I am going to tackle a climate control problem on a 81 300D. Noithing works when I hit anyone of the problems. I have printouts to test all the components but what are the common causes of climate control failure?

Also where can I get the special mercedes tool that is needed to test some parts of the climate control?

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

What exactly are you experiencing? There are a multitude of problems that can affect the way your system works, as there are many parts of the system. If you list the symptoms you are having, we can help you a bit more. BTW, I myself am in the process of rebuilding my system, and should be finishing it up this weekend.

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1989 300E 144K

Nothing works on the climate control. I can hit any of the buttons and nothing will work. I am foreseeing I will be there a while hunting it down.

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

One of the more common reasons for what you have described is that your control unit needs resoldering. Over time, the solder cracks where the three circuit boards are joined, preventing any response from the unit.

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Dave
1983 300D Daily Driver