A water stain on ceilings near ducts may point to condensation, drainage failure, or a disconnected line

https://www.slideserve.com/katterobac/hvac-emergency-signs-that-point-to-a-serious-system-breakdown

A water stain on ceilings near ducts may point to condensation, drainage failure, or a disconnected line. Turn off the system and inspect carefully before calling for repair.