Abstract: A cylinder is provided with a piston therein having a piston rod screw threadably engaging through one end cap so that rotation of the rod moves the piston along the cylinder. A filler is situated in the other end cap thus allowing the cylinder to be filled with refrigerant oil. An injection assembly is connected to the other end cap and includes a valve, a tube and a connector which may be connected to the high or low side of the refrigerant circuit of a refrigeration assembly such as an air conditioner. Once connected to the refrigerant circuit, a loosening of one union allows the refrigerant within the circuit to purge the line whereupon the union is tightened. The piston rod is marked with indicia along the length thereof so that rotation of the rod a predetermined distance indicates to the operator that a given amount of oil has been ejected from the cylinder and into the refrigerant system.