Every air conditioner condenses water out of the air it cools. A window unit drips it outside; a portable unit has no outside, so it collects the water inside, evaporates as much as it can into the exhaust air, and stores the rest in a tank. When the tank reaches its level the unit stops cooling and displays FL, or on some models CH04. LG's own guidance is that how often this happens depends on the humidity of the room, and that a unit which fills quickly in muggy weather is doing its job.
Reading the Frequency
In a dry climate a portable unit can run for days without FL, because its self-evaporation keeps up with the small amount of water it removes. In a humid basement or a coastal summer, the same unit may fill in a matter of hours. The frequency of FL is a measurement of the room, not a symptom of the machine. It becomes a symptom in two situations: when FL appears and the tank is nearly empty, and when FL never appears while water runs out onto the floor.
Emptying the Tank
Switch the unit off and unplug it before you do anything with the drain, because you are about to tip or open a cabinet containing a compressor, a fan motor and live terminals, and water and mains do not mix. The drain outlet is usually a capped port low on the back. Move the unit to a place where a shallow pan or a floor drain can take the water, place the pan under the port, remove the cap and the plug, and let it empty; some models must be tilted slightly toward the port to drain fully, which is why the unit is unplugged first. Refit the plug and cap firmly, plug the unit back in and restart it.
Continuous Drain Instead
Most LG portables accept a hose on the drain port so that condensate runs off continuously and FL never interrupts cooling. The hose must run downhill the whole way to a floor drain or a pan lower than the port; a hose that rises, loops or lies flat in a coil holds the water in the unit and brings FL back. Keep it short and secure it so it cannot pull off the port. A unit with a hose fitted that still shows FL almost always has a hose problem.
The Exhaust Hose Matters Too
Warm air leaves the unit through a large exhaust hose to the window kit. A long, stretched or kinked exhaust hose makes the unit run hotter and less efficiently, so it condenses more water for the same cooling and fills faster. Run the exhaust hose as short and as straight as the kit permits and seal the window panel so warm outside air is not drawn back in.
When FL Is a Fault
If the display shows FL with the tank freshly emptied, the float switch that senses the water level is stuck, or its connection has failed. If water leaks from the cabinet without FL ever appearing, the float is stuck the other way, or the internal drain pan is cracked or blocked with slime. Both are inside the chassis, next to the compressor capacitor, and both are technician work. Book an LG portable air conditioner repair and describe how quickly the tank fills, whether a drain hose is fitted, and what the room is like.