When servicing certain appliances such as domestic refrigerators, window units, package units, ice machines, and automotive air conditioning, there cannot be any guess work as to how much refrigerant should be in the unit. There is a specific amount of refrigerant used in this type of equipment, and the manufacturer places that amount on the data plate. The amount needed in these units is usually given in pounds and ounces. When using small quantities such as this, one of the ways that it could be handled is with a very fine tuned scale or the charging cylinder. The cylinder is a valuable tool that should be a part of your tool inventory if you work on this type of equipment.
The operation of the charging cylinder is extremely easy once you understand the procedure. A tube where you place the amount of refrigerant is located in the center of the cylinder. On the outer perimeter is a plastic, movable, outer cylinder. At the top of the inner tube a valve and pressure gauge are located; and at the bottom there is a valve. Place a small amount of the refrigerant to be used into the cylinder through the lower valve. This small amount of liquid places pressure on the cylinder. A charging cylinder provides refrigerant in liquid form.
Read the amount of pressure on the gauge, rotate the outer cylinder until the proper refrigerant and pressure line up with the index. This outer, plastic, cylinder has graduations marked on it. These graduations are in ounces. Open the lower valve and allow liquid refrigerant to enter the inner tube, carefully observe the increments as the liquid column fills the center tube. When the proper amount of ounces is reached, close the lower valve. The exact amount of refrigerant needed to charge the specific system is enclosed in the center tube of the charging cylinder. Liquid refrigerant is dispensed from a refrigerant drum with the use of a valve labeled “liquid,” or by turning the drum upside down. Always allow a couple of ounces of refrigerant to purge your charging hose. Never break the vacuum of a good evacuation until the charging hose is purged of air and full of refrigerant.