A/C vents blow warmer air on passenger

[StartX5]

Hi all - just past summer, my X5's air condition was not working good. AC vents blow warmer air on passenger. Driver side vents blow icy cold while 9F warmer on passenger. And when the AC was on and the car was parked, i saw alot of puddled liquid (condensation water) under the car.
I added freon and it was full, however the problem still the same.
I search in the forum and most of problem due to evaporator and heater valve. If it's heater valve, it's a big job since we have to remove the dash in order to replace the heater valve.
Does anyone experience this problem?
Thanks!