You need to replace blower motor controller located inside the passenger side dash board. The controller is about $25 on eBay and about 1 hour of work. Have your torx tools ready.
https://mbworld.org/forums/e-class-w210/153918-early-w210-blower-motor-regulator-replacement-diy-here.html
I think ur 01 falls under the late design so the components looks slightly different.