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Today we’ll talk about what an AC drain line does, what can cause it to clog, and how to tell that your AC drain line is clogged.  

Your air conditioner does a lot of important things for your home. Beyond keeping it cool or at a comfortable temperature, it also serves the function of removing humidity from the air. This is a really important component of keeping the air in your home comfortable – not just cool. But the moisture that’s being pulled from your air has to go somewhere… Have you ever wondered where? That moisture gets drained out of your A/C unit and away from your home by the condensate drain line. It’s a really important component of the entire A/C unit. And, unfortunately, it’s something that can become clogged, causing a fluid backup that can create leaks, leave standing water on or near your unit, and lead to serious issues. 

What is an AC Drain Line?

The A/C drain line is a really important component of your entire A/C unit. Unfortunately, a lot of people don’t know what it does – they, therefore, don’t know what’s happening when it becomes clogged. So, what is an A/C drain line, and how does it work? 

Your air conditioner controls the humidity in the air of your home by extracting moisture from the air using the condensate coils. The moisture condenses on those coils, turning it into condensate water. That water gets funneled out of the A/C system and out of your home through the AC drain line (also referred to as the condensate drain line or condensate drain pipe). It’s a really important component of the A/C unit: without this drain line, water pulled out of the air would have nowhere to go. It would stay in and around your unit, and that pooled water around your A/C unit could cause some serious problems. 

Let’s talk about what can happen if a drain line gets clogged, and why that might occur. 

What Causes A Clogged AC Drain Line?

There are five big things that can make your ac condensation drain line clogged. They are:

Rain and storms

Heavy rain can sometimes get into your drain line, creating excess water that ultimately backs up and leaks into your unit. Heavy storms could also cause mud, sludge, or debris to make its way into your drain line, causing a clog. Also, if a storm is creating a significant increase in the humidity in the air, this could create excess condensate which might backup your drain line. 


Especially in the fall, make sure to watch out for leaves blocking the drainage of your A/C drain pipe. A trained HVAC technician can check this for you if you’re unsure where to look.


It does not just leave: a lot of odd things can end up blocking your drainage pipe, causing a blockage. Look for things like mud, dirt, rocks, twigs, or even animal hair.

Extreme temperatures

If your area is suddenly hit with a heatwave, it could create complications for your A/C unit. An A/C unit that’s forced to work overtime in extreme heat could end up getting its coils frozen. When this happens, and the coils then melt, that excess water flooding the drain pipe all at once can create a water backup. But you should also watch out for unexpected cold snaps: hail or ice can block your drainage system just as easily as leaves and dirt can. 

Flooding in your area

This onslaught of excess water could overwhelm your drainage system, causing water to back up into your A/C and home

AC Drain Line Clogged Symptoms

Now we know what can cause a drain line to become clogged. But just because your system is clogged doesn’t necessarily mean you’ll know right away. How can you tell that a clog has occurred? Let’s talk about what to look for so you can be prepared and respond accordingly. 

There’s a musty, moldy smell near your indoor unit or in the air from the registers/vents

Follow your nose: if an unusual musty or moldy smell is coming from your unit, don’t ignore it. It likely means that there’s sitting water somewhere on or near the unit that you just can’t see. Possibly, the water is getting clogged in the drainpipe but hasn’t yet backed all the way up to your system. Either way, you’ll need to address that clog quickly so that water can continue flowing. 

You see standing water near the indoor unit

Standing water is a pretty dead giveaway that something’s gone wrong with your drainage system. If you see standing water, act very quickly. Turn off the A/C unit immediately and then go ahead and clean up the water to the best of your ability. A small amount of water can be mopped up with towels, but a lot of water may need to be sucked up with a shop vac. Then, call your A/C technician to come to diagnose the problem and find out if there’s a clog. 

There’s water damage in areas near the indoor unit

Even if there’s no standing water near your unit currently, you’ll be able to tell if there ever has been if you see evidence of water damage. Water damage on wood floors or drywall usually looks like a yellowish stain. If the walls or baseboards around your unit are at all soft or spongy, this is another sign that water damage has occurred. Don’t wait until the damage gets worse – call your HVAC technician the minute you see the signs. 

Your AC system is not cooling your home

If your A/C just isn’t keeping up anymore, you know something is wrong. It’s quite possible that something is a clog in your drainage system (although it could also be other things). Have an HVAC specialist come out quickly so they can diagnose the problem and find a solution. 

Your AC system shuts down or doesn’t turn on

If the system shuts off entirely, a very major situation may have occurred. It’s possible that a clog has caused water to back up into the system and has damaged the electrical components of the unit. Unfortunately, this is a very serious issue and something that a trained technician will need to diagnose. Replacing the unit may – unfortunately – be in order. 

Steps to Take When Your Drain Line is Clogged

Dealing with a clogged drain line is never fun, but the good news is that there are ways you can fix the issue yourself.

  • First, if you see any standing water (or evidence of standing water), turn off the A/C unit immediately. Clean up the water that you see, either with a towel or using a shop vac. Then, you can set to work investigating the issue. 
  • If you do have a shop vac, go ahead and use it to clean out the drain pipe. Start with an empty shop vac – that way you can tell if anything’s getting pulled out of the drain pipe.
  • If that’s not the issue, be sure to check the end of the drain pipe where it drains into the city sewer system. Look for leaves, mud, or other debris that might be blocking the way.
  • Finally, if the clog cannot be found with either a shop vac or by checking the pipe exit, it may be time to place a call to an HVAC specialist. 

Call AC Care for Help With Your Clogged Drain Line

The talented folks at A/C Care know exactly what to look for when investigating a potential clog. They’ll have the tools and know-how to diagnose the situation quickly, and can offer you a number of solutions so that you can get back to enjoying cool air. Give them a call if you suspect there’s an issue.

Remember that if you see standing water, see water damage near the unit, have a system that’s not working well or is shutting off, or can smell a musty smell coming from your unit, these are all signs that a clog may be occurring… and that you need to act quickly. A trained technician will also be able to consult with you on ways to prevent future clogs. For example, did you know that changing out your filters regularly can help prevent clogging?

So don’t wait: if you sense that your system may have a clog, contact the talented team at A/C Care today! 

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