Factory A/C was uncommon, especially on Euro cars; most systems were US dealer-installed under-dash units (Frigiking, Kuhlmeister, Behr). Owners note retrofitting R134a into the old R12 systems is possible but leak-prone, while adding a compressor is not especially difficult or expensive.
Air conditioning: dealer-installed and largely aftermarket
Mercedes-Benz W111 Coupe / Cabriolet · ownership