AC Leaking Water Inside: Common Causes and What to Do

An AC leaking water inside usually has a drainage problem: a clogged condensate drain line, a failed condensate pump or a cracked drain pan. A frozen indoor coil that melts can also flood the area. Turn the system off at the thermostat, keep water away from anything electrical, and then work through the checks below.

Your air conditioner pulls moisture out of the air as it cools, and on a humid day that can be gallons of water. Normally it drips into a pan and drains away through a pipe. When any part of that path fails, the water ends up on your floor or ceiling instead. This guide covers what to do first, the likely causes, what you can safely check, and what repairs typically cost.

What should you do first if your AC is leaking water?

Safety comes before finding the cause. Water and electricity are a dangerous mix, and an indoor unit sits near outlets, wiring and often a furnace.

1. Turn the system off at the thermostat. This stops more water from forming. Carrier says not to keep running the AC while it's leaking (Carrier).
2. Keep water away from outlets, cords and the unit's wiring. Move extension cords, power strips and anything plugged in out of the wet area if you can do it without standing in water.
3. If water has reached wiring, an outlet or the electrical panel, or you see sparks, stay clear and call 911. Don't step into standing water near anything electrical, and don't touch the unit.
4. Turn off the AC's breaker only if you can reach the panel while standing on dry ground. Flip the breaker, but don't open the panel's cover.
5. If water is coming through a ceiling, stay out from under it. A ceiling that's bulging or sagging can give way. Put a bucket down and keep people and pets out of the room.
6. Contain the water. Use towels, a mop or a wet-dry vacuum on the floor once the area is safe. Move rugs, boxes and furniture out of the way.
7. Take photos. Pictures of the water, the unit and any damage are useful for your records and for the company you call.

Once the system is off and the area is safe, you can look for the cause.

Why is my AC leaking water inside?

These are the common causes, in rough order of how often they happen.

1. A clogged condensate drain line

This is the most common cause. The drain line is a small pipe, usually white PVC, that carries water from the drain pan to the outside or to a floor drain. Over time, dust, algae and mold can grow inside and block it.

Carrier lists the clogged drain line first, and says a blockage can cause water to back up and overflow into your home (Carrier). Trane also says the drain line can clog from lack of maintenance (Trane).

Signs it's the drain line:

• Water around the base of the indoor unit, often after hours of running.
• The drain pan under the coil is full.
• No water dripping from the end of the drain line outside on a humid day when the AC has been running.
• A musty smell near the unit.

Some systems have a safety switch that shuts the AC off when the pan fills. If your AC stopped cooling and there's water in the pan, a clogged line may have tripped it.

2. A frozen evaporator coil

When the indoor coil freezes, it builds up ice. When the system shuts off, or the ice gets thick enough to block airflow, that ice melts faster than the pan and drain can handle, and water spills over.

Carrier links a frozen coil mainly to restricted airflow from a dirty filter, and also to low refrigerant (Carrier). Signs include:

• Ice or frost on the copper lines near the indoor or outdoor unit.
• Weak airflow from the vents.
• Air that isn't as cold as usual. See our guide on an AC blowing warm air for more on this.
• A leak that shows up after the AC turns off.

3. A failed or unplugged condensate pump

If your indoor unit is in a basement or another spot where water can't drain downhill, a small condensate pump lifts it out. It usually sits on the floor next to the unit and has a plastic tank and a tube running up and out.

Trane lists a condensate pump that has come unplugged as a reason the drain pan overflows (Trane). Pumps can also fail from age, a stuck float or a blocked outlet tube.

Signs it's the pump:

• Water pooling near the pump.
• The pump's tank is full, but the pump isn't running.
• The pump is unplugged, or the outlet it's plugged into has no power.

4. A cracked or rusted drain pan

The drain pan sits under the indoor coil and catches the water. Older metal pans can rust through, and plastic pans can crack. Carrier says the risk rises with the system's age and with humidity (Carrier).

Signs it's the pan:

• Water under the unit even though the drain line is clear.
• Visible rust, cracks or holes in the pan.
• A slow, steady drip rather than a sudden overflow.

5. A dirty air filter

A clogged filter doesn't leak water by itself, but it's a common reason the coil freezes, which then leaks as it thaws. Carrier recommends checking the filter monthly and replacing it every one to three months (Carrier).

6. Low refrigerant from a leak

Low refrigerant can make the indoor coil too cold, so it freezes and later leaks water as it melts. An AC doesn't use up refrigerant, so if it's low, there's a leak. Carrier treats a suspected refrigerant leak as urgent (Carrier). This one is always a job for a pro.

7. A drain line that's loose, damaged or poorly sloped

The drain line needs to slope downhill all the way so water flows out. Carrier suggests confirming it slopes continuously downward (Carrier). A line that has sagged, come apart at a joint or been knocked loose can leak at the joint or let water sit and back up. Trane also says to look for kinks in the line (Trane).

What if the water is on the ceiling?

If your air handler is in the attic or above a ceiling, a leak often shows up as a stain, drip or bulge on the ceiling below. Many attic units sit over a second, larger pan that catches overflow. If that pan fills or has its own clogged drain, the water comes through the ceiling.

Ceiling leaks can cause damage that isn't easy to see, such as wet insulation or drywall. Stay out from under a sagging ceiling, don't climb into the attic to look around wet electrical wiring, and tell the company where the water is when you call.

What can you safely check yourself?

With the system off and the area dry and safe, these checks are fine for most homeowners. They don't involve opening the unit's electrical panels.

1. Check the air filter. If it's gray, matted or caked with dust, replace it with one the same size.
2. Look for ice. Check the copper lines near the indoor unit. If you see ice, leave the system off so it can thaw, with towels down to catch the water. Don't chip at it.
3. Check the condensate pump. Make sure it's plugged in and the outlet has power. Trane suggests checking that the pump is plugged in as a first step (Trane). If it's plugged in and the tank is full but it isn't running, leave it for a pro. Keep cords out of any standing water.
4. Find the outdoor end of the drain line. It's often a short white pipe near the outdoor unit or the foundation. On a humid day after the AC has run, it should drip. If it's dry, the line is likely blocked.
5. Clear the drain line, if you're confident which line it is. Carrier suggests turning off the AC and using a wet-dry vacuum at the outdoor end of the drain line to pull out the clog (Carrier). Carrier also says that if you're not sure which line is the condensate drain, don't do this, and call an HVAC professional instead.
6. Look at the drain pan. If you can see it without removing panels, check for cracks, rust or standing water. Don't remove screws or covers to get to it.

What you shouldn't do

• Don't run the AC while it's leaking. It will keep making water.
• Don't open the unit's electrical panels or your main electrical panel.
• Don't stand in water near anything electrical.
• Don't add refrigerant or try to thaw ice with heat. A hair dryer or heat gun near wiring and water is a hazard.
• Don't climb into an attic over a wet ceiling. Wet drywall can give way, and attic wiring may be wet.

When should you call a pro?

Call an HVAC company if:

• Water has reached wiring, an outlet or the furnace.
• The leak is coming through a ceiling.
• You cleared the drain line, but the leak came back.
• The condensate pump is plugged in but isn't working.
• You see ice on the coil or lines, or it refreezes after thawing.
• The drain pan is cracked or rusted.
• You suspect low refrigerant.
• You can't find where the water is coming from.

Carrier says a leak becomes urgent if it's damaging the home's structure or if a refrigerant leak is suspected (Carrier). If water has damaged floors, walls or ceilings, you may also need help drying the area to prevent mold.

What will the pro check?

A technician will usually trace the water from the coil to the drain:

• The drain pan. Whether it's full, cracked or rusted, and whether water is sitting in it.
• The drain line. Whether it's clogged, kinked, disconnected or poorly sloped, and clearing it if needed.
• The overflow safety switch. Whether the system has one and whether it's working.
• The condensate pump. Its power, float and outlet tube.
• The coil. Whether it's frozen or dirty, and why.
• Airflow. The filter, the blower and the vents.
• Refrigerant. Pressure readings if the coil has frozen, to check for a leak.
• Secondary pan. For attic units, whether the overflow pan and its drain are clear.

How much does it cost to fix an AC leaking water?

Most visits start with a service call or diagnostic fee. Many contractors charge $75 to $250 for the diagnosis (Fixr), and it's often credited toward the repair if you hire them. Our guide to HVAC service call fees explains what to ask.

Published national ranges, as of 2026:

• Clearing a clogged condensate drain line: usually $75 to $250 (Fixr).
• Condensate pump replacement: $100 to $500 (Fixr).
• Drain pan replacement: $200 to $600 (Fixr).
• Refrigerant leak repair and refill: $200 to $1,500 (Fixr).
• Evaporator coil replacement: $400 to $2,700 (Fixr).

Carrier puts the typical cost to fix an AC leak at $200 to $1,500, depending on severity and location (Carrier). The most common cause, a clogged drain line, is also one of the cheapest to fix.

These ranges cover the AC repair only. Drying out or repairing water-damaged floors, drywall or ceilings is a separate cost.

Should you repair or replace the AC?

A leak alone is rarely a reason to replace a system. Drain lines, pumps and pans are all replaceable parts. It's worth pricing a replacement when:

• The system is older. ENERGY STAR suggests considering replacement when an air conditioner is more than 10 years old (ENERGY STAR).
• The coil or refrigerant is the problem. A leaking coil on an older system is a bigger repair, and that's often when people compare it with a new unit.
• It keeps needing repairs. ENERGY STAR points to frequent repairs and rising bills as signs it may be time (ENERGY STAR).

For comparison, most homeowners pay between $5,000 and $12,000 to replace a central AC (Fixr).

Questions to ask the HVAC company

• Where exactly is the water coming from, and how did you confirm it?
• Was the coil frozen, and if so, why?
• Does my system have an overflow safety switch, and is it working?
• What's your service call fee, and does it go toward the repair?
• Can I get the price in writing before you start?
• What can I do to keep the drain line clear?
• Is your work guaranteed, and for how long?
• Are you licensed and insured where I live?

How to help prevent AC leaks

• Change the filter regularly. Carrier recommends checking it monthly and replacing it every one to three months (Carrier).
• Have the drain line checked every year. Carrier suggests inspecting it at least once a year, ideally before cooling season (Carrier).
• Have the drain pan inspected. Carrier also recommends checking the pan for rust or cracks at least once a year (Carrier).
• Keep the condensate pump plugged in. Make sure no one unplugs it to use the outlet.
• Get a yearly tune-up. A pro can clean the coil and drain and spot problems early.

The bottom line

An AC leaking water inside most often has a clogged drain line, a failed condensate pump, a cracked drain pan or a frozen coil. Turn the system off, keep water away from anything electrical, and call 911 if water has reached wiring or you see sparks. Then check the filter, the pump and the drain line, and call a pro if the leak continues.

Other guides that may help: an outdoor unit that hums but won't start.

If you'd like to understand the likely cause and typical costs before you call anyone, Bellwick can walk you through a few short questions and help you prepare for the conversation with a local company. Check my heating & AC