How to Clean a Clogged AC Condensate Drain Line

Last week our upstairs HVAC unit stopped working. My husband climbed up into the attic to troubleshoot, and quickly determined that we had a clogged condensate drain line.

That’s the line that your air conditioner uses to get rid of all the humidity that it pulls from the air. When everything is working properly, condensation runs down the drain line and exits outside your house.

But that drain line is pretty small, so it doesn’t take much for it to become clogged. Sediment, algae, mold and insects can all clog it up. When that happens, water backs up into the drain pan under your air handler. If you have a newer unit, a sensor will shut your unit off, alerting you to a problem. If you have an older unit, you may not know you have a problem, until the pan overflows and causes water damage to your home.

So how do you fix the problem? You could call an HVAC company to come clear the clog, but if you want to save money, this is definitely a problem that you can handle yourself.

Here’s What You Do:

1. Turn off your AC unit at the thermostat and at the breaker.

2. Locate where the drain line exits your house, and make sure it isn’t clogged by an insect nest or something obvious. The exit point is usually (but not always) near the condenser unit. It’s possible that you may not have an outdoor exit point at all. Our upstairs HVAC unit runs to our bathroom drain.

3. If that doesn’t solve the problem, locate the drain line access point near your indoor air handler. Remove the plug. Then, attach the suction hose of a wet vac to the line, and try to suck the clog out. For this to work well, you need to make a tight connection between the hose and the line. We started by putting the vacuum hose over the drain line. That pulled some of the clog out, but it didn’t create enough suction to pull all of the clog out.

So, we tried a Lint Lizard hose attachment that we had on hand. It’s intended for cleaning out dryer vents, but it worked perfectly for this. A Vaccuflex vacuum attachment would serve the same purpose, and is easier to find. What’s good about both of these is that they allow you to stick your hose in past the T, so that you’re sucking air/water from the condensate line, rather than from the air handler.

Here’s the crud that we sucked out of our line on our fourth (and final) attempt.

4. If the drain line is still clogged, trying sucking the clog out from the exit point. It may just be further down the line than you’re able to reach from the access point.

5. If, at this point, you still haven’t made any progress (or much progress), pour a cup of white vinegar into the access point, and allow it to sit for a few hours. This will kill any algae or mold that’s present, and help to break up the clog. Then, try sucking the line out again.

Be sure to place a bucket under the outdoor exit point before you add vinegar to the line. If it drips onto plants, it may kill them.

6. Still no luck? Then, you may want to try snaking out the line. You may not clean out your clog on the first attempt, but if you stick with it, you should be able unclog it without a call to an HVAC repairman.

How to Prevent Future Condensate Drain Clogs

Once we removed the clog, we flushed out the line with vinegar. I plan to make this a yearly maintenance task now. If you live somewhere humid, you may find that you need to do this more often.