I have installed 2 new window type AC units in the past 2 years and neither one had a drain hole. I very carefully located a area near the back where drilling a hole would not hit any vital parts and drilled a small drain hole there. On high humidity days water pours out the hole. Without it the water would pool inside the unit and I'm sure it would be the perfect environment to grow mold. Why they don't install a factory drain hole is beyond me. The older units used to have them.