1984 300cd........the heater blower stays on high no matter what buttons i push including the off button.i just rebuilt the mono valve,put a new aux pump on and put a different(known to work)ccu unit in and still having the same problem.what function does the blower regulator provide? could this be the culprit?
i did do a search and found a few things but nothing i havnt already tried.
thanks...........

If you push the off button and the blower stays on high...........the CCU is the culprit.

The blower regulator controls the voltage to the resistor bank to select the desired fan speed based upon input from the CCU.

the ccu unit i tried was from my wifes 300d and it seems to work perfect in her car but the blower still stays on in my car.it seems very odd but i can try a differtent ccu also.
im thinking about wiring a reostat in-line in the blower motor if i cant figure it out......thanks much

blower motor resistors in the engine compartment. yes the ccu sends the signal to the resistor to select what speed but if say if low resistor is shot then the blower motor will blow high because the ccu sent the signal to turn the motor on.

btw im in ct as well

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1986 300SDL, 211K,Dealership serviced its whole life
1991 190E 2.6(120k)
1983 300D(300k)
1977 300D(211k)

^^^ I second checking the pre-resistance group located on the passenger side fenderwall forward of the coolant recovery tank.




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1983 123.133 California
- GreaseCar Veg System

After replacing the ccu,blower motor resistor on the fender and the temp control relay(silver box) the only thing left was the blower control relay(black box) and that did the trick.i was running out of options.
Is there a shop manual the gives you testing options on mercedes electrical? I hate throwing money at it in hopes that i will find the problem.......thank!

Oddly enough, it's called the Electrical Troubeshooting Manual.