SAE standards for A/C equipment in North America prohibit the use of onboard oil injection, (meaning oil must be added separately). This is the easiest and most efficient way to add A/C oil separately.
Spotgun™ Jr. R-1234yf HFO Kit
Spotgun™ Jr. R-134a, R-1234yf Kit
Spotgun™ R-134a, R-12 Oil Injection Kit
Spotgun™ R-1234yf Kit