Piecing together an A/C system

OP is in Austria. EU banned R-134A for new cars in 2013. https://europe.autonews.com/article/20130824/ANE/130829947/toyota-switches-back-to-banned-refrigerant-in-europe . But, it can likely still be bought to service older cars. Caused a big stink after a M-B test showed R-1234yc can burn to produce extremely dangerous HF gas (etched glass windshield, worse for your cornea). Not that R-134A is better since it forms deadly phosgene gas (used in WWI). While the refrigerants themselves don't easily ignite, a leak comes with an oil spray which will ignite if it impinges on a hot exhaust (M-B test w/ turbo). Also, if the engine is still running after a front crash breaks the condenser, leaking refrigerant is sucked into the engine to burn. Firefighters have been gassed in passing an exhaust pipe.

Venting HC refrigerant is no worse for the planet than cow-farts (a major concern), but illegal to vent any refrigerant per EPA. So, watch for an EPA drone hovering if you do have to vent it. For 20 years, the EPA has still been "evaluating" HC refrigerant, reportedly because it can burn in air. It is illegal to directly convert from R-12 to HC. You must first install R-134A, recover that, then install HC refrigerant. Again, watch for those drones. If in CA, consider that the western U.S. hasn't had an average temperature increase since records began, nor most of the Pacific, equator, and southern hemisphere. Most temperature rise has been in the Arctic (4x) to drive up the global average, and in northern Europe. Using R-134A (bad for global warming) risks causing the Inuit to shed a layer.