A/C issue question. Drivers vents warmer...FIX = ADD FREON

[ACQB]

After reading multiple posts, not sure what needs to be done on our 2003 Explorer XLT. Manual controls WITHOUT dual front zone control. Has rear manual controls in the overhead con'. As I said, after reading several posts, not sure where the issue lays.
Symptoms/Issue:
Turn A/C on either normal or max, set temp to coldest on both dash and overhead, passenger side vent, right center con' vent, rear vents all blow ice cold. Drivers side far left vent and left center vent blow slightly warmer. Its not 'hot', its just not as cold. Very noticeable if its hot & humid.
Turn temp to hot and they all blow the same. HOT! At least can't tell any temp' difference with a bare hand.
Turn temp back to max cold...Passenger & rear vents blow ice cold, drivers vent and left center vent again blow slightly warmer than the others.
What would cause this?Help??
Thanks in advance.

 

[ACQB]

Took a flier and added Freon. Pre-charge after a 10 min drive, Passenger side was blowing 52F, Drivers side was blowing 61F according to my probe thermometer. Only took slightly more than half a 14oz can, all vents now blowing a very frigid 48F post charge.