AC Hot on one vent only

[Ferguson]

2007 X5 4.8l, it's always been a bit wimpy in the AC area, but finally measured something.

Of the four vents in the front, with the AC running after about a 10 minute drive (car previously pretty), measured these temperatures:

Driver left vent: 60 degrees
Driver right vent (center set, left side): 61 degrees
Passenger left vent (center set, right side): 82 degrees
Passenger right vent: 71 degrees

While the far right vent was too warm, the 82 is the real problem.

I cycled to heat on that side (cranked just right side to 85 degrees), and both right vents got quickly very hot (I did not measure). Cycled back, in 30 seconds or so it was back down to 82-83 degrees.

As I ran it longer, it cooled, but what I think I'm getting is ambient temperature out of that vent, so as the car overall cools, that vent cools a bit.

What could cause one vent to not be cooling? Is it anything user fixable, e.g. some damper that is fairly accessible?

I've got a few months left on extended warranty so probably will just take it in, but if it's something simple I'd like to just fix it.

PS. I think it's probably been this way from day 1. The car is always slow to cool, but my wife is cold natured and turns the vents away from herself, and would never complain about warm air even in summer. But I think loss of this important center vent's cooling may be contributing to how slowly the car cools.

PPS. I didn't measure the back vents, but by hand they feel slightly warmer on the passenger side also, but both felt like cool air. I.e. more like the 71 above, not 82.