DIAGNOSIS The unit is likely overheating due to restricted airflow. The thermal overload protector is tripping.
FIX Check the air intake and exhaust vents. Ensure the exhaust hose is fully extended and not kinked. Clean the air filter. Ensure there's at least 20 inches of clearance around the unit, especially the back.
IF THAT DIDN'T WORK The condenser coil on the back could be clogged with dust and lint. Vacuum the coil fins gently. A severely dirty coil causes overheating.
HEADS UP Never run this unit with the window kit not properly installed and sealed. Hot air short-cycling back into the room will cause immediate overheating shutdown.