The voltage that you see from the actual value screen is not the voltage to the blower. It is the control voltage to the end stage amplifier that controls the blower speed - blower regulator.

If you view the blower regulator as a transister amplifier, the control voltage would be that which goes to the base of the transistor. The current carrying legs of the transistor are inserted into the ground leg of the blower motor.

Transistors can be used as gates or as amplifiers. In this case the transistor is being used as an amplifier. Higher voltage on the base translates to larger current flow across the transistor bridge. In effect it looks like a large variable resistance, resistor.

The original end stage was insufficient for the extended loads and the whole devise was redesigned in the 210 chassis (was the same in the 210 till 1998). it was never redesigned for the older 140 chassis. However, Behr has on its own redesigned the regulator and since we have started using them we have had no short term repairs. (high current in old blowers killed a few of the original design regulators in the warrantee period, for a period we).

If you look at the possibilities on fastlane you can see that the Behr is more money. I would definitely chose the Behr.

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Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician