A malfunctioning HVAC blower motor regulator can cause the blower motor to operate below the requested speed or not at all. Updated regulators are available; the blower motor and cover need to be replaced at the same time to upgrade the system.
Car Problem Reports
Mercedes-Benz E320 4MATIC Malfunctioning Regulators May Cause Blower Motor Failure
Mercedes-Benz E320 4MATIC Problem
Visitor, 1999 Mercedes-Benz E320 4MATIC, 110,000 mi
Strange erratic blower and A/C functions. Sometime it would blow strong but then stop, then back to strong with very little change in car cabin temperature or A/C settings. Only happens when using cold AC.
Sometimes the a/c does not turn on, other times it does.