With high fan speed selected, voltage supplied to motor should be > 6 volts. Check blower motor regulator.

Inspect cabin air filter; clogged filter reduces air volume available to blower motor.

FYI, W210 is equipped with cabin air filters and activated charcoal filter.

Do a search for JimF. Start with "A/C blower's output is low..." That will help you with the regulator. JimF also has a site which covers retrival and interpretation of W140 AAC DTCs.