Three old R-22 window units, an unlabelled cylinder and a tight budget
A technician visits a government school in Cuttack that runs three 1.5 TR window air conditioners, all about nine years old and all on R-22. Unit 1 has a leaking flare at the suction valve with clear oil staining; units 2 and 3 still cool but have never been serviced and the school has no refrigerant stock or service records. In the workshop there is a grey unlabelled cylinder left behind by a former technician, and a helper says it holds 'R-22 mixed with some 410' recovered from scrapped units and can be used to top up unit 1. The headmaster wants the cheapest possible repair before an inspection in three days and asks whether the old units can simply be 'converted to the new gas' instead of being replaced.
1. Can the unlabelled cylinder be used to top up unit 1? Justify your answer.
Read the worked answer
No. An unlabelled cylinder is unidentified refrigerant, and that alone disqualifies it.
The likely contents are a mixture of R-22 and R-410A recovered from different units. R-22 is a single-component HCFC that uses mineral oil; R-410A is a near-azeotropic HFC blend that uses POE oil and runs at roughly 60 per cent higher pressure. A mixture has an unknown composition and an unknown temperature glide, so the saturation pressure on the gauge no longer tells you the evaporating temperature, and the correct superheat cannot be set. Fractionation during charging can make the composition drift further.
Practically, the risks are wrong pressures, oil sludge and poor oil return, blocked capillary or expansion valve, high discharge temperature, and premature compressor failure - a far bigger cost than a new charge. There is also the environmental and legal point: refrigerant must not be vented, and unidentified gas cannot be legitimately reclaimed, so the cylinder must be labelled as waste and sent to a certified reclaimer, not used in a customer's equipment. The honest answer to the headmaster is that the cylinder saves nothing; it converts a small repair into a compressor replacement.
2. Describe the correct repair and charging procedure for unit 1.
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- Isolate power, remove the unit from the window sleeve if needed, and fit gauges. Recover the remaining charge into a clean, evacuated, weighed recovery cylinder; do not blow it off to atmosphere. Note the recovered weight.
- Repair or renew the leaking flare: cut back if the cone is damaged, re-flare with a proper flaring tool, keep the cone square and burr-free, and tighten to the specified torque with a torque wrench rather than by feel.
- Pressure test with dry nitrogen, typically at the manufacturer's test pressure (for an R-22 window unit about 15 to 20 bar is adequate and safe for the low side), and hold it. A 24-hour stand with temperature correction is best; a shorter hold is acceptable only if the gauge shows no fall after the gas has cooled to ambient.
- Leak-test all joints with soap solution or an electronic detector, not with refrigerant.
- Triple evacuate to below 500 microns (66 Pa), holding for at least 10 minutes with no rise above about 1000 microns, which confirms no leak and no moisture.
- Charge by weight to the nameplate quantity, run for 20 to 30 minutes, then verify superheat (about 5 to 8 K at the suction service valve for a capillary system) and record the final charge on a label and in the school's register.
3. Give the headmaster a reasoned recommendation: repair, retrofit or replace.
Read the worked answer
Repair first, replace in a planned way, and never retrofit these units.
Retrofit is the weakest option. The R-22 compressor, capillary and mineral oil are matched to R-22; substituting R-410A or R-32 would need higher-pressure components and a POE oil change, which no manufacturer supports for these models. Hydrocarbon refrigerants are A3 flammable and must not be charged into a unit not designed and marked for them.
Repair unit 1 now: a flare repair plus a weighed R-22 charge is a same-day job and keeps the school running through the inspection. But R-22 is an HCFC with an ozone depletion potential of about 0.055 and a global warming potential above 1800, and supply for servicing is shrinking under India's HCFC phase-out plan, so the cost per kilogramme will keep rising and availability will fall.
Advise the headmaster to budget for replacement of all three over two financial years with R-32 inverter units: R-32 has zero ODP and a GWP of about 675, and an inverter unit typically draws well under two-thirds of the old unit's power. Keeping the repaired unit as a standby after the first replacement keeps the school cool during changeover. Put the recommendation and the phased cost in writing so the decision is documented.