I am only remotely familiar with the manual controls (only Tempmatic in US). I think it is like a thermostat. It will change the cycling temperature. This will have absolutely no affect on your system if it doesn't cool well enough to cycle.
Be sure that the recirculate door is workin properly as it will raise the duct temp by 10deg F if it isn't.
Bosch Master, ASE Master, L1
33 years MB technician