Recovery Cylinder Capacity and Occupied-Space Leak Repair
A technician responds to a 5-ton R-410A rooftop heat pump with a nameplate factory charge of 14 lb. The unit is in a commercial building and has a confirmed leak at a flare connection in the ceiling plenum. The technician plans to recover the entire charge into a 50 lb recovery cylinder. The cylinder is marked tare 27 lb, water capacity 47.6 lb, and maximum working pressure 400 psig. Its current gross weight on a scale is 54 lb. The cylinder is DOT 4BA300 and has been evacuated. The plenum has no permanent ventilation, and the building is occupied. The technician has a recovery machine, a digital scale, nitrogen, and a leak detector. Local rules require refrigerant recovery before opening the circuit and prohibit venting.
1. Calculate the cylinder’s maximum allowable gross weight and decide whether the full 14 lb charge can be recovered into it. Show the reasoning.
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Maximum gross weight = tare + 0.80 × water capacity = 27 lb + (0.80 × 47.6 lb) = 27 + 38.08 = 65.08 lb. The cylinder currently weighs 54 lb, so it already contains 54 − 27 = 27 lb of refrigerant. The remaining capacity is 65.08 − 54 = 11.08 lb. The unit charge is 14 lb, so the full charge will not fit. Recovering all 14 lb would put the cylinder at 68 lb gross, about 2.9 lb over the 80% limit.
Use a second evacuated recovery cylinder, or recover part of the charge into this cylinder and switch cylinders while weighing continuously. Do not use the 400 psig working pressure as a fill indicator; the 80% weight limit controls. Also confirm the cylinder’s hydrostatic test date is current before use.
2. Describe the safe recovery sequence, including cylinder handling and occupied-space precautions.
Read the worked answer
Wear gloves and eye protection, ventilate the plenum with a fan if possible, and use a refrigerant detector. Connect the recovery machine and hoses, purge the hoses, and recover liquid first, then vapor. Keep the cylinder on a digital scale and stop at 65 lb gross or when the system reaches 0 psig. Never heat the cylinder with an open flame or exceed its working pressure. If the cylinder reaches its limit, switch to the second cylinder rather than continuing.
Because the building is occupied, barricade the work area and keep occupants away. R-410A is an A1 refrigerant, but it can displace oxygen in a confined plenum, so do not rely on odor. If refrigerant concentration rises, stop, ventilate, and evacuate the area. After recovery, isolate the circuit before opening the flare.
3. Outline the leak repair, evacuation, and recharge steps, including documentation.
Read the worked answer
After recovery, repair the flare with a new nut and the manufacturer’s torque, using a backup wrench. Install a new filter drier, purge with nitrogen during brazing, and pressure-test with dry nitrogen at the manufacturer’s test pressure. Leak-check all joints, then evacuate to 500 microns and perform a decay test. If moisture is suspected, break the vacuum with nitrogen and repeat the evacuation.
Charge by weight using the nameplate charge plus any line-set adjustment. Record the amount recovered, the amount charged, the leak location and repair, and the final evacuation result. Verify the recovery cylinder is not overfilled and is DOT-approved with a current test date. Because the leak was in an occupied building, document that ventilation and area control were used and that no refrigerant was vented.