Focus mk3 facelift AC

Hello everyone,

My AC is the manual one  found in base models. The problem is that my AC feels weaker than last summer. It happened after a dealer changed my filter with an expensive one, which seemed to reduce airflow. I bought a cheaper filter and the airflow improved but  when it's very sunny i feel that the cold air that gets out of the vents is mixed with some warm air. When i turn off the AC i  still have  non cold air flow going out from the vents for few minutes. 

The AC still works but i can i say the cooling effect that i get now in position 3 is the one i used to get in position 2, even the smell slightly changed and it no longer smell as fresh.

I wonder if any of you experienced a similar issue and how it got fixed. Is it possible the dealer messed with something?  I also wonder what is the type of the original filter sold with the car , hepa or something else?  how often you regas your ford focus AC(some say never) and how the ac is generally maintained?

Thank you