Why does an air conditioner vent sweat

You have reached the dew point and at that temperature, the air cannot contain that level of humidity. In essence, it rained on the vent. Lower the humidity with a dehumidifier or raise the temperature.

It is very dirty and if not cleaned the compressor will have its valves ruined and it will work badly. Take unit out of window and remove covers that cover the coils. Spray down with foaming Easy-Off oven cleaner keeping it away from electrical controls and capacitor. Wash out many times until it is very clean turn on side to dump out water; it will not hurt it. Make sure drains are clear. Let dry in sun and reassemble. Put in good filter and you are good to go. Repeat every year or six months as needed. DrTom4444

If you have a central system and your vents are sweating then the cause is the same: dirty coils. You need someone to come out and clean the coils and blower fan. DrTom4444