Why Does My AC Unit Leak Water?

Your air conditioner doesn’t just cool the air—it also takes moisture from it.

As warm indoor air passes over the cold evaporator coil, the humidity in the air condenses into liquid water. This process is similar to how moisture forms on the outside of a cold drink.

That water is collected in a drain pan and then funnelled out of your home through a condensate drain line.

You’ll never notice this process if all the parts are clean and working properly.

But when something goes wrong, like a clog, mechanical failure or rust, the water backs up and leaks from the unit, damaging your walls, ceiling or floor.

Nothing disrupts your comfort like finding water under your air conditioner.

While it may seem alarming, a leaking AC is a common issue that is usually fixable with no need for calling a technician. The problem could, however, be beyond you, and you’d need to bring in an HVAC technician. 

6 Common Reasons Your AC Unit Leaks Water?

Let’s take a closer look at what can cause your AC to Leak—and what signs to watch for.

1. Blocked Drain Line

The most common cause of a water leak is a blocked condensate drain line.

Over time, algae, mould and dust can accumulate in the drain line and create a blockage. For this reason, the water, therefore, has nowhere to go and eventually backs up into the drain pan.

If the pan overflows, water leaks from the AC and onto your floor or ceiling.

Warning signs:

• Water pooling near the indoor unit
• Water stains on walls or ceilings
• Musty smells from the vents
• AC shuts off randomly due to a full drain pan

2. Damaged or Rusted Drain Pan

Your AC’s drain pan is designed to catch and direct water to the drain line.

However, over time, metal pans can rust and develop cracks, especially in older systems. When this happens, the pan can’t hold water properly, allowing it to drip into your home.

Watch for:

• Dripping water directly from the unit
• The AC unit is more than 10 years old
• Visible rust or corrosion on or around the pan

3. Dirty Air Filter

A clogged air filter restricts airflow, which can cause the evaporator coil to become too cold and freeze. When the ice eventually melts, the water it produces may overwhelm the drain system and cause leaks.

Telltale signs:

• Ice forming on the coil or refrigerant lines
• Weak airflow from vents
• Water leaks increase after the shut-off valve is off

4. Frozen Evaporator Coil

A frozen coil can’t absorb heat properly, which disrupts the AC’s ability to remove moisture. The moisture that collects freezes into ice, and when that ice melts, it turns into excess water that the system can’t manage.

Clues:

• Hissing or bubbling sounds (possible refrigerant leak)
• Warm air blowing from vents
• Increased energy bills without a cause
• Water dripping after long cooling cycles

5. Improper Installation

If your air conditioner was not installed correctly, the water in the drain line may not drain properly. The line must have a slight downward slope to ensure gravity pulls water out.

If it’s too flat or angled upward, water can pool and eventually spill out.

You may notice:

• A brand-new AC leaks from the start
• Recurring water problems even after cleaning
• The drain line appears bent or improperly sloped

6. High Indoor Humidity

During periods of high humidity, your AC may struggle to remove all the moisture in the air.

If the humidity is excessive, the AC can produce more condensate than the system can drain, especially if the drain pan is small or partially blocked.

Indicators:

• Water leaks during extremely humid weather
• AC runs continuously without adequate cooling
• You live in a tropical or very humid climate

What to Do If Your AC Is Leaking

Before calling a technician, there are a few troubleshooting steps you can try:

1. Turn off the system to prevent further water damage or electrical issues.
2. Check the air filter—replace it if it’s dirty or hasn’t been changed recently.
3. Inspect the drain pan for visible cracks, rust, or standing water.
4. Clear the drain line using a vacuum or a Specialised drain brush.
5. Look for ice on the evaporator coil. If it’s frozen, allow it to thaw before restarting the system.
6. Test the unit after completing the above steps to see if the leak stops.

If the problem continues or you’re unsure of what you’re seeing, it’s best to call a professional.

Preventing Future AC Leaks

Here are some proactive steps to reduce the chance of future water leaks:

• Replace air filters regularly—typically every 1 to 3 months.
• Clean the condensate drain line monthly by flushing it with a cup of white vinegar.
• Schedule annual HVAC tune-ups to inspect and clean components.
• Install a float switch, which automatically shuts off the unit if the drain pan fills with water.
• Use a dehumidifier during peak humidity to reduce the moisture load on your AC system.
• Ensure proper installation if you’re replacing or upgrading your unit—work only with a licensed HVAC technician.

When to Call an HVAC Technician

Sometimes, fixing the problem on your own won’t do it. You will need to call in an expert. Here’s when it’s time to bring it into the technician:

• The drain line stays clogged even after cleaning
• Ice keeps forming on the coils repeatedly
• You hear strange noises or detect mouldy smells
• Water damage happens frequently or spreads
• Your AC shuts off unexpectedly, or won’t turn on

A trained HVAC technician can pinpoint the root cause, fix it safely, and help you avoid more expensive repairs in the future.

Water leaking from your air conditioner may be annoying, but it’s rarely a catastrophe, especially if you act quickly. 

Your air conditioner is more than a cooling device. It plays a key role in keeping your home comfortable, dry, and healthy.

With proper care, regular inspections, and timely repairs, you can keep it running efficiently all season long and save money by preventing damage and emergency calls.