I've got a home that was built in 2000.
I'm largely unfamiliar with AC systems, so you'll have to excuse my
ignorance.
Outside my home, I have two drains - one on the upper floor and one on
the lower floor.

I "believe" I've got a problem - currently, only the upper drain is
dripping water.

Can anyone tell me the difference between these two drains? I see two
PVC connections on the unit in my home, but haven't opened it up to
tell the difference.

Research tells me that one is an "air handler" and one is drip pan
overflow... Does the pan backup the air handler?

I can attempt to clean it out, but I'd like to know that I do have an
issue first before spending time on it..