Is it on a slope to the rear,if not it should be about twice the slope the manufacturer specifies.
Most do have a drain but from memory a few don't and rely on what 4bee said.
The drain could be out the rear or just a hole in the baseplate.
Usually the baseplate is full of rubbish and needs a good clean out,which entails removing the unit,taking off all the panels and cleaning it paying good attention to the water drain holes and channels,then refit and all should be good.Paintbrush and water with a cleaner helps,maybe Truck Wash?And keep any water or cleaner well away from the electrics and fan motor.
Oh,and while it is out check the slope of the case.
I am presuming its a box roomy AC unit?
EDIT...just saw Tombies post which answers everything loud and clear.[biggrin]

