Why Is My AC Leaking Water Inside My House? A Lowcountry Diagnostic Guide
Water pooling around your indoor AC unit comes from one of five places: a clogged condensate drain line, a cracked or rusted drain pan, a frozen evaporator coil that's thawing faster than the drainage system can handle, a disconnected drain line, or a failed condensate pump. In high-humidity coastal South Carolina, AC systems pull a meaningful volume of moisture out of the air every day, and any of those five points blocking that drainage path puts water on your floor. Coastal Carolina Comfort sees this failure pattern across Summerville, Charleston, and the surrounding Lowcountry every summer — and most causes are single-visit repairs.
The fast move when you see standing water near the air handler: turn the AC off at the thermostat, place towels around the unit, and stop the leak from spreading into drywall or flooring. The diagnostic below is the order Coastal Carolina Comfort techs use to identify which of the five causes you're dealing with, in order of how often each one shows up on actual service calls in the Summerville and Charleston markets.
Why Lowcountry homes see more AC water leaks
An air conditioner doesn't just cool air — it removes moisture from it. The evaporator coil inside your air handler runs below the dewpoint of the return air, condensation forms on the coil, and that water has to be drained out of the home. In a dry climate, the daily condensate volume is small. In coastal South Carolina, where humidity routinely sits high through the cooling season, the volume is meaningful enough that any disruption to the drainage path shows up quickly on the floor.
The drainage path goes through four points: the drain pan beneath the coil, the condensate line out of the pan, an optional condensate pump (in basements or homes where gravity drainage isn't possible), and the exit point at the side of the house. If any of those four points fails, the water has nowhere to go.
Coastal Carolina Comfort flushes the condensate drainage path as part of every spring tune-up for exactly this reason. The Lowcountry-specific factor is not that the AC produces water — it does that everywhere — but that the volume gives a much shorter window between "drainage problem starts" and "water on the floor."
The 5 most common causes of AC water leaks
1. Clogged condensate drain line
The single most common cause Coastal Carolina Comfort sees in Lowcountry homes. The condensate drain line — a white PVC pipe carrying water away from the air handler — slowly fills with algae growth. Warm, dark, wet conditions are exactly what algae need to thrive. Over a season, the buildup constricts the line; eventually it blocks completely, and the drain pan overflows.
The fix: a wet/dry vacuum applied at the outdoor end of the drain line will usually clear the clog in under five minutes. Distilled white vinegar poured down the indoor drain access (often a T-fitting near the air handler) clears the line chemically. Coastal Carolina Comfort techs use a combination on a service visit — vacuum first, then flush — to get the line cleaner than either method alone.
If your home is on a septic system, use white vinegar rather than bleach. Bleach in the drain line can disrupt septic biology when it eventually reaches the system.
2. Cracked or rusted drain pan
The drain pan sits directly under the evaporator coil and catches condensate before it enters the drain line. Pans are usually galvanized steel or plastic. Over years of constant exposure to water, steel pans rust through from underneath; plastic pans crack at stress points from temperature cycling. Either failure produces a leak that bypasses the drain line entirely — the water never reaches the line because it's escaping the pan first.
A drain pan inspection is part of every Coastal Carolina Comfort tune-up. When pans are replaced, the new one is positioned and sealed so condensate flows reliably toward the drain line.
3. Frozen evaporator coil thawing
If the evaporator coil froze recently — from a clogged filter, low refrigerant, or restricted airflow — the meltwater volume can overwhelm the drainage system as the coil thaws. A coil with significant ice buildup produces more water during thaw than the drain line is designed to handle in a short window. The result: water spilling out around the air handler.
If you're seeing meltwater from a recent freeze, the immediate issue is the leak. The underlying issue is whatever caused the freeze. See the related guide on frozen evaporator coils for the diagnostic on the underlying cause.
4. Disconnected or damaged drain line
The drain line connects to the drain pan through a fitting that can loosen over time, especially after vibration from a heavy blower motor or a service event that disturbed the line. A disconnected drain line dumps water directly under the air handler instead of routing it outside. A damaged drain line (cracked from impact or from freeze-thaw cycles in attic installations) leaks at the damage point.
Visual inspection of the drain line from the pan exit to the wall penetration is fast — Coastal Carolina Comfort techs run it on every diagnostic.
5. Condensate pump failure
Homes where the air handler is below the level of the exit point (basement installations, some attic installations with limited slope) use a condensate pump to lift the water from the drain pan to the exterior wall. The pump runs on a float switch — when the reservoir fills, the pump kicks on, water gets pushed out, the reservoir empties, repeat.
Pumps fail in three modes: the motor burns out, the float switch sticks, or the discharge tube clogs. Any of the three produces the same symptom — water pooling around the air handler instead of leaving the home. A failed pump is a single-visit replacement.
When an AC water leak becomes an emergency
Most AC water leaks are inconvenient, not catastrophic. The standard scenario — water seeping around the base of an air handler in a garage, utility room, or attic — gives you time to shut the system off, place towels, and schedule a service visit during regular hours.
It becomes an emergency in three scenarios:
- The water is coming through a ceiling. An attic air handler with a failed drainage path puts water into the drywall below. Ceiling stains, sagging drywall, or active dripping from a ceiling fixture means the leak has been going long enough to soak the drywall — same-day service is the right call.
- Standing water has reached an electrical component. The air handler's blower motor and control board sit close to the drain pan. Water on either is a fire and shock risk. Kill power at the air handler's disconnect switch immediately and call.
- The leak is producing mold-friendly conditions. Standing water plus warm Lowcountry temperatures plus a few days plus drywall or carpet equals mold growth. If the leak has been going more than 24 hours, the response should include a moisture inspection beyond just the drainage repair.
How to prevent AC water leaks in the Lowcountry
Three habits keep most Lowcountry AC drainage failures from happening in the first place:
- Annual condensate drain line flush. Vacuum the outside end, vinegar-flush the inside access. Done once a year in spring, before peak cooling, this prevents the algae buildup that causes the majority of clogs. Coastal Carolina Comfort includes this in the spring tune-up.
- Filter changes on a Lowcountry schedule. Clean filters keep the coil clean, which prevents the freeze-thaw scenario that overwhelms the drain line. Lowcountry pollen seasons (heavy from late February through May, secondary peak in fall) tighten the interval — every 60 days for most homes, more often during pollen weeks.
- Annual drain pan inspection. Galvanized pans last for years before rust breakthrough; plastic pans hold up longer but crack at stress points. A visual inspection during the spring tune-up catches early failures before they leak.
Past these causes? Tell us what's happening.
Same-day Lowcountry routing when an AC is leaking water inside the house.
Call (843) 708-8735 and tell the dispatcher: where the water is appearing (under the air handler, through a ceiling, around the outdoor unit), how long the system has been running, and when the last drain line flush happened. The tech arrives with the parts that match what you've described — drain line cleaning tools, a replacement pan, a condensate pump, or a thermostat — so most water-leak repairs finish in one visit.
What an AC water-leak repair involves
Coastal Carolina Comfort scopes a water-leak repair by which of the five causes is responsible. The scope ranges widely.
Drain line clearing
The lightest-scope repair. Wet/dry vacuum, vinegar flush, occasionally a manual snake for stubborn clogs. Usually under an hour on-site and often rolled into a tune-up visit.
Drain pan replacement
Larger scope. The coil access has to come open, the old pan removed, the new pan positioned and sealed, and the drain line reconnected. Pans are generic in size for most platforms; brand-specific in shape for some.
Frozen-coil thaw plus underlying cause
The water leak is downstream of a frozen coil that needs separate diagnosis. The leak repair is incidental; the real repair is the freeze cause (filter, refrigerant, blower, coil cleaning, thermostat configuration). See the related guide.
Drain line repair or replacement
Disconnected or damaged drain line scope depends on where the damage is. A section replacement at an accessible joint is fast; a full drain-line replacement through a wall cavity is meaningfully larger work.
Condensate pump replacement
Single-visit repair for most pump failures. Brand-matched pump is stocked on the truck for the most common platforms.
Kill power at the air handler's disconnect switch and the breaker before any further inspection. Wet electrical components combine fire and shock risk. The cost of a service call is meaningfully lower than the cost of an electrical or thermal incident from a powered, soaked component.
Get this fixed in your area
Coastal Carolina Comfort runs same-day water-leak response across Summerville, Charleston, and the surrounding Lowcountry. Drainage repairs are among the fastest single-visit AC repairs once the cause is identified. Pick the hub closest to you.
Summerville and Berkeley County
Water-leak repair across Nexton, Cane Bay, Carnes Crossroads, Knightsville, Wescott Plantation, Historic Downtown, and Summers Corner.
Summerville AC repair →Charleston and the Lowcountry
Mount Pleasant, Daniel Island, James Island, West Ashley, Johns Island, North Charleston, and the surrounding Lowcountry communities.
Charleston AC repair →Related diagnostic guides
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AC frozen evaporator coil
The diagnostic for the underlying cause when meltwater from a frozen coil is overwhelming the drainage system.
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AC won't turn on
When the condensate float switch has triggered a safety shutdown to prevent the leak from getting worse.
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AC not cooling
The walk-through when the system runs but isn't keeping the house cool — often a precursor to a freeze and downstream leak.
Frequently asked questions
Why is my AC leaking water inside but the system still runs?
The most common reason: a clogged condensate drain line. The system is cooling correctly — refrigerant pressures are fine, the coil is removing moisture from the air — but the water has nowhere to go because the drain line is blocked. The drain pan fills, overflows, and water ends up on the floor. Coastal Carolina Comfort resolves this in a single visit with a vacuum and a chemical flush.
Is it safe to keep the AC running while it's leaking?
Not for long. Continued running while leaking risks three things: water damage to flooring, drywall, or ceilings; an eventual short or fire if water reaches the blower motor or control board; and mold growth from sustained dampness. Shut the system off at the thermostat, place towels to contain the water, and schedule a service visit. If the indoor temperature is climbing into uncomfortable range, Coastal Carolina Comfort can route same-day.
Can I unclog the condensate drain line myself?
Often yes. A wet/dry vacuum applied at the outdoor end of the drain line (the white PVC pipe exiting the side of the house) will pull most clogs through in a few minutes. Distilled white vinegar poured into the indoor drain access (a T-fitting near the air handler) clears algae chemically. If the line stays clogged after both attempts, the blockage is deeper than a homeowner method can reach — Coastal Carolina Comfort uses pressurized line-clearing tools that resolve the rest.
Why does my AC keep leaking even after I cleared the drain line?
If the leak returns after a successful drain line clearing, one of the other four causes is responsible: a cracked or rusted drain pan upstream of the line, a disconnected drain line at the pan fitting, a failed condensate pump (in homes that use one), or a frozen evaporator coil thawing. Each is a distinct repair; the diagnostic above walks through them in order.
How much condensate water should an AC produce in a Lowcountry summer?
More than systems in dry climates produce. The exact daily volume depends on the home's square footage, the system's tonnage, how often it runs, and the outdoor dewpoint — but in coastal South Carolina the volume is high enough that any drainage failure produces visible water on the floor within hours, not days. That's the difference between Lowcountry homes and inland homes. The drainage system has a shorter margin for error.
Should I be worried about mold from an AC leak?
If the leak was caught within a day and the affected area dries quickly, mold risk is low. If standing water sat for multiple days, especially on carpet, drywall, or behind cabinets, mold can take hold in coastal SC's warm humidity. Coastal Carolina Comfort recommends a moisture inspection beyond the drainage repair when the leak has been ongoing for more than 24 hours.
Water in the wrong place under your AC?
Call (843) 708-8735 for same-day Summerville and Charleston service.
