Regarding the original post (before we got off on a tangent by trying to repeal the First Law of Thermodynamics ), is this a common problem, or a known design issue, with W124 climate controls? My W123 control (rebuilt) seems to do a pretty good job of operating the fan at the appropriate speeds in auto mode. It seems to me that it would be easier to replace the control unit with a rebuilt unit if it's not functioning correctly. If the unit is acting up and causing the fan to run at the wrong speed, attemping to redesign it may just make things worse. Assuming this is not a design problem, it appears that changing the design of a semi-failed component without fixing the underlaying problem is a short term solution at best. Just my 0.002.