One simply item to check are the flexible rubber connector tubes under the hood, near the fuse box/firewall area.
I helped a friend whose 190e had heat coming out the outside vents I believe while AC out the center.
His were cracked. Simple replacement.
You may want to try a search. There are many postings on the topic.
'03 E320 Wagon-Sold
'95 E320 Wagon-Went to Ex
'93 190E 2.6-Wrecked
'91 300E-Went to Ex
'65 911 Coupe (#302580)