The automatic climate control is designed to be set at any comfortable setting & left there. The whole idea is that you don't have to reset the temperature all of the time. There is a sensor in the dome lamp area that is responsible for most of the temperature corrections, possibly it isn't doing the "job"!! Are you using the "EC" mode alot?

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MERCEDES BENZ MASTER GUILD TECHNICIAN
ASE MASTER TECHNICIAN
27 YEARS M.B. TECH