure you have all holes covered to allow pressure to push through the line and unclog.

https://a.co/d/8P7iH6g

My uncle tried that and it worked spectacularly. Cleared the upstairs clog and blew black sludge all over the downstairs kitchen.

Edit to add that when I had a similar issue, I paid a couple hundred bucks for a plumber to come out. I've seen too much of my plumbing to trust that kind of pressure testing through the entire house.

Milwaukees Best Light said:

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Primary tie in under a sink?

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This. I had to open up my pipes under the sink and clean those out. It's the wife bathroom sink so all kinds of hair and crap in there.