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You go to swap the filter, or reach for something in the closet where the air handler lives, and there it is — a puddle. Water pooled under the indoor unit, a damp ring on the ceiling below it, or a slow drip you can only hear when the house is quiet. The first thought is always some version of the same question: is that supposed to happen?
No. It isn't. A little condensation sweating off the cold copper lines is normal. Standing water, an active drip, or a spreading stain is not. An AC leaking water is one of the most common summer calls we run in central Alabama, and the good news is that the usual cause is cheap and often something you can clear yourself. The bad news is that ignoring it is how a $15 fix becomes drywall and mold. So let's walk through why it happens, in the order we'd check it.
First, where the water even comes from
Your air conditioner doesn't just cool the air, it dries it — and in an Alabama July that second job is doing overtime. Warm, humid house air blows across a cold evaporator coil, moisture condenses out of it, and that water drips into a pan and runs out a drain line. On a muggy day a healthy system can pull several gallons out of your house. All of that water is supposed to go quietly down the drain. When you see it on the floor instead, something in that path has failed.
The number-one cause: a clogged condensate drain
If we had to bet before pulling into your driveway, we'd bet on this. The condensate drain line is a narrow PVC pipe, and it stays damp and dark — a perfect place for algae and slime to grow. Over a season it builds up, the line clogs, and the water backs up into the pan until it overflows the edge.
Here's the part worth knowing: many systems have a safety float switch that shuts the cooling off when the pan fills, to stop exactly this. So a clogged drain sometimes shows up not as a puddle but as an AC that quit cooling for no obvious reason — which overlaps with the causes in our guide on why an AC blows warm air. Either way, the fix is the same: clear the line.
The homeowner version: find the drain line (a white PVC pipe near the indoor unit, often ending outside near the foundation). A wet/dry shop vac held to the outdoor end can pull the clog right out — seal around it with a rag and run it for a minute. Some units also have a capped access tee near the air handler where you can pour a cup of distilled vinegar to keep algae down. Do that a couple times a summer and you'll prevent most of these calls.
A frozen coil that's now melting
If you find water and you saw ice earlier — or the airflow had gone weak — the leak may just be a frozen evaporator coil thawing out. A coil freezes into a block of ice, then when the system cuts off it melts faster than the pan can handle and spills over. The water is the symptom; the ice is the actual problem, usually a dirty filter or low refrigerant starving the coil. We break the whole thing down in our post on why an AC freezes up and how to thaw it safely. If you see ice, start there before you mop.
A cracked or rusted-through drain pan
Under the coil sits a pan that catches the condensation. On an older system that pan can rust through or crack, and then water drips straight past the drain no matter how clear the line is. There's usually a secondary pan under the whole unit as a backup, but if that one's compromised too, the water goes to your floor or ceiling. A cracked pan isn't a DIY patch job — it needs the right replacement part for your unit.
A disconnected or poorly sloped drain line
Sometimes the line came loose at a joint, or it was never pitched correctly to begin with, so water sits and eventually finds its way out the seam. This is common on systems installed in a hurry. It's a straightforward fix, but it does mean getting to the connection and re-sealing or re-sloping it properly.
Low refrigerant (the sneaky one)
Low refrigerant drops the coil temperature below freezing, you get ice, the ice melts, and you get water — same chain as the frozen-coil case above. The tell is a leak that keeps coming back after you've cleared the drain and it's still icing up. Refrigerant doesn't get used up in a sealed system, so low charge means a leak somewhere, and that needs a tech with gauges. A spring AC tune-up catches most of these before they strand you in July.
Quick diagnosis table
| What you're seeing | Most likely cause |
|---|---|
| Puddle under the indoor unit, no ice | Clogged condensate drain — clear the line |
| Water plus ice you saw earlier | Frozen coil thawing — check filter, look for the freeze cause |
| Cooling quit for no clear reason | Safety float switch tripped by a full pan — clogged drain |
| Cleared the drain, still leaking | Cracked pan or disconnected line |
| Leak keeps returning, coil keeps icing | Low refrigerant from a leak — needs a tech |
Turn the system off if the water is active. A leak near the air handler can reach the blower motor and the control board — the expensive electrical parts — and water sitting against drywall or a ceiling grows mold faster than you'd think in our humidity. Shut cooling off at the thermostat, soak up what's there, and deal with the source before you run it again.
How to keep it from happening
Most water leaks trace back to a drain line nobody thought about until it flooded. Change your filter monthly through the summer so the coil never freezes, flush the drain line with vinegar a couple of times a season, and get the system a real maintenance visit each year that includes clearing the drain and checking the pan. Boring, cheap, and it's the difference between a dry closet and a ceiling repair.
AC leaking water in Birmingham, Trussville, Vestavia Hills, or Hoover? Schedule a visit with Ethridge HVAC or call (205) 509-4545. We'll find where the water's really coming from — drain, pan, or refrigerant — clear it, and make sure it isn't quietly working on your drywall. Serving central Alabama, one Southern summer at a time.