Hello...
Refrigerant can be added by any qualified service center,
however, they first must check the system for leaks, and fix them, before adding.
It is unlawful to add freon to a leaking system.
The VCC code is related to your transmission.
I have never had code E90...
These problems can sometimes be difficult to isolate, as the transmission is complex.
There are switches and solenoids inside of the transmission and you will have to drop it to R+R.
Are there any driveability issues?
It may be that the VCC (Viscous Clutch Converter) isn't receiving the signal to either turn on/off.
There is a test you can perform to see if the VCC turns on/off.
(apply the brake lightly while driving above 45(?) and you can feel the VCC turn on/off)
Use the search feature to find out more details.
Usually you will not notice when the VCC engages/disengages.
(you will only notice a slight increase in RPM's and 1%-2% lower MPG's).
Post back your solution.