AC Leaking Water Inside the House: Stop the Damage, Then Fix the Cause

Right now, in this order

• Turn the system off at the thermostat. The coil stops making water within a few minutes. This is the fastest way to stop the leak.
• Put a container and towels under it, and move anything that matters — especially anything electrical below an air handler in a closet.
• If water is coming through a ceiling, do not ignore the bulge. A drywall ceiling holding water will fail suddenly. Puncturing a low point deliberately, into a bucket, is usually less damage than waiting.
• Then call. A condensate leak is not a next-week problem in Florida, because what follows water in a wall cavity here is mold.

Why it escalates so fast here

A system in South Florida summer removes a large volume of water from the air every day, and all of it is meant to leave through one small PVC pipe. When that pipe stops working there is nowhere for a continuous daily supply to go except into your house. It is not a drip that you can watch for a week — it is a tap that does not turn off while the system runs.

Cause 1: a clogged condensate drain line

By far the most common. The line carries warm, damp, slightly dusty water, and biological slime builds up inside it. Eventually it blocks, the pan overflows, and water finds the ceiling below or the floor beside the unit.

If your system has a working float switch, it should shut the cooling off before this happens — that is what that mysterious “AC stopped for no reason” call usually is. The full walkthrough, including safe clearing, is in AC drain line clogs.

Cause 2: a rusted or cracked drain pan

Older air handlers have metal primary pans that corrode from years of standing water. Once a pan is holed, the water bypasses the drain entirely and there is nothing to clear. Replacement is the only real fix, and on an older system it is a data point in the repair-or-replace conversation.

Cause 3: a frozen coil, thawing

When an evaporator coil ices over and then melts, it releases far more water at once than the pan and drain were designed to handle, and it overflows even with a clear line. The tell is a leak that appears after the system has been off for a while, or intermittently rather than continuously.

The freezing itself is the real fault — usually low refrigerant or restricted airflow. See why your AC freezes up.

Cause 4: a disconnected, sloped-wrong or unprimed drain

Installation faults that show up years later. A drain line needs continuous fall to work, and a section that has sagged over a long attic run will hold water and eventually block. A trap that has dried out can also let air pull back through the line, which produces gurgling and poor drainage — and sometimes a sewage smell.

Cause 5: it is not condensate at all

Two impostors worth ruling out. First, duct sweating: uninsulated or poorly insulated ducts in a hot, humid attic condense on the outside and drip, which looks exactly like a leak but is not coming from the unit. Second, an actual roof or plumbing leak that happens to stain near the air handler. If the water appears when the AC is off, it is not condensate.

Working out which one it is

Three quick observations point at the cause without any tools:

• Is the outdoor drain termination dripping while the system runs? A dry stub in the middle of summer means the line is blocked, and the clog is your answer — the safe DIY clearing steps are set out in the drain line article.
• Does the water appear only after the system has been off a while, or only intermittently? That pattern points at a coil freezing and thawing rather than a blockage.
• Does the water appear when the AC is not running at all? Then it is not condensate. Look at the roof, the plumbing, or a duct sweating in a hot attic.

One thing to never do, whatever the cause: bypass or tape up the float switch to get cooling back. That switch is the only thing standing between a clogged pipe and your ceiling.

Preventing the repeat

Condensate maintenance is genuinely the highest-value routine task on a South Florida air conditioner. A yearly tune-up that flushes the line, cleans the pan, verifies the trap and tests the float switch removes most of this category. Where an air handler sits above finished space, a working secondary pan with its own float switch is worth having, because it is the difference between an inconvenience and a ceiling.