2012 GMC Acadia AC won't blow cold out of all vents

My 2012 Acadia has never great AC but now the passenger vent and the right vent of the 3 in the middle plus the vents in the rear are blowing ambient temp air. The driver vent and 2 of 3 vents in the center are cool. Passenger controls are on and temps set to the minimum. What’s going on?

There are little motors in the AC system that open and close doors that direct the air. One of them has gone Tango Uniform - In other words, it is broken. Common problem although a bit early.