Finding water on the wall or floor below an indoor AC unit is alarming, but in most cases the cause is more mundane than a major mechanical failure.
A clogged condensate drain line is the most frequent culprit. As a unit cools the air, it also removes moisture, which is meant to flow out through a drain line. Dust, algae, or debris can block that line over time, causing water to back up and overflow instead.
A dirty air filter can also contribute indirectly — restricted airflow across the coil can cause it to freeze, and when that ice later melts faster than the drain can handle, it shows up as a leak.
Less often, a cracked drain pan or a unit that isn't sitting level can cause water to escape from the wrong place entirely. Either way, the fix is usually straightforward once the actual source is identified, which is why a proper inspection matters more than guessing.