Abstract: A plurality of refrigeration units are successively charged with a liquid refrigerant which is dispensed by a positive displacement pump including a hydraulically actuated ram or piston slidably supported within a dispensing cylinder. An elongated tension coil spring extends parallel to the axis of the cylinder, and the piston carries a photosensing device which senses the helical turns of the spring when the piston is actuated to provide corresponding electrical pulses which are counted for precisely controlling the axial movement of the piston and the displacement of the refrigerant into each refrigeration unit. The length of the spring and the uniform spacing or pitch of the helical turns is automatically changed in response to changes in temperature of the refrigerant being dispensed to assure that each refrigeration unit is charged with precisely the desired weight of refrigerant regardless of changes in temperature of the refrigerant.