Refrigerant Blend Top-Off Check

Top it off. R-513A (Opteon XP10) is an azeotrope: its maker prints a temperature glide of 0 R. Its maker prints "azeotrope with zero glide"; property table "temperature glide 0 r (0 k)", and an azeotrope leaks at its own composition, so there is nothing to fractionate and the remaining charge stays. Chemours also addresses repeat top-offs in passing, answering a flammability question that presumes the practice: "If you top off Opteon XP40 (R-449A) or XP10 (R-513A) multiple times, will this impact its A1 nonflammable rating?" "No. As part of the ASHRAE Standard 34 listing process for an A1 rating, the refrigerant blend undergoes rigorous fractionation testing, including multiple leak recharge scenarios, in order to ensure that the blend will always maintain a nonflammable A1 rating." Charge it as liquid, and remember the top-off is a refrigerant addition under 40 CFR 84.106(b), so the leak rate is calculated on it.

Glide is the difference between the temperature at which a blend starts to boil (the bubble point) and the temperature at which the last liquid boils away (the dew point) at one pressure. A pure refrigerant and an azeotrope have none; a zeotropic blend's liquid and vapor have different compositions in the two-phase regions of the system, so a leak of vapor alone from a two-phase region takes more of the low-boiling components and leaves the charge richer in the high-boiling one. That is fractionation, and glide is the measure of how much of it is possible. In the single-phase regions it cannot happen at all: "In the single phase regions of a refrigeration system (superheated vapor and subcooled liquid), the composition of a refrigerant mixture is constant and behaves exactly like a single component refrigerant."

Not according to the manufacturer documents that address it, which are Chemours' on R-507A, R-407C, R-449A, and the numbers are theirs; for the other zeotropes here no maker has published a leak-and-recharge statement either way. Chemours modelled the worst case for R-407C, a blend with total glide under 11.5 F: the unit off, 50 percent of the charge lost as vapor from a two-phase region, and recharged, five times over. Relative capacity went 100, 95, 93, 92, 91, 91 percent with efficiency unchanged, and Chemours' summary is that "capacity loss is limited to 9%, as the performance of Freon 407C levels out after four 50% leak/recharges", while a heat-pump experiment held the loss at 4 percent after the second recharge. For R-449A the Chemours FAQ says a 10 percent loss and recharge costs a theoretical 2 percent of capacity and no COP. And a leak from a running machine takes liquid and vapor together, leaving the composition "essentially unchanged". So the honest verdict is: top off with the same blend, charged as liquid, expect at most a small shift, and recover and recharge if the machine does not perform afterward or the charge has been mixed with something else.

Azeotropes, by their makers' own descriptions: R-513A, R-514A, R-515B, R-507A. Zeotropes with a printed glide: R-410A (under 0.5 F), R-404A (under 1.1 F), R-407C (under 11.5 F), R-407A (about 8 R), R-448A (about 10.4 R), R-449A (about 7.6 R), R-450A (about 1.1 R), R-454B (about 2 R), R-452B (about 1.8 R), R-454A (about 9 R), R-454C (about 10.8 R). Chemours prints "can be topped off after leaks" on R-454B, R-454A and R-454C, the last two at 9 to 10.8 R of glide, so glide alone does not forbid a top-off; it sets how much the composition can drift and under which kind of leak.

Because that decides whether the leak took vapor alone from a two-phase region. Chemours, on R-407C: "If there is a Freon 407C leak from an operating unit in a two-phase region where mixing occurs (heat exchangers or expansion device), both the vapor and liquid will leak from the unit. The composition of the refrigerant left in the system will remain essentially unchanged from the original composition." And: "if the unit is not operating and there is a vapor leak from a static two-phase region, the composition of the refrigerant that remains in the unit will change." A leak from a liquid line or the suction line is single-phase and changes nothing. If you do not know, this tool treats the leak as the idle case, which is the one where the shift is possible.

Because the vapor above the liquid in a blend cylinder is not the blend. "As with any other refrigerant blend, when charging equipment with Freon 407C, remove liquid refrigerant from the cylinder to charge the unit." Chemours says the same of R-410A ("To achieve optimum performance, remove as a liquid from the cylinder"), and it applies to every zeotrope here. Liquid goes into the high side or is throttled into the suction line through a metering device; it is never dumped into a running compressor.

Yes. "The owner or operator must calculate the leak rate every time refrigerant is added to an appliance unless the addition is made immediately following a retrofit, installation of a new refrigerant-containing appliance, or qualifies as a seasonal variance." (40 CFR 84.106(b)). Every blend on this page that contains an HFC is covered by the AIM Act leak repair rule at a full charge of 15 lb or more, so the pounds you add to top off are the pounds the leak rate is computed from. The leak-rate calculator link on this page carries the blend, the appliance type, the charge and the pounds, and the calculator's own applicability verdict is shown beside it once the charge is entered.

No. "Can you top off Opteon XP40 (R-449A) with any other refrigerant?" "No, mixing refrigerants is not recommended. If Opteon XP40 (R-449A) were to be topped off with a different refrigerant, the resulting mixture would no longer be Opteon XP40. The pressure-temperature characteristics and performance would be impacted." A mixed charge also cannot be reclaimed, and it is one of the few cases where recovering and recharging with virgin refrigerant is the only honest answer, whatever the glide.