[Matt B]

I did the conversion today. Following most suggestions I used PAO oil (which nicely blends with R12 mineral oil) following the shop manual guides.
I replaced the dryer by an AC Delco genuine part and added 105ml of oil into the inlet pipe. Pulled vacuum for 2 hours, system is extremely tight, no vacuum loss at all after 5 minutes.
Than I added 420gr r134 with the engine running and A/C "off". At 420gr I switched on the A/C as described in the manual and added another 420gr to reach 840gr as suggested by Thomas.
Operation worked perfectly well, but: the A/C doesn't cool. Compressor cycles on and off as it should but air temperature at outlets is merely colder as outside temp.
Every time the system activated the compressor the engine RPM drop significantly, at a point the engine even stopped. So the compressor runs very sluggish.

I checked the refrigerant hoses:
- hight pressure line is hot at the compressor
- Low pressure line is NOT cool after condenser (as I'd expect it to be)

No error codes in the A/C diagnose function.

Any guess what might wrong? I don't know whether or not the A/C was operative before as European customs require all R12 refrigerant to be drawn and recycled for newly imported cars. So maybe the orifice is stuck?
What can I test now? I'm terribly lost when it comes to A/C stuff...