a/c
#1

i have water coming in ceiling,and drain has hardly ever had water drain.the plenum is water soaked?
#5
24 years old ?
take the cover off the coil compartment, and check the pan. if no one has disturbed the coil (repositioned it, maybe if changing the furnace) my money is on rusted pan. if unit were freezing up, due most likely to low charge or restricted airflow, water will overflow the pan......but 24 yrs old, i still say the pan....let us know