While your Hitachi AC is designed to evaporate most of the water that it removes from the air inside your room, excess water does build up inside the unit. The unit should be sloped slightly out the window so any excess drips outside the home. If you notice water dripping into your room, check to see if the unit is angled downward toward the room. If so, adjust it so it is sloped outside the window. Your AC may also drip into your room if the filter is dirty, so you may need to clean or replace the filter to correct the problem.
Imagine forcing a pillow over your face. Hard to breathe right? That's what a dirty filter does to your Hitachi AC blower; the blower has to to work longer and harder to circulate air through the filter.
If the Hitachi AC does not cool, the air filter might be clogged. In such case, air cannot flow through properly which greatly reduces the cooling capacity of the AC. Either clean the air filter or replace it as needed.