We had a new AC unit (air handler and condenser) installed a few years ago. Since then, the overflow pipes for the new unit have repeatedly backed up, causing water to leak from the corner of the air handler and causing some water damage to the wood base that holds it above the intake.
This happens every other month or so (we’re in Florida, so the unit runs a lot and has a lot of moisture to draw out of the air). I’ve now mastered the technique of clearing it using a shop vac on the outside pipe. But why should I have to? I know you’re supposed to pour something down the pipe every so often to clear them (I’ve read that both bleach and vinegar will do the job) but I’m loath to do that since if that fluid backs up it means our house will smell of vinegar or chlorine.*
In any event, I’ve lived in lots of other houses in Florida and never had this problem. Certainly not more often than once a year. What gives?
*I’m also not clear on whether I’m supposed to use dilute bleach or what.
Mold or freezing are the top two causes, especially if it’s relatively small. If it’s large enough, vermin can build nests or clog it with their bodies.
It’s like any other plumbing: it has to have a clear, sufficiently-sized run to work. If it’s too small or has tight bends or compressed connections, small amounts of gruck will plug it up. Especially true in a warm, humid environment.
The long-term solution would be to replace it with a larger pipe with a vermin screen on the outer end. Unless accessibility is a problem, it should be a simple DIY project. It’s not in any way a demanding installation; just a suitably durable pipe that has good drainage slope and will last 10+ years. No pressure, no water safety issues, just simple, no-leak mechanical operation. And a vermin screen.
Accessibility is a problem, I think. From what I can tell, the pipe appears to be the original one and runs through the foundation slab. It pops back out from the ground a few feet from the house. I don’t think it’s a vermin problem; there has never been anything alive (or formerly alive) in the shop vac. Just water and a yellowish clear gunk that looks a little like a giant’s nose blowings.
The parts that are visible are white PVC pipe. The house’s original plumbing was narrow copper pipe (we recently had a replumb) but I don’t know if they’d use the same stuff for the AC overflow.
Can I run a snake down a pipe this small? It’s only about 1 1/2" across.
Some snakes have some kind of large decloggerizer* fixed to the end, but there snakes that have removable ends or are small enough to fit down there. The small power drill or hand crank type should fit. You can get one at Harbor Freight pretty cheap, though it might fall apart after using it once.
I don’t know about vinegar (and wouldn’t advise it) but bleach works great to clear the algae that builds up. Dilute it a bit and use a funnel, so that you can entirely fill the pipe until it runs clear. They also sell A/C condensate drain tablets that you can use if you know how to/can get them into the drain pan of your air handler.
But yeah, as mentioned, you should make sure that the drain pipe always has a downhill slope to it along its full length. Any parts where it’s horizontal or even slightly uphill will accumulate standing water that WILL be a breeding ground for the algae to take hold with ferocity.
ETA: And yeah, the shop-vac method works great when it’s really clogged, but you should really use bleach periodically to retard the algae growth. The shop-vac method only culls the herd, leaving behind enough algae that it will quickly regain it’s foothold.
Copper used to be used for overflow before it shot past gold in cost.
1-1/2 inches sounds plenty big, probably one-inch or at least 3/4 inch. The “snot” sounds like a fungus.
I’d try the following, in order of effectiveness:
Snake it out. You can get (rent) small-diameter snakes. Do you know about how long the run is?
OR
Pressure-flush it from the top. Could be tricky especially if hose backwash would damage ceiling board, etc.
OR
Run about four cups of bleach mix, 1:4, down it every couple of days for a week.
Do number 3 at least once after a snake/flush to kill off any remaining fungus or mold. As recommended, try to pour such a mixture through at least once a year.
Let it flow naturally. The bleach cuts right through the algae like butter. You want to *try *to fill the *entire *pipe with bleach solution so that it gets to touch as much of the inside of the pipe as possible, until it starts draining so rapidly that you can’t keep it full.
Yes. It might even be worth plugging the outflow, then carefully pouring bleach solution until you get some backup in the drain pan, then waiting just a bit, and pulling the plug.
The obvious problem here is that an overflow/backup with the bleach could be disastrous, so you might want to make it a two-person operation: someone to plug the pipe and be ready to yank it at any moment, and someone to pour the solvent solution and be ready to yell if it backs up too fast.
If there’s no other problem, letting the full pipe soak for 10-15 minutes can’t be a bad thing.
That’s going to be a perpetual problem. See if you can find a way to add slope. Sometimes just a brick or bit of 2x4 in the right place is enough. If the section in the slab is flat, probably oh-well, but if it’s backsloped, replacing that part of the run might pay off in the long term.
Another thing you may want to consider is installing a Safe-T-Switch, which detects when the condensate pan isn’t draining and cuts off power to the A/C. That will prevent the problem of the leak continuing until it’s detected, because you’ll go to investigate why the A/C isn’t running anymore.
Well that sucks. If the pipe is oversize enough you might be able to run something smaller through to fix the slope, but it sounds like you’ll want to get into a real repair at some point.
However, as long as the output end is lower than the intake then there must be a clog of some kind, the bad slope is just making it worse.
You should be able to pull out the actual sensor part of the Safe-T-Switch that has a wire running to it, where you’ll see the floater that triggers the shutoff when it goes up. With the A/C on and running, move the floater up by hand to test whether or not it’s wired correctly and is shutting off the A/C. If it does shutoff the A/C when manually triggered, then it could be that it’s sitting at the wrong angle, or was installed incorrectly. If it’s installed in the secondary/auxiliary drain outlet, you might consider installing in-line with the primary drain, instead. It would have been good to pull out the floater unit when the primary line was completely blocked to see if there was water even arriving to the Safe-T-Switch. You might even try plugging the primary drain to artificially create a drain failure to see what’s going on with the Safe-T-Switch and if it’s even filling with water. It’s fairly easy to understand and use common sense to diagnose when you inspect it to understand how it’s supposed to work. Have a look at the installation instructions to gain some insights and consider alternative installation methods.
I think we might be getting a little beyond my mechanical abilities at this point, but I’ll give that a try this weekend. Thanks again for all the advice, guys.
