Water from the evaporator, normally would run down a pipe, from a trough along the back of the unit, the other end of the pipe, would feed into a trough around the top of the compressor. Heat from the compressor would then evaporate the water away. Check the pipe is not blocked. poke some wire or similar down, not to stiff, as you might damage it. other than that, make sure that the trough along the back inside, If a separate unit is positioned correctly, Some are part of the moulding. Should be no other reason for it happening.
SD, March 2012