Is your Hitachi ac broken? Chances are, it's not.
Your Hitachi AC is not some sort of miracle machine. It's a normal machine. Normal machines have normal parts that need normal maintenance and replacement.
Don't fret. The most important thing you can do to keep your Hitachi AC functioning properly is really, really simple. Just change the filter.
Dryers have lint traps to catch all the, well, lint, that falls off your clothes. Hitachi AC have filters to catch all the dirt particles in the air. Just like you have to clean the lint off the lint trap to keep air flowing through your dryer, you have to clean the dirt off your AC filter (or replace it) to keep the air flowing through your AC.
If this sounds like a chore you can skip, think again. Dirty filters kill your unit's efficiency
Once you have your filter out, you have a choice to make. Some filters are washable. Just wipe them down with a damp rag and pop them back in. Others must be replaced.