No drain pipe is installed.
Sometimes, in order to save time, air conditioner installers do not install plastic drainage pipes, which leads to water leakage in the outdoor unit of air conditioner.
Low pressure pipeline condensation
When the air conditioner starts heating in winter, the water flowing from the drain pipe of the indoor unit is a suction pipe or a low-pressure pipe. In winter, the pipeline is ice, which forms condensation after hot and cold exchange with outside hot air, and then forms water droplets from less to more, which will lead to water leakage.
Installation position is incorrect.
The water leakage of the outdoor unit of the air conditioner may be because the indoor unit is low on the left and high on the right, and it is not level with the wall.
Pipe blockage
The outdoor unit may leak water due to bent drainage pipes, loose joints and blocked pipes.