The Mastercool 53123-YF Refillable R1234yf Oil Injector injects oil or dye to air conditioning systems. To inject oil, users can connect the injector to the low side of the A/C system and twist the handle until you reach the desired amount. The injector hose comes complete with a R1234yf low side coupler with an extended disconnect sleeve that meets SAEJ639 and J2888 standards. This unit also features a nylon barrier blue hose that meets J2888, EPA, SAE and UL standards.