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.Google+
Car Problem Reports
Mercedes-Benz E420 Malfunctioning Regulators May Cause Blower Motor Failure
Mercedes-Benz E420 Problem
Model Year Affected: 1997
Average Mileage: 154,000 mi (99,000 mi - 245,000 mi)
Visitor, 1997 Mercedes-Benz E420, 245,000 mi
Mercedes Benz forum had me use another resistor assembly,works good now.
Blower motor regulator replaced with S-class unit, in order to avoid replacement of blower motor as well.