Charging cylinders and scales are used to insure that the correct amount of refrigerant is measured into a system when it is being charged. Charging scales are often used when recovering refrigerant from a system in order to determine the exact amount that has been recovered. Use of a particular charging cylinder/scale is determined mainly by the type and size of the system being serviced. Since the operation and efficiency of the refrigeration system depends on having a proper charge, the most important feature to be considered when selecting a charging cylinder/scale is its accuracy.
Graduated charging cylinders (Figure 1-14) are used for charging refrigerant into smaller systems whose charge is stated in ounces or a few pounds and ounces. The charging cylinder has marked graduations and a visible column of liquid refrigerant so that the liquid level can be observed as it drops during charging. On top of -the cylinder is a pressure gauge used to determine, by pressure-temperature relationships, the temperature of the refrigerant in the cylinder. Most cylinders have heaters in the bottom to keep the temperature and pressure of the refrigerant from dropping as refrigerant is being removed from the cylinder. To maintain the accuracy of a system charge, the charging cylinder selected should be large enough to hold the full charge of the system being worked on.
Electronic charging meters (scales) can be used to charge both small and large systems by weight. The scale used must be matched to the system size. For example, a scale used to charge residential and light commercial systems must be accurate to within an ounce. Also, be sure the scale weighing platform mechanism is strong enough to handle the maximum size refrigerant cylinders you intend to use.
Electronic scales (Figure 1-15) and programmable, fully automatic charging scales are available. Depending on the model and its intended use, charging scales are calibrated to weigh refrigerant in pounds, ounces, kilograms, and/or grams with an accuracy of about ±2 percent. Typically, they display the cylinder/refrigerant weight using a five-digit LCD display, sensitive to 1/2-ounce resolution. Programmable models control the flow of refrigerant. They can be set to automatically dispense a preset amount of refrigerant and tum off when the preset amount is reached. Most have a hold function that interrupts charging if the refrigerant cylinder empties before the full system charge is reached.
