Measuring Refrigerant Charge by Weight
Both liquid and vapor refrigerant can be charged into a system by weight using an accurate charging scale. The amount of refrigerant being weighed into the system may be controlled manually if using a basic scale, or automatically if using an electronic scale. A scale used to charge residential and light commercial systems must be accurate to ±1 ounce. Also, make sure the scale weighing platform mechanism is strong enough to handle the heaviest refrigerant cylinders you intend to use.
Typically, an electronic scale displays the cylinder and/or refrigerant charge weight using a digital readout (Figure SP-4-4)-Programmable models control the flow of refrigerant and can be set to automatically dispense a preset amount of refrigerant and stop flow when the preset amount is reached. Most have a hold function that interrupts charging if the refrigerant cylinder empties before a full system charge is reached. For proper weighing o f the charge, always follow the manufacturer’s operating instructions for the charging scale you use.
Another accurate charging device commonly used to weigh the refrigerant charge into a system is a charging cylinder. Never use bathroom scales or produce scales to weigh a refrigerant charge. They are not accurate enough.
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