Unfortunately, you found your car before you found us.

Yes, they did use a Chrysler control system on 300Ds from 77 to 80 and 78-80 W116 300SDs (as well as gassers like the SLs in the 70s). They went to an MB made system in 1981 that is somewhat better, but still irksome. The 240D and the euro cars have the most DIY - friendly system. People have fixed a lot of these units by themselves, so it can be done. There is a new electronic version for $600 or so that replaces it.

But here- look at the Auto-temp stuff at the Imperial site to get an idea of what you have.

http://www.imperialclub.com/Repair/Air/index.htm

Rick

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80 300SD (129k mi) 82 240D stick (193k mi)77 240D auto - stick to be (153k mi) 85 380SL (145k mi) 89 BMW 535i 82 Diesel Rabbit Pickup (374k mi) 91 Jetta IDI Diesel (155k mi) 81 VW Rabbit Convertible Diesel 70 Triumph Spitfire Mk III (63kmi)66 Triumph TR4a IRS (90k mi)67 Ford F-100 (??)