Refrigerant Recovery, Recycling, Handling, and Regulatory Compliance
The rules are part of the repair
Section 609 of the Clean Air Act requires certification before you service or repair motor vehicle air conditioning, and it prohibits venting refrigerant to the atmosphere. Recovery, recycling, and charging must use approved equipment: recover into a DOT-approved recovery cylinder, never fill it above 80 percent by weight, and use separate machines, hoses, and fittings for R-134a, R-1234yf, and any other refrigerant. Identify the refrigerant before recovery. Mixing refrigerants turns the cylinder into hazardous waste and contaminates your machine.
R-1234yf is mildly flammable (A2L), uses different service fittings and oil, and requires equipment built to the appropriate SAE standards. Other compliance items: disposable refrigerant cylinders may not be refilled; shipping cylinders requires proper labeling and paperwork; unapproved substitutes such as propane blends, R-22, or hydrocarbon mixes must never be used; retrofitting to a different refrigerant requires approved procedures and a new label.
Traps
A question that describes topping off a leaking system without repair; treating a small venting as harmless; using one machine for both refrigerants; assuming certification is only needed to buy refrigerant; or believing the system must be evacuated before recovery.
Rule of thumb: recover, then recycle or clean, then evacuate (typically 15 minutes or more to about 500 microns, holding vacuum to prove no leaks), then charge by weight. Never charge by gauge feel alone.