Who didn't hear it? "My automatic air condition is broken and I was told I should change the heater control valve. Mercedes asked for 1100 Euros and still it does not work. What shall I do?" Even A/C professionals refuse to repair 1st series automatic A/C system of Mercedes-Benz.

First series automatic climate control is based on Chryler's Auto-Temp II climate control introduced in 1971. It uses Chrysler's control valve and amplifier, vacuum control is however different. If you like, have alook at Chrysler Imperial Website.

We will just analyze the electrical part of this type of air conditon and remove possible failures. I assume that you have a WIS-CD (workshop manual)  and have already applied test 83-601 „Quick test without tester and remedies“. If this testhas told you to try and replace the heater control valve or the amplifier (comparator) then this article is right for you.

Pic 1: Control Panel from a MB R107 500SL
Pic 1: Control Panel from a MB R107 500SL

Even if labels are in English and °F degrees, it was also installed in European cars! Merceds-Benz also used an US supplier for that!

There is a quick test on WIS-CD with number 83-601 „Quick test without tester and remedies". That is a really good test procedure, but often enough it demands that you replace control valve or amplifier for a try. Even chapter "A/C and automatic A/C control" on WIS-CD mix all different systems that were installed in MB R/C107, W116 and W123 at any time. So that includes my manual A/C of my 73 450SL as well as A/C automatic control systems of late 70s and 80s. We will investigate in detail the root problems of 1st series automatic A/C systems.

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Dr-Djet (Volker)

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