Why are the ducts from my heater leaking water?

Sweat,, are they insulated?

Its like a cold glass of ice water sitting in a warm room,sweats

No, not insulated, but would they sweat inside? It's dripping from where the ducts connect. There's a hose from the main system that leads to a drain. Could it be that this part is non functioning, and so the liquid has no where else to go but into the ducts?