DIAGNOSIS Mineral scale and dust build up on the evaporator and condenser coils inside, drastically reducing efficiency and causing ice-up.
FIX For a basic clean, power off and unplug. Remove the water tank and the rear air filter. Use a vacuum crevice tool to gently remove dust from the coils you can see through the grilles. For scale, use a spray bottle with a 50/50 mix of white vinegar and water. Lightly mist the coils (don't soak the electronics), let sit for 10 minutes, then wipe accessible areas with a soft cloth. Let everything dry for an hour before restarting.
IF THAT DIDN'T WORK If performance is still poor, the drain ports might be clogged. Locate the continuous drain outlet at the back. Use a pipe cleaner or small brush to clear any debris from the hose connection point inside the unit.
HEADS UP Never use harsh chemicals, abrasive brushes, or high-pressure water. You'll bend the delicate fins on the coils, which is worse than the dirt. Do this cleaning at least once per season of heavy use.