I believe what you have is the best AC unit available on a MB.. for sure the most simple....
I think there are three AC configurations on the 123 cars... manual control by wire, and AutoClimate control in versions I and II.
The latter are recognized by the wheel type temp control.... and are WAY to complicated for mere mortals to trouble shoot... so I think you got really lucky.. now if you just had manual windows, manual shift and no sunroof you might just have the perfect car.
The reason I think they are too complicated is that I own a paper copy of the MB heating and airconditioning manual.... those last two types will BOGGLE your mind with their complexity.