THere is no filter for the H/VAC system in the (W201).
Maybe check for restrictions & to see if the duct work is snapped together correctly.
1994 E500 (MY SUNDAY DRIVER)
1993 190E SPORTLINE LE W/ M104 SWAP
2000 BMW 528I (WIFEY'S CAR)
"Excuses are crutches for the unfounded."