DIAGNOSIS Internal condensate is not being directed to the drain bucket or hose. The most common cause is a disconnected or kinked internal drain tube.
FIX Unplug the unit. Remove the rear exhaust hose assembly. Carefully remove the rear plastic shroud (several screws). Inspect the clear plastic drain tube that runs from the evaporator coil to the drain bucket. Re-seat it if loose. Clear any blockage.
IF THAT DIDN'T WORK The drain pan under the evaporator coil could be cracked or the foam seal around the coil housing could be degraded, allowing water to bypass.
HEADS UP This is a complex disassembly. If uncomfortable, call a pro. Ensure the unit is perfectly level front-to-back and side-to-side after reassembly.