Disparity in output of AC

Summer question: Climate control set in AC mode. Temp. setting at 65
degrees for both sides (not on "Dual"). Suddenly noted air coming out of
driver's side vents is quite warm, almost heated. Air coming from passenger
side is still comfortably cool. Tried all fan speeds, no difference. Then,
decided to go up on temp. setting to around 80 degrees and back down
again to previous setting of 65. Cool air was now noted to be coming out of
the driver's side vents again. It continued to remain cool for the remainder of
the trip, but I have not checked it again since then. Not sure if condition will
return. Do you have any ideas on this situation?