Diagnosis
The exhaust hose isn't venting hot air properly, or the unit is low on refrigerant. The hose issue is 90% of these calls.
How to Fix It
Check the exhaust hose setup first. Is the window kit installed securely with no gaps? Is the hose fully stretched out, not kinked or crushed? A kinked hose traps heat inside, killing cooling efficiency instantly. Re-seat both ends of the hose.
If That Didn't Work
The unit might be low on refrigerant due to a leak. You'll hear the compressor running but the air won't get cold. This requires a professional repair check.
Heads Up
Never run the unit without the exhaust hose properly installed and venting outside. It will heat your room, not cool it, and can overheat the unit.