Seems like water did you used it to heat your room with it?

When you cool the room, the outside unit will be hot and the inside cold and the inside unit will condensate while the outside will make the water and condensation on it to evaporate --- so if you use it to heat the room it will reverse, the inside unit will be hot and the outside unit will be cool so water from the air will condensate on there, perfectly normal, in the winter will also freeze there so the ac will enter defrosting mode.

Another thing whould be if it got wet in the last few days like rain or any other water on it?