How to Know if The AC Drain Line is Clogged

AC drain lines are the perfect breeding ground for mold, algae, and bacteria. Unfortunately, this makes them highly susceptible to clogs.

If not taken care of immediately, clogged drain lines can seriously damage your air conditioner, forcing you to pay out of pocket for repairs and replacements.

Luckily, clogged drain lines are relatively easy to fix. This article discusses everything you need to know about clogged drain lines, including how to know if an AC drain line is clogged and what you can do to fix it.  

outside ac unit

6 Major Signs of a Clogged AC Drain Line

A clogged AC line can lead to a whole host of problems. To prevent full system malfunction and risk expensive repairs, keep an eye out for these telling symptoms: 

  1. Standing Water 

One of the most obvious signs of a clogged drain line is standing water near your AC’s fan or around your outdoor unit. 

If you notice standing water near or around your unit, monitor the area for a few days to make sure it’s coming from your AC. If not, call a professional to fix the leaky areas to prevent further damage. 

  1. Dripping Water

When an AC drain line is clogged, water inevitably collects behind it. If left to overflow, you’ll be faced with a leaky AC unit.

HVAC systems drip water because of five main reasons: disconnected drain lines, clogged drain lines, low refrigerant, dirty air filter, and broken condensate pump. 

Luckily, all these circumstances have easy fixes. Disconnected drain lines can be reconnected. Dirty air filters can be cleaned. 

Low refrigerants, as well as broken condensate pumps, can be replaced. Likewise, clogged drains can be unclogged. We’ll discuss the best way of doing so in the later section.

  1. Full Drip Pan

Drip pans collect and remove excess water from the AC’s evaporator coils. Without them, AC systems won’t survive longer than a month before succumbing to water damage.

Here’s how drip pans work: as warm air passes over the evaporator coils, water droplets form and drip onto the pan located directly underneath. 

The pan then transfers the water collected from the coils directly into the drainpipe.  

A bit of water in the pan is perfectly normal. However, if it’s constantly full, this can only mean one thing: your drain pipe is clogged.

The best way to remove excess moisture from the drain pan is to use a handheld shop vacuum. You can find this at your local hardware store or online at an affordable cost. 

  1. Moldy Smell

When bacterial growth, mold, or mildew accumulates inside or outside the AC, the system may expel a stale, dingy odor.

Typically, there are three possible explanations why your AC smells musty.

One, your AC is too big for your home, preventing the system from wicking out water from the air at a good rate. 

Two, your evaporator coils are dirty. This can easily be remedied by cleaning the coils with disinfectant. Three, your drain line is clogged.

When a drain line is clogged, moisture collects in the unit, resulting in mold and bacterial growth. 

Fetid odor then travels into your air system and throughout your home via the AC or the ducts. 

The smell isn’t only unpleasant, but also potentially dangerous

Fungal spores, after all, may induce allergies, asthma, and other related health problems. 

  1. Unresponsive AC System  

If your AC unit doesn’t turn on or turns completely off at random intervals before hitting the desired temperature, this might be a sign of a clogged drain line.

Most modern AC systems are built with an auto-off mechanism that triggers when the unit detects too much water collecting in the drip pan. 

As we’ve discussed, full drip pans are caused by either a clog or obstruction in the drain line.

  1. Unexplained Water Damage 

Unexplained water damage in and around your home, such as dark, discolored walls or flooring, rust stains, and water spots near your AC’s fan or around the floor, may indicate a bad clog. 

Clogged drain lines, if left unchecked, can not only damage the AC system itself, but also your home. 

Rust stains are particularly telling, indicating that the blockage has gotten so severe that the pipes are actually corroding. 

How to Fix a Clogged AC Drain Line

Fixing a clogged AC drain line isn’t as difficult as you might initially believe. In most cases, you don’t even need the help of a professional. Here’s how to do it:

Step 1: Turn Off Your AC Unit

When we say turn off your AC unit, we don’t just mean turning the system off via remote control. We mean disconnecting the power line entirely. This guarantees the safety of both you and your AC system.

Step 2: Clean the Drain Pan

Carefully slide the drain pan out from underneath the evaporator lines. If standing water is present, remove it with a hand vac or with a rag. 

Once done, remove the pan completely and thoroughly wash it with warm water and disinfectant. This prevents the future growth of mold and algae. 

Allow the pan to dry completely before inserting it back into the unit.

Step 3: Remove Internal Debris

Insert a stiff, thin brush into the end of the drain line to remove any visible debris. Then, clean the drain line with positive air pressure or suction from a shop vacuum or wet vac. 

If not available, remove the clog with the help of a garden hose or a plumber’s snake.

Step 4: Sanitize the Drain Line

Pour about a gallon of white vinegar into the drain line. Use a funnel if necessary. This will help kill any remaining mold, algae, and other nasty growth that may cause future clogs.


As you can see, it’s super easy to unclog a drain line. If you’re facing any issues with the methods above, we recommend calling a professional to unclog the drain line on your behalf. To prevent future clogs, make sure to clean your drain line at least once every month.

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