The ACCII (Chrysler-based, aka the "evil servo) system was a crime against nature. MB engineering was undoubtedly pushed by marketing to come up with an automatic climate control to match the US domestic offerings. In a collaboration that was only a harbinger of awful things to come 20 years later, they reached out to Chrysler and they (probably as a joke) sent them the design for the ACCII. It was used up through 1980.

Starting with the 1981 MY up through the early 90s they used the ACCIII (with the horizontal buttons).

If you have the ACCII there are solutions out there to get it going again but they are very expensive.

If you have ACCIII that is one of the finest examples of analog control engineering out there. It is not difficult or expensive to get it right again. The troubleshooting procedures are located online for either the 123/early 126 or the successor 124/late 126 version.

Most of the time the problem is a bad temperature sensor or a leaky actuator pod.

I'm an originalist, my goal is to try to keep the car as original as possible yet be practical about it. It's a testament to the engineering that went into these vehicles.

__________________
The OM 642/722.9 powered family
Still going strong
2014 ML350 Bluetec (wife's DD)
2013 E350 Bluetec (my DD)

both my kids cars went to junkyard in 2023
2008 ML320 CDI (Older son’s DD) fatal transmission failure, water soaked/fried rear SAM, numerous other issues, just too far gone to save (165k miles)
2008 E320 Bluetec (Younger son's DD) injector failed open and diluted oil with diesel, spun main bearings (240k miles)

1998 E300DT sold to TimFreeh
1987 300TD sold to vstech