An AC produces water as a normal part of its operation: the cold evaporator coil condenses moisture from the room air, and that water drips into the drain tray and exits through the drain pipe. What is not normal is when that water drips inside the room instead of outside. Indoor water leakage is one of the more visible AC problems, and it almost always points to one of five fixable causes.
Quick answer: The most common cause of indoor water leakage is a blocked drain line that prevents condensate from leaving the unit. Water backs up and overflows the drain tray into the room. Other causes are a frozen coil that thaws and overflows the tray, a cracked drain tray, an incorrectly angled installation, or low refrigerant causing ice formation. A blocked drain line is often a DIY fix; the others need a technician.
Cause 1: Blocked Drain Line (Most Common)
The drain line runs from the indoor unit's drain tray to an exit point outside the building. Over time, algae, mould, dust, and debris accumulate inside the pipe and form a blockage. Water can no longer drain away, the tray fills up, and water overflows into the room. You may notice water dripping steadily from the bottom of the indoor unit, or a wet patch on the wall below it.
DIY fix: Attach a wet-dry vacuum to the outdoor end of the drain pipe and suck the blockage out. Alternatively, pour a cup of diluted white vinegar (half water, half vinegar) into the drain tray through the filter opening and let it sit for 30 minutes before running the unit. This dissolves biological buildup and can clear a partial blockage. For a persistent blockage, a technician can clear it with a wet-dry vacuum or a thin flexible brush.
Cause 2: Frozen Evaporator Coil
When the evaporator coil ices up (most commonly from a dirty filter restricting airflow, but also from low refrigerant), the ice can build up to the point where it melts faster than the drain tray can handle. The overflow drips inside the room. You may notice water leakage accompanied by reduced or no cooling and, if you remove the front panel, visible ice on the copper pipes or the coil.
Fix: Switch the AC off and let the ice thaw completely (1 to 3 hours). Clean the filter. If icing recurs after a filter clean, the unit needs a refrigerant check from a technician. For the full freeze-up guide, see why is my AC freezing up.
Cause 3: Cracked or Displaced Drain Tray
The drain tray that collects condensate from the coil is usually a plastic component. Over years of use, it can develop hairline cracks that allow water to drip straight through before reaching the drain outlet. Alternatively, it may shift out of position during maintenance or a unit move, leaving a gap between the tray and the coil. Water misses the tray entirely and drips inside.
Fix: A technician needs to open the unit and inspect the tray. Hairline cracks may be sealable with an appropriate waterproof sealant, but a cracked tray is usually replaced. This is not a home fix because it requires accessing the inside of the unit casing.
Cause 4: Incorrect Installation Angle
The indoor unit must be installed with a very slight tilt toward the drain side, so that gravity pulls condensate toward the drain outlet. If the unit was installed perfectly level, or tilted away from the drain, water pools in the tray and eventually overflows at the lowest point, which may be the front face of the unit, dripping into the room.
Fix: A technician adjusts the mounting bracket to give the unit the correct slight inward tilt toward the drain side. This is a simple adjustment but requires remounting the unit.
Cause 5: Low Refrigerant
Low refrigerant causes the evaporator coil to run at a lower pressure than intended, dropping its temperature below freezing. Ice forms on the coil and, as it melts, produces more water than the drain tray is designed to handle. Low refrigerant also causes noticeably reduced cooling output. This needs a licensed technician to locate the leak, repair it, and recharge the system.
What to Do Immediately
- Place towels or a container below the indoor unit to catch dripping water and protect the floor and walls.
- Switch the AC off. Running it while leaking can worsen the tray overflow and potentially wet electrical components.
- Check the drain line first: pour water into the drain tray and see if it flows out freely.
- Check the filter: if it is heavily clogged, clean it and allow any ice to thaw before running the unit again.
- If neither of these resolves it, call a technician.
Check your AC is correctly sized, which prevents the short-cycling that contributes to drain tray overflow.
AC Tonnage CalculatorKey takeaways
- A blocked drain line is the most common cause of indoor water leakage and is often a DIY fix.
- A frozen coil thawing and overflowing is the second most common cause. Clean the filter and let the unit thaw first.
- Cracked drain tray, incorrect installation angle, and low refrigerant all need a technician.
- Switch the AC off when it is leaking indoors and place towels to protect surfaces while you diagnose.
- Prevent leaks by cleaning filters regularly and flushing the drain line monthly with diluted vinegar.
Frequently Asked Questions
Why is my AC dripping water inside the room?
The most common cause is a blocked drain line. Water backs up in the drain tray until it overflows inside the room. Other causes include a frozen coil, a cracked drain tray, an incorrectly angled installation, or low refrigerant.
Is AC water leakage dangerous?
Water dripping onto walls, flooring, or electrical components can cause damage over time and create conditions for mould growth. Address it promptly. Switch off the unit and place towels before investigating the cause.
Can I fix AC water leakage myself?
A blocked drain line is often a DIY fix using a wet-dry vacuum or a vinegar flush. A dirty or frozen coil can be addressed by cleaning the filter and letting the unit thaw. A cracked tray, incorrect installation, or refrigerant issue needs a technician.
How do I stop my AC from leaking water indoors?
Clean filters regularly to prevent coil icing. Check the drain line monthly for blockages. Ensure the unit tilts slightly toward the drain side. Have an annual professional service including a drain and coil inspection.
Sources and Further Reading
- Bureau of Energy Efficiency, India, AC maintenance standards (beeindia.gov.in)
- ENERGY STAR, air conditioner maintenance and troubleshooting (energystar.gov)
- U.S. Department of Energy, common AC problems and fixes (energy.gov)
General diagnostic guidance for AC water leakage. Refrigerant issues, tray replacement, and installation angle corrections require a licensed HVAC technician.