The blend doors may give trouble. Depends on the year and model you're asking about.
Which Buick and what type of system? Dual temp controls?
Some cars would give warm air on one side in hot climates because the freon was low. E.g., the 2000 and up leSabres (H-body) would use all the cooling on the part of the evaporator before the freon got to the coil parts that the air went through going to the driver. This was true on single or dual control.
If the problem is hot days, and on cold days the blend door(s) modulate the temp up and down when using heating, likely the blend doors are okay.
That's a good first step actually---to check the freon charge. So maybe putting a temp gauge in the AC vent that's working to see how cold it's getting.
Answers
Which Buick and what type of system? Dual temp controls?
Some cars would give warm air on one side in hot climates because the freon was low. E.g., the 2000
and up leSabres (H-body) would use all the cooling on the part of the evaporator before the
freon got to the coil parts that the air went through going to the driver. This was true on single
or dual control.
If the problem is hot days, and on cold days the blend door(s) modulate the temp up and down when using
heating, likely the blend doors are okay.
2014 Malibu 2LT, 2015 Cruze 2LT,