Mini split air conditioners (also known as ductless air conditioners) are simple and reliable devices, and most mini split systems will function for many years without ever causing problems. However, they can still suffer from mechanical malfunctions if they aren't properly installed or maintained, and dealing with a mini split that starts dripping water from its indoor evaporator unit can be particularly annoying.
Leaking indoor units can be caused by a variety of underlying problems, and figuring out the cause of the problem yourself can be challenging. The following issues can all cause your mini split's indoor units to start dripping water:
Clogged Condensate Drains
Mini split indoor units function by sucking in warm air from inside your home and cooling it by passing it over pipes filled with chilled refrigerant gases. This process naturally creates a significant amount of liquid condensation inside the unit. Under normal circumstances, this liquid water is channeled away from the unit via built-in condensate drains.
Over time, these condensate drains can become clogged with dust and other solid debris. If these clogs become serious, liquid water can back up into the indoor unit, and start dripping from the unit's vents.
If this problem is causing your indoor unit(s) to drip, unclogging the drains should fix the problem quickly. It is possible to perform this task yourself by unscrewing the drain lines and removing the impacted solid matter., but these thin pipes can be quite fragile, and may be damaged by amateur repairs. Having the drains unblocked by professionals is generally a safer option.
Dirty Air Filters
Your mini split's indoor unit also contains physical filters, which capture and contain any dust and particulate matter that passes through them. These filters must be cleaned or replaced on a regular basis. If they become clogged with debris, air will pass through the unit too slowly.
The longer it takes air to pass through the unit and over the refrigerant pipes, the colder it becomes. If it becomes too cold, ice can start to build up inside the unit. When the split system is deactivated, this ice will melt, overwhelming the condensate drains and causing liquid meltwater to start dripping from the vents.
Fortunately, cleaning and exchanging dirty air filters is a relatively simple task, and the manufacturer's handbook that came with your system will probably contain detailed instructions on how to remove and replace your filters. If you are not comfortable performing this task, call in a professional AC maintenance service to do it for you.
In rare cases, water may start dripping from your system's indoor unit because it was not installed properly in the first place. For example, if the condensate drains are not angled downward at a sufficiently steep angle, they will not drain water away from the unit quickly enough, causing water to flow from the unit's vents during periods of extended use.
In these situations, you should call in an air conditioning repair service to inspect your system, and have any faulty components reinstalled. While this can be an expensive fix, it is still cheaper than purchasing and installing a new unit and will prevent expensive water damage to your home's walls, furniture, and fittings.