My shop fully charged my system that was not blowing very cold (cool) and it is no better. Now they say it could be the filter which has probobly never been replaced in the past 40-50K. Do you think this could affect the temperature of the system very much?

the central flap motor might be going, mine is. then the flap doesn't close all the way and some warm air gets in. I know S4s didn't come with filters, and I don't think S6s did either, plus that would just cut down on airflow

the compressors in the c4 , are prone to failure -- you might want them to check the orifice tube filter[also called the restrictor] for metal debris!!