Air Conditioner - Drain Plug
Room air conditioners are not designed with a drain plug that allows the unit drain excess water while operating. Air conditioners have a "slinger ring" around the rear fan blade. The fan is designed to pick water up off the bottom of the pan and throw it against the condenser coils. This design feature helps improve the efficiency of the unit by reducing heat on the coils, and helps remove some of the condensation and rain water from the pan.
Water will collect in the base pan and may even overflow and drip outside during periods of high humidity or on rainy days. This is normal operation.
Some room air conditioners appear to have a drain plug at the bottom of the pan. Under normal circumstances, this drain plug should not be removed. The drain plug allows water removal if the air conditioner is being stored for the season, or if a technician needs to remove the water.