Naturally when it gets hot outside you turn on the air conditioner. When it is humid outside, a byproduct of cooling the air is condensation. The more humid it is, the more condensation will be produced. The condensation drips off of the coil and into a condensation pan underneath the unit. The condensation is then carried out of the pan by a drain line to the exterior of the house. So what a homeowner will occasionally see is water dripping from a small PVC elbow coming out of the house.
A common call I get is about this very issue. People will call and say they have a plumbing problem because water is coming from a pipe that normally doesn’t have water coming out of it. Yes, that is by design. I try to tell people that this is exactly what should be happening when you are running the air conditioner and it is very humid outside.
What you may notice is the condensation pan will leak and you will develop a stain on your ceiling. This of course is not normal and needs attention. This will lead not only to a repair of some type on the pan or unit, but also a repair on your ceiling to make the stain go away.