The fresh air door is at the bottom of the heater box! Behind the ash tray by about 18". The door is 100% open in the fresh air(no a/c) mode & also in any heating mode. It is 80% closed in the normal A/C mode & will close 100% in max A/C. There are 2 vacuum lines that control operation!!

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MERCEDES Benz Master Guild Technician (6 TIMES)
ASE Master Technician
Mercedes Benz Star Technician (2 times)
44 years foreign automotive repair
27 Years M.B. Shop foreman (dealer)
MB technical information Specialist (15 years)
190E 2.3 16V ITS SCCA race car (sold)
1986 190E 2.3 16V 2.5 (sold)
Retired Moderator