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Water dripping from your indoor air conditioning unit onto the floor, or worse, through the ceiling, is never normal. An air conditioner leaking water inside the house signals a drainage failure, a frozen coil, or a cracked pan, and every hour it continues, the water spreads further into drywall, insulation, and flooring. The good news: nearly every indoor AC leak traces back to one of seven causes, and most are diagnosable without special tools.
This guide covers those seven causes, how to tell normal condensation from a real leak, and what to do immediately. If water has spread through ceilings or walls in Lynnwood, WA, our leak detection service maps the full extent. Call ProLine Leak Fix Pros at (425) 380-0028 for availability.
Normal Condensation vs a Real Leak
Air conditioners legitimately produce water. A residential system wrings 5 to 20 gallons of moisture from indoor air on a humid day, and all of it should exit through the condensate drain line to a floor drain or outside. Normal operation means water at the drain exit, nowhere else. Water anywhere else, dripping from the cabinet, pooling under the air handler, staining the ceiling below an attic unit, is a leak, full stop.
7 Causes of an Air Conditioner Leaking Water Inside
1. Clogged condensate drain line
The most common cause by far. Algae and sludge narrow the drain line until water backs up into the pan and overflows. See our full condensate drain guide for clearing methods.
2. Frozen evaporator coil
Low refrigerant, restricted airflow from a dirty filter, or a failing blower lets the coil ice over. When it thaws, the meltwater overwhelms the drain pan and spills everywhere at once.
3. Cracked or rusted drain pan
The primary drain pan under the coil corrodes or cracks with age, especially in older units. Water falls straight through instead of reaching the drain.
4. Disconnected drain line
Vibration, attic work, or a bumped pipe separates the drain line from the pan outlet. Condensate pours directly onto the surrounding surface.
5. Improperly installed or unlevel unit
An air handler that is not level sends condensate to the wrong side of the pan, away from the drain outlet. New installations and recent service are the usual suspects.
6. Dirty air filter choking airflow
A severely clogged filter drops airflow across the coil so far that the coil freezes, linking back to cause 2. This is the easiest cause to fix and the most embarrassing to pay a service call for.
7. Low refrigerant charge
Low refrigerant drops coil temperature below freezing, icing the coil. Unlike a dirty filter, this one needs a professional: refrigerant handling requires certification, and the underlying leak in the refrigerant circuit needs repair.
An AC that ices up and then dumps meltwater is not fixed by just clearing the ice. The ice is a symptom of low refrigerant or starved airflow. Fix the root cause or the cycle repeats, and each flood does more damage than the last.
Frozen Evaporator Coils in Detail
A frozen coil announces itself with weak cooling, ice visible on the refrigerant lines or coil, and sometimes a hissing sound. The immediate response is to turn the cooling off and run just the fan to thaw the coil, which can take several hours. Place towels and a pan to catch meltwater. Once thawed, check the air filter first. If the filter is clean and the coil ices again, you likely have low refrigerant or a blower problem, both professional repairs. Never chip ice off the coil. The aluminum fins and copper tubing damage easily.
| Symptom | Likely cause | First step |
|---|---|---|
| Steady drip from cabinet | Clogged condensate drain | Clear the drain line |
| Weak cooling plus ice on lines | Frozen coil, dirty filter | Replace filter, thaw coil |
| Weak cooling, clean filter, ice returns | Low refrigerant | Call a professional |
| Water under unit, pan dry | Cracked pan or disconnected line | Inspect pan and connections |
| Stain on ceiling below attic unit | Overflow pan breached | Shut system off, inspect pans |
Cracked or Rusted Drain Pans
Primary drain pans live in a harsh environment: constant moisture, temperature swings, and microbial growth. Metal pans rust through, usually at the corners and seams. Plastic pans crack from age and heat. A pan that holds water when you pour a cup into it is fine. A pan that weeps from a seam or corner needs replacement. In attic installations, also verify the auxiliary pan beneath the whole unit is intact and has its own drain or a working float switch.
Diagnosing Your AC Leak
- Check the air filter. If it is clogged, replace it. This resolves a surprising share of cases.
- Look for ice. Inspect the evaporator coil and refrigerant lines for frost or ice buildup.
- Check the pans. Standing water in the primary pan with a dry drain exit means a clog. Water beneath the pan means a crack.
- Trace the drain line. Follow it from the pan to its exit, checking for disconnections, kinks, and blockages.
- Verify the unit is level. A small level on the air handler reveals tilt that misdirects condensate.
What to Do Right Now
Turn the cooling off at the thermostat to stop condensate production, but consider running the fan-only mode to help thaw any ice. Contain the water with towels and buckets, and move valuables away from the drip path. If the ceiling below is bulging or sagging, do not poke it. Place a bucket beneath and call for help. If the leak is active and you cannot find the source, shut the system down entirely until it is diagnosed.
Preventing AC Water Leaks
- Change filters on schedule, monthly in heavy use.
- Flush the condensate line every few months during cooling season.
- Install and test a float switch if your unit lacks one.
- Schedule annual maintenance that includes coil cleaning, pan inspection, and refrigerant checks.
- Keep the area around the air handler clear so leaks are visible early.
- Add a water alarm in the auxiliary pan. See our sensor placement guide.
An air conditioner leaking water inside your home is a drainage or airflow problem, not a mystery. If you have water where it should not be in Lynnwood, North Lynnwood, or nearby, call ProLine Leak Fix Pros at (425) 380-0028. We will find the source and map any hidden moisture before mold gets a foothold.
