AC Leaking Water

By HVAC Load Calculate Team, licensed HVAC professionals · Updated July 2026

The most likely cause is clogged condensate drain line, or full drain pan from clog. Water dripping, pooling, or leaking from indoor AC unit or ceiling below air handler. Most cases take diy: 45-60 minutes | professional: 1-2 hours | pan replacement: 2-4 hours to resolve once you know which cause you are dealing with, and the checks below start with the ones you can do yourself in a few minutes.

How to Confirm This Is Your Problem

You are probably dealing with this exact issue if you notice one or more of these signs:

Water pooling around indoor air handler
Dripping from ceiling below attic unit
Wet spots on walls near vents
Standing water in drain pan
AC shuts off unexpectedly
Musty smell from vents
Water stains on ceiling
Gurgling sounds from drain line

Step-by-Step Diagnosis

Follow these steps to identify the exact cause of your problem:

Turn off AC to prevent water damage
Locate indoor air handler and check drain pan
Look for standing water in drain pan
Find condensate drain line (usually white PVC pipe)
Check if drain line is clogged (blow into it)
Inspect float switch in drain pan
Verify drain line slopes downward continuously
Check if drain line exits outside properly
Look for ice on evaporator coils
Inspect air filter for severe clogging
Check if problem worsens on humid days
Note if AC has been running continuously

What Causes It, Ranked by Likelihood

1. Clogged condensate drain line

The number one cause by a wide margin. Algae and slime build up in the PVC drain line until water backs up into the pan and overflows. Find the drain outlet outside, and pull the clog with a wet dry vacuum held to the pipe end for 2 minutes. A cup of distilled vinegar down the line twice a season keeps it clear.

One of the most frequent culprits. You can usually fix this yourself, typical cost $10-30 (vinegar/bleach/wet vac).

2. Full drain pan from clog

Once the line clogs, the primary pan under the evaporator coil fills and spills. Attic installations should have a secondary pan with a float switch that kills the AC before water reaches your ceiling. If your ceiling already shows a stain, address it same day; drywall and insulation damage compounds fast.

One of the most frequent culprits. You can usually fix this yourself, typical cost $0-20 (DIY cleaning).

3. Frozen evaporator coils melting

If the coil froze from a dirty filter or low refrigerant, the melt water when the ice thaws can exceed what the pan handles. Puddles that appear right after the AC shuts off point this direction. Fix the freezing cause, not just the water.

Worth checking after the common causes. You can usually fix this yourself, typical cost $15-30 (filter + defrost).

4. Disconnected or damaged drain line

PVC joints that were never glued eventually separate, especially where the line gets bumped in the attic or closet. Trace the line from the pan to the exit and look for drips at every fitting. A $5 coupling and glue fixes it.

Worth checking after the common causes. You can usually fix this yourself, typical cost $20-50 (PVC supplies).

5. Rusted or cracked drain pan

Metal primary pans on systems 15+ years old rust through, and plastic pans crack from age and UV. Water dripping from the middle of the air handler rather than the drain fitting is the tell. Pan replacement requires pulling the coil, so it runs $200 to $600.

Less common, but it happens. This one needs a professional, typical cost $200-500 (pan replacement).

6. Improper drain line installation

Drain lines need a downward slope of at least a quarter inch per foot and a trap near the air handler. Lines run flat or uphill hold standing water that clogs constantly. If you clear clogs more than once a season, the pitch is probably wrong.

Less common, but it happens. This one needs a professional, typical cost $150-400 (reinstallation).

7. Condensate pump failure

Basement and closet installs below the drain level use a small pump. When it fails or its float sticks, the reservoir overflows onto the floor. Test it by pouring a cup of water in; the pump should kick on within seconds. Replacements cost $50 to $150 plus install.

Less common, but it happens. This one needs a professional, typical cost $150-350 (pump replacement).

DIY Solutions

You will need wet/dry vacuum, white vinegar or bleach, towels, bucket, screwdriver, flashlight, drain snake (optional). Plan on 45 minutes to 1 hour.

Turn off AC at thermostat and breaker
Soak up standing water from drain pan with towels
Locate drain line access port (T-fitting with cap)
Pour 1 cup white vinegar into access port
Wait 30 minutes for vinegar to break down algae
Flush with 1 cup of water
Use wet/dry vacuum on outside drain end to suck out clogs
If drain won't clear, use drain snake or stiff wire
Clean drain pan with bleach solution
Reinstall everything and test by pouring water in pan
Turn AC back on and monitor for 24 hours
Pour 1 cup vinegar monthly to prevent future clogs

Before you start, know these safety limits:

Turn off power before working on AC unit
Wear gloves - drain water contains bacteria and mold
Don't mix bleach and vinegar - use one or the other
Be careful on ladder if accessing attic unit

When to Call a Professional

Stop and call a licensed technician if you run into any of these situations:

Drain pan is rusted or cracked
Drain line cannot be cleared after DIY attempts
Water damage to ceiling or walls
Condensate pump not working
Drain line disconnected inside wall
Severe algae or mold growth in unit
Leak from unknown location
Multiple recurring leaks

Find Local HVAC Contractors

How to Keep It From Happening Again

Pour 1 cup vinegar down drain monthly during cooling season
Install drain line trap to prevent clogs
Add algae tablets to drain pan quarterly
Schedule annual drain line flush with maintenance
Install condensate overflow shutoff switch
Insulate drain line in attic to prevent condensation
Replace air filter regularly to prevent coil freezing

Frequently Asked Questions

Is it normal for AC to leak water outside?

Yes, it's completely normal for water to drip from the condensate drain line outside. Your AC removes gallons of moisture from indoor air daily. However, water leaking inside your home is never normal and needs immediate attention.

How much does it cost to fix an AC leak?

DIY drain line cleaning costs $10-30. Professional drain cleaning is $100-250. Drain pan replacement runs $200-500. Major repairs like coil replacement cost $800-2,000. Most leaks are simple clogs you can fix yourself.

Why does my AC leak water only sometimes?

Intermittent leaks often occur during high humidity when your AC removes more moisture, overwhelming a partially clogged drain. The clog may clear temporarily when water pressure builds up, then clog again.