DIAGNOSIS You're seeing an E2 error, which means the unit's temperature sensor inside the evaporator coil is reading abnormally low. This usually happens because the filter or the coil behind it is clogged with dust and pet hair, blocking airflow and making the coil freeze up.
FIX Unplug the unit first. Slide out the washable air filter from the top or side grill. Rinse it under cool water and let it dry completely. While it's out, use a vacuum cleaner hose with a brush attachment to gently suck all the dust and lint from the coil fins you can now see. Plug the clean, dry filter back in, plug the unit in, and try it again. Give it a few minutes to clear the code and restart.
IF THAT DIDN'T WORK If the E2 comes back quickly, the sensor itself might be faulty or the internal drain pan could be full. Check that the unit is perfectly level—if it's tilted, water can't drain to the pump and might trip the sensor. Use a small level on top of the unit and adjust the casters or the surface it's on.
HEADS UP Never run the unit without the filter installed. That lets even more debris into the coil and can cause permanent damage. Clean that filter at least once a month during heavy use.