The indoor unit drips or leaks water down the wall, sometimes blowing mist. Condensate must all run into the tray and the drain; water spills when the tray or the drain cannot take it away, when the unit is not level, or when the coil ices up and then melts. The table below lists the causes technicians found for this symptom.
A summary of 51 public questions with this symptom that got a fix in technicians' groups (2021–2026). 51 name one main cause, 11 of them confirmed by the poster as the fix.
Causes technicians found, by number of cases
| Cause | Cases | Share | Confirmed |
|---|---|---|---|
| Installation (long or high pipe run, kinked pipe, unit not level) | 18 | 35% | 4 |
| Drain pipe or tray | 13 | 25% | 2 |
| Dirty indoor coil or filter | 13 | 25% | 2 |
| Low refrigerant, leak | 3 | 6% | 2 |
| Blocked pipe, capillary, strainer, moisture | 2 | 4% | 1 |
| Temperature sensor | 1 | 2% | 0 |
| Overcharge, wrong refrigerant | 1 | 2% | 0 |
| Total | 51 | 100% | 11 |
Typical repair cases
Installation (long or high pipe run, kinked pipe, unit not level)
- Mitsubishi Electric: Two newly purchased 2.5 HP Mitsubishi air conditioners have been misting heavily and causing water dripping after 10 days of use at a hair salon. The units were cleaned but still mist. The poster asks what the cause is… – The main cause is that the indoor unit is mounted too close to the ceiling, which reduces return air and heat exchange, causing the indoor unit to condense moisture and mist. It is recommended to lower the unit about 15-30 cm below the ceiling, increase the fan speed, clean the indoor unit, and check that the drain…
- The air conditioner near a canal keeps leaking refrigerant (copper pipe). The indoor unit has been replaced several times across 3 generations of units, and recently there is a smell of leaking gas. The homeowner asks… – In an environment near a black canal containing chemicals and acid, choose a domestic brand unit with an aluminum coil or a coil with anti-corrosion coating, and copper pipe of greater thickness. During installation, the water trap and drain pipe must be built correctly to technical standards, and the indoor unit coil…
Drain pipe or tray
- Aqua: The Aqua air conditioner is splashing water out of the fan after the technician removed, cleaned and reinstalled it, and the customer reports that water is still leaking. – Water splashing out of the fan is usually caused by the indoor unit being installed misaligned, or by the rear drain pan being clogged with dirt after cleaning. Lift the unit to inspect it, and rinse thoroughly to remove the cloth fragments and dust on the unit and drain pan, using a low-pressure nozzle to avoid…
- LG: A newly installed LG air conditioner, used for 3 months, is leaking water. The homeowner asked for a diagnosis of the cause. – Water leakage is usually caused by a dirty indoor unit, a blocked drain pipe, or incorrect installation height without a proper slope. Clean the indoor unit, clear the drain pipe, adjust the installation height, and create the proper slope; if the room is not sealed or has a hot window, install shielding to reduce…
Dirty indoor coil or filter
- Samsung: Samsung air conditioner is leaking water: water does not drip into the drain pan but falls directly into the shell and splashes out, even though the pan has been cleaned. – Water dripping straight from the indoor unit is usually caused by a dirty film coating the evaporator, which stops the water from flowing down into the pan, or by a shortage of refrigerant gas. Remove the indoor unit, clean it thoroughly with a dedicated chemical cleaner and a cloth, then check the gas pressure before…
- LG: An LG air conditioner is leaking/overflowing water. The poster is asking for advice on the cause and how to fix it. – Water dripping from the indoor unit is usually caused by condensation on the refrigerant line when the insulation is missing or damaged, especially the section above the indoor unit. Check and re-wrap it with sealed insulating foam, and also check the evacuation and the slope of the drain pipe.
Low refrigerant, leak
- Samsung: The Samsung air conditioner has been thoroughly cleaned, has enough refrigerant, and the fan operates normally, but it still shows an error. The poster asks for a way to fix it. – The most likely cause is a refrigerant shortage causing the indoor unit to drip water. Check the refrigerant pressure and recharge to the correct pressure (approximately 160 psi) following the proper procedure. At the same time, thoroughly clean the indoor unit and inspect the drain hose to rule out secondary causes. (confirmed by the poster)
- The air conditioner runs at a low temperature (below 26 degrees), causing the indoor unit coil to become covered in condensation. The water does not drain into the drain pan, so the airflow passing through creates a… – When the air conditioner runs too deep, water condenses heavily, the coil is flooded with water and it makes a gurgling noise, which is a sign of low refrigerant (gas) or a coil with condensate buildup. Check the refrigerant pressure, inspect and top up the correct amount if it is low, and also remove the indoor unit… (confirmed by the poster)
Blocked pipe, capillary, strainer, moisture
- Toshiba: The Toshiba air conditioner's condensate drain pipe is blocked at the drain pan outlet. I tried drying and hot water, but it is still not clear and the water still does not drain into the pan. – The blockage is in the drain pipe behind the cabinet, with a constriction caused by dirt. Remove the rear access cover to clear the drain line completely; you can pour hot water directly into the pipe and suction it out several times. Additional drying only melts ice and does not solve the blockage.
- The air conditioner is leaking water, and the poster is asking how to fix it because they have not yet been able to reach a technician. – Water leakage from an air conditioner is usually caused by a blocked drain line due to accumulated dust and dirt. To check, pull out the drain pipe: if water flows, the drain path is clear. If no water flows, clear the pipe by blowing or suctioning the drain hose, or call a technician to clean it thoroughly. (confirmed by the poster)
Temperature sensor
- The air conditioner is set to 26 degrees and after running for about 3 hours it leaks water and freezes over, with water blowing out with the wind; a technician has been called but has not yet fixed the problem. – Freezing and water leakage are usually caused by a faulty evaporator temperature sensor that does not cut out the outdoor unit, or by a very dirty indoor unit, low refrigerant (gas), or incorrect installation without proper drainage slope. Check the sensor, clean the indoor unit (remove and spray the coil inside),…
Overall
- Mostly installation (indoor unit tilted away from the drain outlet, drain pipe running uphill, sagging, its end under water) and a dirty coil or tray – check these before thinking of the refrigerant.
- A blocked or kinked drain: clear it and pour water into the tray to see that it all runs away.
- Leaking together with an iced coil: check the charge and the coil's cleanliness – the melting ice is more than the tray holds.
Note: this is technicians' field experience, not a manufacturer's document.
Safety: switch off both the indoor and the outdoor unit before opening a cover or touching a board; the capacitors on the outdoor board stay charged for a while after power-off - wait for the board's lamps to go out and measure before touching. Refrigerant and high-voltage work belongs to a certified technician.