equipment service
Charging by Weight (Cylinder Method)
Put a measured amount of refrigerant into a system with the cylinder on a scale.
13 steps5 criticalLimit 15 minAlways tested
Steps
- 1Critical stepLeak test and evacuate the system first so air and moisture are out before you charge it
- 2Confirm the refrigerant the equipment calls for and that the cylinder label matches; use no other refrigerant
- 3Check the cylinder and its valve for damage, and use a manifold and hoses made for the refrigerant and its pressure
- 4Connect the manifold and hoses with the cylinder on an electronic scale; never force a connection
- 5Zero the scale as the scale maker directs
- 6Critical stepFind the charge amount and method in the equipment manufacturer's data: by weight, superheat or subcooling
- 7Critical stepFor a blend such as R-410A, charge liquid: invert a standard cylinder, or use a dip-tube cylinder upright
- 8Where vapor would normally be charged into a running system, put a metering valve in the charging line so the liquid flashes to vapor (Arkema, for R-410A); never let liquid reach the compressor
- 9Critical stepOpen valves slowly and watch the scale and gauges
- 10Stop at the specified weight; do not overcharge
- 11Close the cylinder and manifold valves, then disconnect without venting refrigerant
- 12Run the system and check operating readings against the manufacturer's figures
- 13Record the refrigerant type and amount added where required (for appliances with a full charge of 50 or more pounds of class I or II refrigerant, 40 CFR 82.157, in which case the owner also gets documentation) and under your employer's rules
What graders are watching for
Tips
- For blends, charge liquid, not vapor. A manufacturer notes that taking vapor from the cylinder can change the blend's composition and lower efficiency.
- Weight is not the only measure. Manufacturers set the charge by superheat, subcooling or weight depending on the system and its metering device, so follow the equipment's own manual.
- Exam recall for low-pressure (Type III) recharging: introduce vapor before liquid to prevent freezing of water in the tubes, and charge centrifugals through the evaporator charging valve.
Common mistakes
- Charging a system that was never evacuated or leak tested.
- Using a different refrigerant than the equipment calls for.
- Forgetting to zero the scale, so the weight added is wrong.
- Charging vapor from a blend cylinder, which can shift the blend.
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