Why Is My AC Leaking Water?

How an AC Makes Water in the First Place

Your air conditioner removes heat and moisture from indoor air. Warm, humid air passes over a cold evaporator coil, the water vapor condenses into liquid, and that condensate is supposed to leave through a drain pan and a drain line. A small, steady drip at the outdoor termination of the drain line is normal during cooling. Water inside the home, pooling near the air handler, staining ceilings, or dripping from vents is not normal and needs attention.

Normal Condensation vs. Problem Leaks

Normal: clear water flowing from the condensate drain outdoors, especially on humid days. Problem: water overflowing the indoor pan, leaking at the air handler, attic, closet, garage, or furnace room; water marks on ceilings; rust; moldy odor; gurgling or bubbling sounds in the drain. If the leak is inside, turn the system off to prevent further damage and start simple checks listed below.

The Most Common Reasons an AC Leaks Water

• Clogged condensate drain line: algae, dust, drywall dust, pet hair, or scale block the line or the trap, backing water into the pan.
• Disconnected, cracked, or sagging drain line: a loose fitting or a line with dips traps water and overflows.
• Dirty air filter or blocked return: restricted airflow lets the coil get too cold, ice forms, then melts quickly, overwhelming the pan.
• Low refrigerant charge: low pressure makes the coil freeze; thawing floods the pan. Low charge often means a refrigerant leak that must be found and fixed.
• Rusted or undersized drain pan: corrosion or a pan without enough capacity or slope spills water.
• Improper installation or leveling: if the air handler or pan is not pitched toward the drain (about 1/8 inch per foot), water stands and spills.
• Missing, failed, or miswired float switch: safety switches are meant to shut the system down when water rises; if missing or faulty, leaks go unchecked.
• Condensate pump failure: in condos, basements, and attics, a small pump pushes water up to a drain; if the pump or check valve fails, water backs up.
• Inadequate insulation or sweating: warm, humid air can condense on uninsulated metal surfaces near the unit and drip, mimicking a leak.
• Duct leakage or unsealed return: hot attic air leaks into the return, raising humidity at the coil and creating excess condensate.
• Oversized or short-cycling systems: frequent starts and stops reduce the unit’s ability to move water continuously to the drain.
• Heat pump or rooftop unit issues: during certain modes, exterior condensate may look heavy; indoor water is still a red flag.

Immediate Steps to Reduce Damage and Stay Safe

1. Turn the thermostat to Off and set the fan to Auto. If water is actively dripping, switch the dedicated breaker off as well.
2. Protect your home: move electronics and valuables, place a container under drips, and gently mop or towel puddles to prevent slip hazards.
3. Replace a dirty air filter. A clean filter restores airflow and may prevent refreezing when the system is restarted.
4. Inspect the visible drain line outside. If there is a cleanout cap near the air handler, you can carefully remove it and pour a small amount of warm water or white vinegar to see if it flows. Do not force water into a fully clogged line.
5. Do not open sealed panels, bend copper lines, or chip ice from the coil. Avoid mixing chemicals like bleach with other cleaners; fumes can be dangerous and can damage metals.
6. Document what you see. Take photos of the leak, the area affected, and any ceiling or floor damage. Many home insurance, landlord, or HOA policies require licensed HVAC findings for water-damage claims; unqualified DIY work can jeopardize coverage.

When a Leak Signals a Bigger Problem

Repeated coil icing, hissing or bubbling sounds, unusually high energy bills, water stains returning after a quick drain-line flush, or the smell of mildew indicate a deeper issue such as a refrigerant leak, negative building pressure, or poor installation geometry. In Southern California, many systems are in attics; local code typically expects a primary drain, a secondary emergency pan and drain, and a working float switch. If any of those are missing or defeated, even a minor blockage can cause ceiling damage and mold growth.

Why ACs Leak More Often in Southern California

Our climate swings from coastal humidity and marine layers to hot, dry heat. Coastal salt and fine dust can coat coils and drains. Wildfire ash and construction dust accelerate drain clogs. Attic installations in older homes may have marginal access, long horizontal drain runs, or insufficient slope. Heat waves drive long runtimes that reveal marginal drainage. All of this makes regular inspection and correct pitch, trapping, and venting of drain lines especially important across Los Angeles County and nearby areas.

Preventive Maintenance That Actually Works

• Change filters on schedule. In peak cooling season, check monthly and replace as needed.
• Flush the drain line with warm water or distilled white vinegar; avoid harsh chemicals that corrode metals.
• Vacuum the drain line from the outdoor end with a wet/dry vacuum to remove slime and debris.
• Verify slope: the pan and drain should be pitched toward the outlet. Correct sags with proper supports.
• Test the float switch annually. Confirm it shuts the system off when the pan fills.
• Clean the evaporator coil when needed. A clean coil condenses and drains predictably.
• Insulate cold suction lines and nearby metal to reduce sweating.
• Inspect primary and secondary pans, especially in attics, for rust, cracks, or standing water.

Professional Diagnostics You Cannot Safely Replicate

• Measuring system static pressure, temperature split, superheat, and subcool to see if airflow or charge is at fault.
• Leak detection and nitrogen pressure testing to confirm and locate refrigerant leaks before recharging.
• Camera inspection of long drain runs and rebuilding traps and vents to meet code and manufacturer guidance.
• Re-leveling air handlers, adding emergency drain pans, and installing or wiring float switches correctly.
• Manufacturer-specific controls and defrost logic checks. Our engineering team has trained at manufacturers’ plants including Fujitsu in Japan, Mitsubishi Elektrik in Thailand, Midea in China, Gree in China, and Hier in China, so we follow factory geometry and drainage best practices.

About #1 AC Guys

#1 AC Guys is a family HVAC business rooted in Los Angeles, Southern California. Our family of engineers is now in its fourth generation, with 80+ years of engineering experience applied to residential and commercial HVAC, especially large and complex projects. Our mission is healthy air at home for healthy living. We serve Los Angeles County and nearby areas including Orange County, Ventura County, and Western Riverside County. Examples include Los Angeles, Long Beach, Pasadena, Santa Clarita, Glendale, Anaheim, Irvine, Huntington Beach, Santa Ana, Fullerton, Thousand Oaks, Camarillo, Ventura, Oxnard, Corona, Riverside, Temecula, and surrounding communities.

Quick Answers to Common Questions

• Is a little water outside normal? Yes, a steady drip from the condensate drain outside is normal in cooling mode.
• Can I pour bleach down the drain? Use distilled white vinegar or warm water instead; bleach can damage metals and produce dangerous fumes when mixed.
• My ceiling sagged. What now? Turn the system off, protect the area, and document the damage. Many insurers require a licensed HVAC report to process claims.
• Could the leak be refrigerant? Refrigerant does not drip like water. Water leaks often come from condensate or melting ice due to airflow or charge issues.
• After I cleared the drain, it leaked again. Why? Recurring clogs often mean improper trap, lack of venting, no float switch, biofilm growth, or freezing from charge/airflow problems.

Key Takeaways

• Water forms naturally in cooling mode, but it must drain through a clean, properly pitched system.
• Clogs, freezing, failed pumps or switches, rusted pans, and poor installation are top causes of indoor leaks.
• Shut the system off, protect your home, try safe checks like filter replacement and gentle drain clearing, and document damage.
• Because water damage claims often require licensed HVAC findings, and some fixes involve refrigerant, electrical, or code work, qualified professional diagnosis is essential for a lasting solution.