Decommissioning Day: Three Refrigerants, One Recovery Cylinder
A workshop schedules a decommissioning day. The job list: two R-22 window units (nameplate charge 0.75 kg each), one R-410A split-type (nameplate 1.40 kg), and an unlabelled cylinder left behind by a previous owner. Available equipment: one recovery machine marked for HFCs, one 12.3 L recovery cylinder (tare 8.4 kg, working pressure 400 psig) that already holds about 1.5 kg of R-22, one manifold gauge set, one scale, and no reclaim service within 200 km. The technician's plan is to pull all three units into the same cylinder to save time, write "MIXED" on it with a marker, and hand it to the scrap buyer. For the R-410A unit he intends to run the recovery machine until the gauge reads 0 psig, then open the flare to atmosphere and cut the line set out. Liquid densities at 25 °C: R-22 1.19 kg/L, R-410A 1.06 kg/L.
1. Calculate the maximum refrigerant weight the cylinder may hold under the 80% fill rule, and determine whether the planned job would fit.
Read the worked answer
Water capacity 12.3 L; 80% fill limit = 12.3 × 0.80 = 9.84 L of liquid.
R-22: 9.84 L × 1.19 kg/L ≈ 11.7 kg maximum refrigerant weight in the cylinder. It already holds 1.5 kg, so there is about 10.2 kg of headroom; the two window units add 1.5 kg, bringing it to 3.0 kg - comfortably inside the limit.
R-410A: 9.84 L × 1.06 kg/L ≈ 10.4 kg; 1.5 kg existing plus 1.4 kg would be 2.9 kg - also inside.
So capacity is not the reason to refuse the plan; segregation is. Two further points: fill must be controlled by weight on a scale, never by watching the gauge or a sight glass, because the cylinder can become liquid-full before the pressure looks alarming; and the cylinder should stay out of direct sun, since R-410A pressure rises steeply with temperature and the 80% rule is what keeps it safe.
2. Give at least three technical reasons why R-410A must not share a cylinder with R-22, and explain the consequences of mixing.
Read the worked answer
- It cannot be un-mixed. R-410A is a 50/50 blend of R-32 and R-125. Once blended with R-22 or an unknown gas there is no separation back to specification, so no reclaimer will accept it as product - the whole cylinder becomes destruction-only waste and is charged as hazardous waste.
- Oil chemistry. The R-22 units carry mineral oil; the R-410A unit carries POE, which is hygroscopic. Cross-contamination carries moisture and acid into a system that was clean, and a recovery machine used on mineral oil must be purged before it touches a POE system.
- Equipment and cylinder ratings. Hoses and the machine retain residual refrigerant; a machine run on R-22 should not go straight onto R-410A without a nitrogen purge. The cylinder's pressure rating and the refrigerant's expected storage temperature must also be checked.
- Records. A cylinder must be marked with the refrigerant identity, the date and the gross weight. "MIXED" in marker is not a record and cannot be traced back to any unit.
Use one cylinder per refrigerant, label each, and weigh before and after.
3. What is the correct recovery endpoint for the R-410A unit, and how should the unlabelled cylinder and the paperwork be handled?
Read the worked answer
0 psig is atmospheric pressure, not empty - the system still holds refrigerant vapour, and cracking the flare vents it to the room. The endpoint is a vacuum: pull each unit down to 500 microns (about −29.9 inHg) and hold, or to roughly 10 inHg vacuum where the machine cannot go deeper, then close the valves, cap the stubs and only then cut. Never use the system compressor as a recovery device; it is not designed to pump to vacuum and will overheat.
The unlabelled cylinder: do not add it to anything, do not crack the valve to "sniff" it, and do not guess the contents from pressure alone. Mark it "UNKNOWN - DO NOT USE", store it upright and segregated, and route it to identification or disposal through the proper hazardous-waste channel.
Paperwork: record recovered mass per unit, cylinder gross weight before and after, the destination of each refrigerant, the date and the technician's name - that record is what proves the job was done lawfully and is what the scrap buyer should be signing for.