All the components like solenoid, blower are probably driven by the nominal input voltage. They can accept a range of voltages, so any voltage drop along the wiring does not matter. The control is probably TTL logic driven at 5v ( I do not know for sure, don't have access to schematics. ). The voltage regulator in the CCU would regulate it down to the designated voltage in any event. So the voltage drops the OP observed is just normal wiring drop or caused by junction resistance.

__________________
Not MBZ nor A/C trained professional but a die-hard DIY and green engineer. Use the info at your own peril. Picked up 2 Infractions because of disagreements. NOW reversed.

W124 Keyless remote, PM for details. http://www.peachparts.com/shopforum/mercedes-used-parts-sale-wanted/334620-fs-w124-chasis-keyless-remote-%2450-shipped.html

1 X 2006 CDI
1 x 87 300SDL
1 x 87 300D
1 x 87 300TDT wagon
1 x 83 300D
1 x 84 190D ( 5 sp ) - All R134 converted + keyless entry.