We have just replaced the climate control module along with the blower motor on a 1983 300D 123 Mercedes. Everything appears to work except the blower switch on the right - where you can select high or low. When we select one of them, the blower turns off. The blower works in automatic mode. Is the module itself faulty, or should we look elsewhere? thank you!

Which "Module" did you replace? There are 3 pieces to the climate control system: The pushbutton unit in the dash, the silver "temperature regulator" box behind the dash, and the black fan relay box behind the dash. The silver box is the "brain" of the system and is your most likely cause for intermittent or flaky operation.

__________________
Current stable:
1995 E320 149K (Nancy)
1983 500SL 120K (SLoL)

Black Sheep:
1985 524TD 167K (TotalDumpster™)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)

Thank you. We replaced the push button unit in the dash. We will look into the temperature regulator box, but the "auto" temperature is working which to me sounds like what the temperature regulator box would be for (for all I know ) - it is only when you take it off of automatic that it doesn't work.

Does the fan actually ramp up and down in speed when in "Auto"? Does the fan speed reduce or increase in reaction to the temp wheel? If not, the silver box is your suspect. Having been through similar issues on a number of cars, not once has it been the pushbutton unit yet. It's just some switches and relays, there's no actual "control" to speak of, that all lives in the silver box.

__________________
Current stable:
1995 E320 149K (Nancy)
1983 500SL 120K (SLoL)

Black Sheep:
1985 524TD 167K (TotalDumpster™)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)

Diseasel, it does ramp up - haven't run it long enough to see if it ramps down. We'll just look at replacing the silver box as this ac/heater has always been quirky and has a mind of it's own.

Look up a member on this forum with the username "James Dean", he repairs climate control modules.

__________________
Current stable:
1995 E320 149K (Nancy)
1983 500SL 120K (SLoL)

Black Sheep:
1985 524TD 167K (TotalDumpster™)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)

Thanks!

There was also an outfit in Tennessee (whose name I can't recall!) that rebuilds the units. Helluva nice guy. I bought one from him for my 190D about 8 years ago and it still functions as it should. If I can recall the name for find the invoice, I'll post, but a Google search might locate him.