Recovery Cylinder Overfill Risk on a Busy Afternoon
A technician is decommissioning three identical 5 kW split systems in a small office block, all charged with R-410A. Each nameplate states a factory charge of 1.4 kg. The technician has two recovery cylinders: cylinder A is a 12 kg capacity R-410A cylinder last tested two years ago, currently holding 4 kg of R-410A; cylinder B is a 10 kg cylinder with an illegible test stamp. The recovery machine has a high-pressure cut-out that has tripped twice. Ambient is 36 degrees C and the cylinders sit in direct sun on the back of the ute. The technician wants to finish all three systems before lunch.
1. Calculate the available capacity and decide how the recovered refrigerant should be allocated across the cylinders.
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Total refrigerant to recover is 3 x 1.4 kg = 4.2 kg. Cylinder A currently holds 4 kg against a 12 kg capacity, leaving 8 kg of headroom, which is more than enough for 4.2 kg. However, the industry rule is to fill recovery cylinders to no more than about 80 percent of capacity by weight for liquid refrigerants, to leave room for thermal expansion. Eighty percent of 12 kg is 9.6 kg, so the usable headroom is 9.6 minus 4 = 5.6 kg, still sufficient for 4.2 kg. Cylinder B should not be used at all because its test stamp is illegible, so its test status cannot be verified. All 4.2 kg should go into cylinder A, and the technician should record the starting and finishing weights. The high-pressure cut-out tripping suggests the cylinder or machine is overheating, which points to the next issue.
2. Explain why the high-pressure cut-out has tripped and what the technician must change before continuing.
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The cylinders are in direct sun at 36 degrees C ambient, so their internal pressure is high before recovery even starts. As recovered refrigerant enters, the pressure rises further, and the recovery machine's high-pressure cut-out trips to protect the equipment and hoses. The technician must move the cylinders and machine into shade, ideally onto a damp towel or into a water bath to cool them, and allow pressures to stabilise before restarting. Recovery should proceed slowly, with the machine's gauges monitored, and the cylinder should never be filled past its 80 percent limit. If the cut-out continues to trip after cooling, the machine or hoses may be restricted or the cylinder may already be near its limit, in which case recovery must stop and the charge reallocated. Finishing before lunch is not a reason to bypass the cut-out or to overfill.
3. The technician finishes and finds cylinder A now weighs 8.2 kg gross. What checks and records are required before the cylinder leaves site?
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The technician must confirm the net recovered weight by subtracting the cylinder's tare weight, and check that the total remains within the 80 percent limit. If cylinder A's tare is, for example, 6 kg, then the gross of 8.2 kg means 2.2 kg of refrigerant, which is well within limits; the technician should verify the tare stamp rather than assume. The cylinder valve must be closed and capped, the cylinder labelled with the refrigerant type (R-410A), the date and the source, and the cylinder must be secured upright for transport. Records should include the cylinder identity and test date, the recovered weight, the systems decommissioned and the destination of the refrigerant. Cylinder B must be removed from service until it can be properly tested and stamped. The technician should also confirm the recovery machine has been purged and the hoses capped to avoid contamination on the next job.