Hello DG,

I'm an HVAC Contractor in middle tenn, and normally you're right on,
one is the coil drain that is usually wet during the summer, the other
is connected to the aux overflow drain pan and can tell you when you
have a problem, but, you say "one is on the upper floor and one is on
the lower floor", if you have 2 indoor air handlers, and the lower
unit's cooling is running, then you're lower floor drain might be
clogged.