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Water pooling under the indoor AC unit is never a good sign. While you can fix some causes yourself in a few minutes, others require a professional right away before your equipment or flooring sustains damage.
Here are the five most common reasons an AC leaks water, what to check, and how urgent each situation is.
Cause 1: Dirty Air Filter
A clogged air filter is the easiest cause to prevent and the first one to check. When the filter blocks airflow across the evaporator coil, the coil gets too cold and freezes. When the ice thaws, water floods the drip pan faster than it can drain and overflows onto the floor.
What to check:
- Pull the filter and hold it against a bright light
- Replace it if light doesn’t pass through
- Most filters need swapping every 1 to 3 months during peak cooling season
Urgency: Low, but don’t ignore it. A frozen coil can damage the compressor if the system keeps running. Call a professional if ice returns within a day of replacing the filter. That usually means low refrigerant or a deeper airflow problem.
Cause 2: Clogged Condensate Drain Line
Your AC produces condensation as it cools the air. That water drains out through a small white PVC pipe, usually running to a floor drain or outside the home. Over time, algae and dust build up inside the line. If it gets clogged, water backs up and overflows.
What to check:
- Standing water in the drip pan under the indoor unit
- Whether water is flowing out of the outdoor end of the drain line
- Visible algae at either end
DIY fix:
- Attach a wet/dry shop vac to the outdoor end of the line for 2 to 3 minutes
- Pour a cup of distilled white vinegar down the cleanout access to prevent future algae buildup
Urgency: Address soon. Standing water can damage flooring, drywall, and ceilings below the indoor unit. Call a professional if the wet/dry vac doesn’t clear the line or water keeps returning to the pan.
Cause 3: Damaged or Rusted Drain Pan
The drain pan sits directly under the evaporator coil and catches all the condensation the AC produces. After 10 to 15 years, corrosion and cracks can develop, and water starts leaking through the pan rather than draining through the line.
What to check:
- Inspect the visible drain pan for rust, cracks, or standing water
- Feel around the base of the indoor unit for damp insulation or drywall
- Look for water stains on the ceiling below if the unit is in the attic
Urgency: Address soon. A leaking pan usually gets worse over time, not better. Call a professional. Drain pans aren’t a DIY repair. A licensed technician can replace the pan in most cases, but on older systems, a leaking pan is often an early sign that the whole unit is close to needing replacement.
Cause 4: Condensate Pump Malfunction
Some AC systems can’t rely on gravity to drain condensation. If your indoor unit sits in a basement or needs to drain upward, a small electric pump called a condensate pump moves the water to the drain line. When that pump fails, water backs up and overflows.
Signs of a condensate pump problem:
- Water on the floor near the indoor unit with no visible drain line clog
- A humming sound from the pump but no water movement
- Standing water in the pump reservoir
- The AC shutting off on its own as a safety float switch triggers
Urgency: Address within a day or two. If the pump fails in the attic, water can leak through the ceilings below. In a basement, it spreads across the floor and can damage flooring or anything stored nearby.
DIY check: Confirm the pump is plugged in and the outlet has power. If both are fine but the pump still doesn’t move water, it needs to be replaced by a licensed technician.
Cause 5: Low Refrigerant Causing a Frozen Evaporator Coil
Refrigerant runs in a closed loop and isn’t used up under normal operation. If it’s low, there’s a leak somewhere in the system. Low refrigerant causes the evaporator coil to freeze. As the ice melts, water floods the drip pan and spills over.
Signs of low refrigerant:
- Warm air from the vents
- Ice on the copper refrigerant line at the outdoor unit
- A hissing or bubbling sound near the AC
- System running constantly without reaching the set temperature
Urgency: Call immediately. Continuing to run an AC with low refrigerant can damage the compressor.
DIY check: Look for visible ice on the outdoor refrigerant line. If you see ice, shut off the AC and let the system thaw completely before restarting (this can take 4 to 24 hours).
Refrigerant work requires a licensed technician with EPA Section 608 certification. Older systems installed before 2010 often use R-22 refrigerant, which the EPA phased out in 2020. R-22 repairs are significantly more expensive than repairs on modern systems because supply is limited.
Frequently Asked Questions
Is it safe to run an AC that’s leaking water?
No. Continuing to run a leaking AC can damage the compressor, ruin flooring or ceilings, and allow mold to grow in the wet area. Shut the system off and address the cause before running it again.
How urgent is a leaking AC?
It depends on the cause. A dirty filter is a low-urgency fix a homeowner can handle in a few minutes. A refrigerant leak or a failed condensate pump in the attic is a call-a-pro-today situation. If you see water damage on ceilings or standing water near electrical connections, shut off the AC and call immediately.
Can I fix a leaking AC myself?
Dirty filters or clogged drain lines are fixes most homeowners can handle. Refrigerant, electrical, and mechanical repairs require a licensed technician.
How often should the condensate line be flushed?
Flushing the line every few months during the cooling season is a good preventive habit. Pour a cup of distilled white vinegar down the cleanout access to slow algae buildup between service visits.
Schedule AC Repair with Hero
Whether it’s a drip you noticed this morning or a leak that’s been getting worse for weeks, Hero Home Services is ready to help. We’ve been keeping Twin Cities homes comfortable since 1914. Call or text us to schedule AC repair before the leak damages the equipment or the space around it.
