A/C- blows warm air on the drivers side and cold on passanger side

The a/c in my '03 mercury moutaineer blows warm air on the drivers side vents, but cold air on passenger side. The dual center vents are half warm and half cold. Is a duct or vent stuck?

Quite likely.

Maybe a disconnected or stuck blend duct door.

Are your heating/a/c controls vacuum operated or linkage?

If vacuum, make sure there are no damaged or disconnected hoses.