dont fight it replace it with R134A. like mentioned above do a test on the system and find out first what casued your loss of cooling. Can be seal on the compressor, o rings. Condensor or evaporator. Evacuate the system and flush the system. Remove the old reciever / drier and replace it. Install the adapter valves. Perform the vaccum and recharge with r134A. Who ever tells you other wise just wants your money. I have done it many times. 40 Degrees at the central vent, windows open test. Regarding the condensor comment if you can find one replace it. but i have done it both ways and no issues so far. Most of the times leaks show up after a long time are compressor seals or bad schraeder valves. tell tales signs are compressor oil near the potential problem area. hope this helps.
