Why Is My AC Leaking Water? Causes, Fixes, and What to Do Right Now

An AC water leak can trace back to a clogged condensate drain line, frozen evaporator coils, a dirty air filter, or a cracked drain pan. When your system cannot properly drain condensation, water backs up and overflows into the home. This guide walks you through each cause, how to confirm it, and exactly what to do next.

Chill out—we’ve got your cooling covered.

Protection that keeps your home comfortable
when temperatures soar.

Explore AC Coverage

What Causes an AC to Leak Water?

Most AC water leaks share a common thread: condensation that cannot drain properly backs up and escapes the system. The six causes below cover the overwhelming majority of service calls. Each section includes how to confirm the problem, DIY fix steps, and when to hand it off to a professional.

1. Clogged Condensate Drain Line

According to Trouble Free Inc., clogged condensate drain lines account for approximately 80% of AC water leak service calls. Your AC pulls humidity from indoor air, and that moisture collects in the condensate drain pan before draining out through a PVC drain line. Over time, algae, soot, dust, and grime build up inside that line and block the flow.

When the drain line clogs, water overflows the pan and drips into your home. This is the first place to check.

How to confirm it: Look for standing water in the drain pan under the air handler. If the pan is full and the line feels wet but nothing is draining, the line is clogged.

DIY fix steps:

1. Turn off the AC at the thermostat and the breaker.
2. Locate the condensate drain line, typically a white PVC pipe near the air handler.
3. Attach a wet/dry vacuum to the end of the drain line and run it for 1 to 2 minutes to pull the blockage free.
4. Mix equal parts white vinegar and water, about one cup of each, and pour the solution into the drain line access port.
5. Wait 30 minutes for the vinegar to break down algae and buildup.
6. Flush the line with clean water to clear the residue.
7. If water continues to back up, call a licensed HVAC technician.

Cost range: Professional drain line clearing typically runs $150 to $300.

A note on condensate pumps: Basement and lower-level AC systems cannot rely on gravity to move water to a drain. These installations use a condensate pump to lift water up and out. If your system is below grade and you find no clog in the line, inspect the condensate pump. A failed float switch or burned-out pump motor will cause water to back up just as a clog does. Pump replacement typically costs $250 to $500 installed.

2. Frozen Evaporator Coils

The evaporator coil sits inside your air handler and absorbs heat from indoor air. If airflow across the coil is restricted, or refrigerant levels drop too low, the coil can drop below freezing and ice over. When the system cycles off, that ice melts and overwhelms the drain pan.

How to confirm it: Turn off the AC and open the air handler access panel. Ice on the coil or coil fins confirms the problem.

DIY fix steps:

1. Turn the system off and set the fan to "on" to accelerate thawing.
2. Place towels around the air handler to catch melt water.
3. Once the ice has fully melted (typically 2 to 4 hours),inspect the coil fins for dirt and debris.
4. Gently wipe the fins with a damp cloth if they appear coated in dust or grime.
5. Replace the air filter before restarting the system.
6. If the coils freeze again within a day or two, the cause is likely low refrigerant, which requires a licensed technician.

Cost range: Coil cleaning runs $100 to $400. Refrigerant-related repairs vary depending on the cause of the loss.

3. Dirty or Clogged Air Filter

A dirty air filter restricts airflow across the evaporator coil. Restricted airflow drops coil temperature below freezing, the coil ices over, and when the ice melts, water leaks from the unit. The fix is simple, but many homeowners wait too long between changes.

Air filters should be replaced every one to three months. In homes with pets, high dust levels, or poor outdoor air quality, monthly replacement is appropriate.

How to confirm it: Pull the filter. If it is visibly gray, packed with debris, or you cannot see light through it, it needs replacing.

DIY fix steps:

1. Turn off the AC.
2. Locate the filter slot at the return air vent or inside the air handler.
3. Remove the old filter and note the size printed on the frame.
4. Install a new filter in the correct airflow direction (marked by an arrow on the frame).
5. Restart the system and monitor for ice or continued leaking.

Refer to our guide on taking care of your AC unit for a full filter maintenance walkthrough.

Cost range: Filters cost $5 to $40 depending on type. This is a DIY task with no labor cost.

4. Cracked or Corroded Drain Pan

The condensate drain pan sits directly under the evaporator coil to catch dripping condensation. In older systems, this pan can rust through or develop pinhole cracks. The pan still collects water, but it leaks through the damaged area before the water ever reaches the drain line.

How to confirm it: Use a flashlight to inspect the pan. Look for rust staining, visible cracks, or standing water that is not draining through the line. To check for pinhole leaks, dry the pan completely with a cloth, then watch for water seeping through the metal rather than draining out.

DIY fix steps:

1. Turn off the AC.
2. Remove standing water from the pan using a wet/dry vac or sponge.
3. Apply waterproof drain pan sealant as a temporary fix for minor cracks.
4. Schedule replacement with a licensed technician for a corroded or structurally compromised pan.

A corroded drain pan is often a signal that other components in an aging system are approaching end of life. Have a technician assess the full system while addressing the pan.

Cost range: Drain pan replacement typically runs $400 to $700 installed.

5. Low Refrigerant Levels

Your AC’s refrigerant circuit is a closed system. Refrigerant does not get "used up" over time, so a low reading always points to a leak somewhere in the system. Low refrigerant reduces pressure in the evaporator coil, causes it to ice over, and leads to the same melt-water leak described under cause two.

How to confirm it: Signs include warm air from the vents, a hissing or bubbling sound near the refrigerant lines, and a system that runs constantly without cooling effectively. A technician must confirm with a pressure test.

Important: Refrigerant handling requires EPA Section 608 certification. Homeowners cannot legally or safely purchase, handle, or add refrigerant themselves. If low refrigerant is the cause, call a licensed HVAC technician. Attempting a DIY fix can void your warranty, violate federal law, and pose safety risks.

Cost range: Refrigerant leak repairs vary widely based on the location and severity of the leak.

6. Improper Installation or Servicing

A drain pan or drain line that is not properly leveled during installation will allow water to pool in the wrong spot and overflow. An installer who undercharges refrigerant creates a low-refrigerant condition from day one.

How to confirm it: Installation issues typically surface within the first few weeks of a new system or following a recent service visit. If your system had operated without a problem for years before a leak appeared, look at the other causes first.

What to do:

• Contact the installing contractor and request documentation of the original installation, including refrigerant charge levels and drain line slope verification.
• Ask specifically whether the condensate drain line was pitched correctly (the line should slope at least one quarter inch per foot toward the drain).
• Request a callback inspection if the issue appeared within 30 days of installation or service.

If the installation is under warranty, the contractor should correct the issue at no charge.

Signs Your AC Is Leaking Water

Some AC water leaks are immediately obvious. Others build quietly over days or weeks. Watch for these warning signs:

• Puddles and drips: A pool of water under or around the indoor unit is the clearest indicator. You may also notice dried water stains where liquid has evaporated. Do not assume a dried stain means the problem has resolved; it usually means the leak is intermittent.
• Water near electrical components: Water dripping toward the air handler’s wiring, the breaker panel, or wall outlets is a safety hazard, not just a maintenance issue.
• Active dripping from the ceiling or wall: Water coming through a ceiling or interior wall below an upstairs air handler indicates the drain pan has overflowed significantly.
• Inefficient cooling: A system that runs longer to reach the set temperature, or one that causes an unexplained spike in energy bills, may be compromised by a leak affecting the coil or refrigerant circuit. See our list of the most common air conditioner problems for additional context.
• Mold or mildew odor: A musty smell near vents or the air handler often traces back to moisture accumulation from a slow or intermittent leak.
• Corrosion on the unit: Rust or oxidation on the air handler cabinet or drain pan suggests prolonged moisture exposure and a leak that has been active longer than you may realize.
• Low refrigerant indicators: If refrigerant is leaking rather than water, the system will still underperform. A sealed system that loses refrigerant has a breach that requires immediate professional attention.

Is an AC Water Leak an Emergency?

An AC water leak becomes an emergency when water reaches electrical components, actively drips through a ceiling or wall, or when visible mold growth is present near the unit. In those situations, turn off the AC at the thermostat and cut power to the unit at the breaker immediately. Minor condensation dripping in humid weather outside the home is typically not urgent, but any indoor leak that is active, growing, or near wiring should be treated as a priority repair.

The EPA identifies HVAC condensate leaks as a significant indoor moisture source and a leading contributor to mold growth. Mold can begin colonizing wet drywall and insulation within 24 to 48 hours of water exposure. That timeline is short enough that an active leak into a wall or ceiling warrants same-day attention.

When to Turn Off Your AC Immediately

Stop running the unit and cut power if any of the following conditions are present:

• Water is near electrical components: If condensate has reached the air handler’s wiring, control board, or any nearby electrical outlet or panel, cut power to the unit before touching anything. Water and electricity present a serious shock and fire hazard. Review electrical hazards from water damage for additional safety guidance.
• Water is actively dripping through a ceiling or wall: This indicates the drain pan has overflowed substantially and structural or mold damage may already be underway.
• Visible mold is present: Mold near the unit, drain pan, or on surrounding surfaces means moisture has been accumulating long enough for colonization to begin.

Can I Still Use My AC If It’s Leaking?

Running a leaking AC risks mold growth, ceiling and wall damage, and electrical hazards that can worsen quickly. Turn the unit off until the cause is identified and repaired. If the leak is minor condensation dripping outside the home at the condensate line exit point, brief continued use may be acceptable, but the issue should still be diagnosed and resolved promptly. When in doubt, turn it off.

 

How Much Does It Cost to Fix an AC Water Leak?

Repair costs range from under $10 for a filter replacement to several thousand dollars if a leak has caused mold or structural damage. The table below reflects typical ranges for the most common repairs.

 

 

These ranges reflect parts and labor in most U.S. markets. Costs can run higher in high cost-of-living areas or for systems that are difficult to access.

AC Water Leaks by System Type

Not all AC systems leak for the same reasons or in the same locations. Here is what to know by system type.

Central Air Conditioner

Central systems have an indoor air handler, an outdoor condenser unit, and a network of ductwork. Water leaks almost always originate at the indoor air handler, where the evaporator coil and condensate drain pan are located.

Common causes specific to central systems include long or horizontal drain line runs that are more prone to clogging, failed float switches that should shut the system down when the pan fills, and drain pans that can rust through in systems that are 10 or more years old.

If your central AC is not cooling and you notice a leak, suspect a frozen coil or refrigerant issue first.

Window AC Unit

Window units are self-contained, and a small amount of water dripping from the back of the unit to the outside is normal and expected. The unit is designed to drain condensation away from the home.

A window AC leak becomes a problem when water drips into the room rather than outside. This usually traces back to one of three causes: the unit is not tilted slightly toward the outside (the rear should sit about half an inch lower than the front to direct drainage outward); the drain holes at the base of the unit are clogged with debris; or the unit has been installed in a window that does not allow for proper pitch. Tilt correction and drain hole cleaning are both DIY tasks.

Ductless Mini Split

Mini split systems have an indoor air-handling head unit mounted high on the wall and a small condensate drain line that runs to the outside or to a nearby drain. Leaks from the indoor head unit are typically caused by a clogged drain line, a disconnected drain hose fitting, or a frozen evaporator coil from low refrigerant.

Because the head unit is wall-mounted, water from a blocked drain line often runs behind the unit and down the wall before it becomes visible. If you notice water stains on the wall below the head unit, check the drain line for kinks, clogs, or a disconnected fitting at the back of the unit.

What NOT to Do When Your AC Is Leaking

Avoiding these mistakes can prevent minor leaks from becoming expensive repairs.

• Do not keep running the unit when water is actively pooling. Continued operation while water is accumulating accelerates mold growth, increases ceiling and wall damage, and can push water toward electrical components.
• Do not pour undiluted bleach into a PVC condensate drain line. Concentrated bleach can degrade PVC fittings over time and may void manufacturer warranties on certain systems. Use a 50/50 vinegar and water solution instead.
• Do not assume a dried water stain means the problem has resolved. A dried stain means the leak was active long enough to leave a mark and then paused. The underlying cause is still present.
• Do not attempt to handle refrigerant yourself. Adding, recovering, or transferring refrigerant without EPA Section 608 certification is a federal violation, not a DIY gray area. If low refrigerant is the cause, stop at diagnosis and call a certified technician.

How to Prevent AC Water Leaks

A consistent maintenance routine eliminates most AC water leak causes before they develop. Key tasks:

• Replace the air filter every one to three months. High-traffic homes, homes with pets, or homes in dusty climates should change filters monthly. A clean filter protects the evaporator coil from icing and protects the blower motor from strain. Follow a regular AC maintenance schedule to stay on track.
• Inspect and flush the condensate drain line twice per year. Use the vinegar flush procedure described under cause one. Spring and fall are good timing anchors, before and after peak cooling season.
• Check the condensate drain pan annually. Look for rust, cracks, and standing water that indicates a slow drain. Catching a corroded pan early avoids a more expensive water damage event.
• Inspect or test the condensate pump if your system uses one. Pour a small amount of water into the pump reservoir and confirm it activates and drains. A pump that does not respond needs service before the cooling season begins.
• Schedule a professional inspection annually. A licensed HVAC technician will check refrigerant levels, clean the evaporator coil fins, verify drain line slope, and identify developing issues before they become emergency repairs. This single step addresses the causes that homeowners cannot easily self-diagnose.

For a full seasonal checklist, see our guide on taking care of your AC unit.

When a Home Warranty Covers AC Water Leak Repairs

AC water leak repairs can run anywhere from $150 for a drain clearing to $3,000 or more if water damage has reached drywall or triggered mold remediation. A home warranty with HVAC home warranty coverage protects you from those out-of-pocket costs when a covered component fails. Liberty Home Guard’s home warranty plans include robust HVAC coverage, so when your AC needs service, you file a claim rather than absorb the full repair bill. Call (866) 983-0874 to review your coverage options.

Chill out—we’ve got your cooling covered.

Protection that keeps your home comfortable
when temperatures soar.

Explore AC Coverage