AC Leaking Water Inside the House: What to Do First

Water where it should not be gets a different kind of attention than warm air. A puddle under the indoor unit, a stain spreading across a ceiling, a drip from a closet: these damage the house while you decide what to do. So this guide is organized as the first hour, in order, rather than as a list of causes. The causes come at the end, once the house is protected.

Minute one: power and water do not mix

Look at where the water is. If it is touching, or dripping toward, the furnace or air handler, an electrical outlet, a junction box or any wiring, switch the AC breaker off at the panel before you do anything else. Then set the thermostat to Off. If the water is only in the drain pan area and nowhere near electrical parts, the thermostat alone is enough for now, but switch cooling off either way: every hour the system runs adds water.

Do not stand in water to reach the breaker. If the panel itself is wet or the water is near it, call and describe the situation rather than touching it.

The next ten minutes: contain and record

Put towels, a tray or a bucket under the drip. Move anything stored nearby, especially cardboard and electronics. If the leak is from a ceiling, put a container under it and, if the drywall is bulging, do not poke it; a sagging ceiling holding water is heavier than it looks.

Then take photographs of everything: the puddle, the stain, the drip point, the indoor unit and the area around it. The technician will want to see where the water started, and if you later need a written description of the cause for an insurer, the pictures help. (Whether a policy covers water damage is between you and the insurer; we cannot advise on that.)

Find the source without opening anything

Water near an indoor unit has four usual sources, and you can often tell which without tools.

• Overflowing drain pan. Standing water in the pan area, or dripping from its edge. The drain line is blocked and the pan has filled.
• Melting ice. Frost or ice on the larger copper line near the unit, or a coil that was recently iced. A thawing coil releases far more water than the pan can drain, and the leak looks dramatic for an hour and then stops. The frozen coil article explains why the ice formed.
• The drain line itself. Water at a joint in the white PVC pipe leaving the unit, or a fitting that has visibly come apart.
• A sweating copper line. Drips along the large insulated pipe where the insulation is missing or wet. This is condensation on the pipe, not a leak from the unit, and it is the least urgent of the four.

While you are there, look outside for the end of the drain line. On a humid day with the system running there should be a slow drip from it; if there is none and the pan is overflowing, the line is blocked. Note it; do not try to clear it with wire or chemicals.

Decide how urgent it is

Call now if water reached wiring or electronics, if a ceiling is sagging, if ice is present (the system must not run until it thaws and the cause is found), or if the leak returned within a day of being mopped up. Book a daytime visit if the water is contained, the system is off, and the source looks like a blocked drain. The AC leaking water guide has the full stop-and-call list and the safe checks in one place.

Either way, the visit happens within 24 hours of the call. The diagnostic visit page describes how it runs, and the pricing page lists the diagnostic visit fee by time of day so you can weigh a night call against a morning one.

Why the water is there

Every hour of cooling pulls moisture out of the air, and on a humid Los Angeles day that adds up to gallons. It collects on the cold indoor coil, drips into a pan beneath it, and runs out through a drain line. The path fails in predictable ways. Algae and dust slowly narrow the drain until it backs up; this is the most common cause and the one that late summer exposes, because long run times produce more water than a half-blocked line can pass. Coils freeze because of a dirty filter or a refrigerant leak and then thaw faster than the pan can cope. Older pans crack or rust through. Where the unit sits below the drain outlet, a small condensate pump lifts the water out, and when the pump or its float fails, its reservoir overflows. Fittings get knocked apart during other work.

Many systems have a float switch in the pan that cuts the AC off when water rises. If your AC stopped working at the same time the leak appeared, that switch did its job; the AC won’t turn on guide mentions it among the reasons a system goes silent.

What the repair usually involves

A blocked line is cleared from the outside end and flushed, and its slope is checked. A frozen coil gets its cause found, which is airflow or refrigerant, not the ice. A cracked pan is replaced. A failed pump is replaced and tested under load. Missing pipe insulation is refitted. None of these is dramatic, and you hear the price before work starts. Ceilings and flooring are a separate trade; the technician will tell you when the leak is fully stopped so that repair is not wasted.