AC Leaking Water Inside? 6 Causes and How to Fix It
Water pooling around your indoor AC unit almost always traces back to a clogged condensate drain or a frozen coil. Here are the 6 causes, quick DIY checks, and when to call a pro.
Yuan Pan
Owner & Lead HVAC Technician, Alex Air & Heating · EPA 608 Universal Certified · Ontario, CA
- The #1 cause of an AC leaking water indoors is a clogged condensate drain line backing up into the pan.
- A frozen evaporator coil is the second most common cause - it drips a lot of water when it thaws.
- Turn the system off first: running it while it leaks can cause water damage and, if the coil is frozen, compressor strain.
- Clearing a drain line and swapping a clogged filter are DIY-safe; refrigerant, pan replacement and coil work are pro jobs.
On this page
- Why is my AC leaking water inside the house?
- 1. Clogged condensate drain line (most common)
- 2. Frozen evaporator coil that's now thawing
- 3. Dirty air filter
- 4. Cracked, rusted or overflowing drain pan
- 5. Disconnected or poorly sloped drain line
- 6. Low refrigerant
- What can I fix myself, and when should I call a pro?
Why is my AC leaking water inside the house?
Your AC constantly pulls humidity out of the air; that moisture condenses on the cold evaporator coil, drips into a pan, and drains away through a condensate line. When any part of that path is blocked, backed up, or frozen, the water has nowhere to go but onto your floor. Turn the system off at the thermostat first to stop the leak, then work through the causes below.
1. Clogged condensate drain line (most common)
Algae, dust and slime build up inside the narrow PVC condensate line. Once it clogs, the drain pan overflows. This is the number-one cause. Many systems have a float safety switch that shuts the AC off when the pan fills - if your AC keeps turning itself off with water nearby, this is almost certainly why.
| Cause | Tell-tale sign | DIY or pro? |
|---|---|---|
| Clogged drain line | AC shuts off, water in pan | DIY (clear line) |
| Thawing frozen coil | Ice seen before the leak | Pro (find root cause) |
| Dirty filter | Filter looks gray/clogged | DIY (replace) |
| Cracked/rusted pan | Older unit, rust | Pro |
| Bad drain slope/fitting | Recent install | Pro |
| Low refrigerant | Ice + weak cooling | Pro (EPA-certified) |
2. Frozen evaporator coil that's now thawing
If the coil froze (from a dirty filter or low refrigerant) and then thawed, it releases far more water than the pan and drain can handle at once. If you saw ice on the indoor unit or copper lines before the leak, this is your culprit - fix the underlying freeze, not just the water.
3. Dirty air filter
A clogged filter restricts airflow and can drop the coil below freezing, leading straight back to cause #2. ENERGY STAR recommends checking your filter monthly and changing it at least every three months during heavy-use seasons.
4. Cracked, rusted or overflowing drain pan
On older systems the drain pan can rust through or crack, so water drips past it instead of draining. A pan replacement is a technician job.
5. Disconnected or poorly sloped drain line
If the condensate line was never sloped correctly, or a fitting comes loose, water pools instead of flowing out. Common after a rushed install.
6. Low refrigerant
Low refrigerant lowers coil pressure and temperature, causing freezing and then a thaw-out leak. Refrigerant is never a DIY fix - by law it must be handled by an EPA-certified technician.
What can I fix myself, and when should I call a pro?
DIY-safe: turn the system off, replace a clogged filter, and gently clear a clogged drain line (a wet/dry vac on the outdoor drain outlet often pulls the clog free). Call a pro for: a cracked pan, refrigerant/coil issues, a tripped float switch that keeps recurring, or any leak you can't trace. In the Inland Empire's dusty summers, an annual maintenance visit that clears the drain and cleans the coil prevents most of these leaks.
Frequently asked questions
Turn it off to prevent water damage, but it's usually not dangerous. The exception: if you see ice, don't keep running it - a frozen system can damage the compressor. Clear the obvious causes and call a technician if it continues.
Often yes. With the system off, attach a wet/dry vac to the outdoor end of the condensate line to pull the clog, then flush with a little distilled vinegar. If the pan keeps filling or the AC won't stay on, have a pro inspect it.
Intermittent leaks usually point to a partial drain clog or a coil that freezes and thaws in cycles. Both are worth a maintenance visit before they cause water damage.