A service port fitting tells you what a vehicle was designed for. It doesn't tell you what's actually inside. That gap is where most expensive R-1234yf mistakes start, and it's fixable with proper refrigerant identification before recovery, every time. 

This breaks down the real causes behind common errors: skipped pre-charge leak detection, sampling issues and oxygen sensor degradation that mimics contamination. It also clears up the R-1234yf vs R-134a myths still floating around shops — including the top-off question that costs techs the most comebacks. 

No guesswork. Just what's actually causing the lockouts, and how to fix it fast. Watch the full Tech Tip Short to get the specific fixes, not just the warning.