My 95 E300D, which I've owned for 8 months, has suffered from weak airflow and a noisy blower fan. Heating worked fairly well but cooling has been inadequate. All climate control modes operate correctly, so I did not suspect vacuum pods or the CCU.

I opened it up today and sure enough, the Bosch blower motor had been installed backwards. The mounting bracket is supposed to prevent this, but the entire assembly had been turned 180 degrees. Brushes are in good condition so I lubed the bearings, installed the motor correctly and now have amazing airflow, a lot less noise and great cooling.

Zeitgeist over on BenzWorld has a thread titled My Climate Fan Saga, which alerted me to this possibility. He has included great pics of the proper orientation of the blower motor.