The control voltage from the A/C pushbutton should be between 0.8V to 7.0V depending in selected blower speed.
The blower regulator is a HIGH rate failed part! MAKE sure to keep a fresh micro-filter in the car as they can cause blower failure when they get clogged.

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MERCEDES Benz Master Guild Technician (6 TIMES)
ASE Master Technician
Mercedes Benz Star Technician (2 times)
44 years foreign automotive repair
27 Years M.B. Shop foreman (dealer)
MB technical information Specialist (15 years)
190E 2.3 16V ITS SCCA race car (sold)
1986 190E 2.3 16V 2.5 (sold)
Retired Moderator