Conflicting Information About a Retrofitted System's Refrigerant
A facilities manager provides a service history for a 20 kW packaged rooftop unit. The nameplate says R-22. The service history shows a 2019 entry 'converted to R-407C', a 2021 entry 'topped up with R-22', and a 2023 entry with no refrigerant named but a note 'pressure low, added 2 kg'. The current technician is asked to quote for a repair. The unit is on a roof, the only access is a ladder, and the facilities manager wants the quote today. The technician has a recovery cylinder labelled R-407C and another labelled R-22, neither dedicated to mixed refrigerant. The system is running and the suction line is frosted.
1. What can the technician conclude about the refrigerant in the system, and what are the implications?
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The technician cannot conclude that the system holds R-407C or R-22. The records are contradictory: a conversion to R-407C in 2019 followed by an R-22 top-up in 2021 means the charge is almost certainly a mixture, and the unnamed 2023 addition makes it worse. R-407C is a zeotropic blend, and mixing it with R-22 changes composition and performance unpredictably. The frosted suction line suggests low charge, restriction or another fault, but it does not identify the refrigerant. The implication is that the existing charge must be treated as unknown/mixed, recovered into a cylinder dedicated to that purpose and not reused, and the system must not be topped up with either R-22 or R-407C. The technician should explain to the facilities manager that the records are unreliable and that a proper recover, leak test and retrofit or replacement decision is needed.
2. The facilities manager wants a quote today. Outline what the technician can quote and what must be flagged as provisional.
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The technician can quote confidently for the recover of the unknown charge, a leak test with OFN, and the labour and access for the roof work. The refrigerant and recharge cost should be flagged as provisional because the final refrigerant choice depends on the leak test and on whether the system is retrofitted to a compatible refrigerant or replaced. If a retrofit is chosen, the quote should include new filter-driers, any elastomer or oil changes recommended by the refrigerant supplier, evacuation and a full charge. The technician should also note that if the leak is in an inaccessible part of the packaged unit, replacement may be more economical. Quoting today is possible if the quote is clearly staged and the assumptions are written down. The technician should not quote a simple top-up, because the mixed charge makes that non-compliant and technically unsound.
3. What information should the technician record and pass on, and how should the cylinders be managed?
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The technician should record the nameplate refrigerant, the contradictory service entries, the measured pressures and temperatures, the frosted suction line observation, and the decision to treat the charge as mixed. The recovered charge should go into a cylinder labelled with the date, the unit, and 'mixed/unknown - do not reuse', with the weight recorded. Neither the R-407C nor the R-22 cylinder should receive the mixed charge, because that would contaminate a cylinder intended for identifiable refrigerant. A dedicated mixed-refrigerant cylinder should be used, or one of the existing cylinders permanently redesignated and relabelled. The technician should pass the record to the facilities manager and keep a copy, and should recommend that future service entries always name the refrigerant and the amount. Clear records prevent the next technician facing the same confusion.