Yes, there is an improvement that can be made, and its called a parallel flow condenser. They are sold very inexpensively at this site (although some custom work will be necessary to mount it and hook up the hoses):
Your question is asked quite frequently at www.aircondition.com,
a technical webpage for automotive a/c, and this is the common answer. You also need to make sure your electric fan works properly. I know most new cars are wired to turn on the electric fans when the a/c is on. Are Mercedes the same way? I am currently rebuilding my a/c, so I don't know yet how the electric fan works, but if it doesn't run at all times when the a/c is on I think I will wire it so that it does.