Hello,I will be glad to try and assist you with this,Welcome to Just Answer.
ok the reason why one side is cold and the other isnt is because the vehicle is low on freon,it will cool one side but not the other when it gets low as there isnt ebough freon to cool both sides and the closest side of the vehicle to the evaportaer will blow cold and leave no cool airflow for the other side.
The vehicle shouldnt need recharged once a year(bogus)once a system is charged and if the vehicle keeps the freon in the system(no leaks) then it should only have to have a one time charge unless another leak has sprung.
What needs to be done is the system needs to be checked for a freon leak,if the freon was recharged last with dye added then someone with a dye detection light can look over the ac system to find where the freon is leaking out at.
Some of the most common are the condensor,and ac compressor as well as possibly a freon line/hose.
If dye hasnt been added to the system then the system can be pressurized with nitrogen up to 200 psi or 250 max to see if the leak can be pinpointed,you should hear it hising out if the leak is signifigant enough,also the components in the ac system can be checked over for oily residue leaking out around hoses and components,if residue is found then this would indicate the area of the leak.
It definately sounds like it from here that the vehicle is low on freon again and needs to be checked for a leak in the system then recharged one last time once the leak is found and corrected.
I hope this information helped,If you need anything else let me know,If you feel satisfied that I have assisted please click accept as this is how I get paid,positive feedback is appreciated,Thanks Pete.