I had some more R134a added to my car recently. The mechanic said when he had his shop, he would have completely evacuated the system to measure how many ounces of refrigerant were still in the system. He also said the old R12 systems were less leaky than R134a. R12 was phased out because of the ozone layer.

I think refrigerator and AC repair companies are required to capture and recycle the refrigerant - they don’t seem to have the equipment to capture and measure refrigerant like auto mechanics.

R22 (phased out refrigerant for home AC) has chlorine in it, while R134a doesn’t have chlorine, making it easier on the ozone layer. R134a is being replaced with R1234yf.

The best refrigerant is CO2, but this has the greatest tendency to leak.