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How to Use the Refrigerant Oil Miscibility Calculator
Select the refrigerant in the system or going into it, then select the lubricant in the compressor. Six lubricant families are covered: MO, AB, POE, PVE, PAG and PAO.
Leave the scenario on Check a pairing for a new or existing system. Switch to Retrofit when the lubricant is already in a system that is changing refrigerant.
Enter the share of the old oil you expect to drain on each change, and choose a target for the old oil left. The defaults are 70% drained and a 5% target.
Press Check Oil Compatibility to see whether the pairing is suitable, the standard lubricant for the refrigerant, the handling notes and, for a retrofit, the number of oil changes needed.
Refrigerant and compressor oil compatibility
A refrigerant and its compressor oil travel around the circuit together, so the oil has to stay mixed with the refrigerant well enough to return to the compressor. When it does not, oil collects in the evaporator, heat transfer falls and the compressor runs short of lubricant. This calculator checks a refrigerant and lubricant pairing against manufacturer and published data, names the lubricant the refrigerant normally uses, and plans the flush when an R-22 system with mineral oil is converted to an HFC.
Each pairing gets one of four results: suitable, check with the compressor maker, not suitable, or no confirmed data. The last one is deliberate. Where the sources checked do not confirm a pairing, the calculator says so instead of guessing.
The six lubricant families
Mineral oil (MO) and alkylbenzene (AB) are the traditional lubricants for CFC and HCFC refrigerants such as R-22. POE (polyolester), PVE (polyvinyl ether) and PAG (polyalkylene glycol) are polar synthetic oils that mix with HFC and HFO refrigerants. POE is the standard for stationary HFC systems, PAG is common in automotive air conditioning and in some CO2 and propane compressors, and PVE is specified by some scroll compressor makers for R-410A, R-32 and R-454B. PAO (polyalphaolefin) is a synthetic hydrocarbon oil, so like mineral oil it does not mix with HFCs. The international classification of compressor lubricants is ISO 6743-3, which covers air, gas and refrigeration compressors.
Compatibility matrix
The table is the data behind the calculator. A check mark means the lubricant is a standard choice for that refrigerant, a triangle means the answer depends on the compressor maker, a cross means the lubricant is not suitable, and a question mark means the sources checked do not confirm the pairing. The calculator highlights the pairing you select.
| Refrigerant | Mineral | Alkylbenzene | POE | PVE | PAG | PAO |
|---|---|---|---|---|---|---|
| R-22 | ✔ | ✔ | ✔ | ? | ? | ? |
| R-134a | ✖ | ✖ | ✔ | ? | ✔ | ✖ |
| R-404A | ✖ | ✖ | ✔ | ? | △ | ✖ |
| R-507A | ✖ | ✖ | ✔ | ? | △ | ✖ |
| R-407C | ✖ | ✖ | ✔ | ? | △ | ✖ |
| R-410A | ✖ | ✖ | ✔ | ✔ | △ | ✖ |
| R-32 | ✖ | ✖ | ✔ | ✔ | △ | ✖ |
| R-448A | ✖ | ✖ | ✔ | ? | △ | ✖ |
| R-449A | ✖ | ✖ | ✔ | ? | △ | ✖ |
| R-452A | ✖ | ✖ | ✔ | ? | △ | ✖ |
| R-454B | ✖ | ✖ | ✔ | ✔ | △ | ✖ |
| R-513A | ✖ | ✖ | ✔ | ? | △ | ✖ |
| R-450A | ✖ | ✖ | ✔ | ? | △ | ✖ |
| R-1234yf | ✖ | ? | ✔ | ? | ✔ | ? |
| R-422D | △ | △ | ✔ | ? | ? | ? |
| R-290 | ✔ | ✔ | ✔ | ? | ✔ | ✔ |
| R-744 (CO2) | ✖ | ✖ | ✔ | ? | ✔ | ✖ |
Viscosity grade comes from the compressor maker
The ISO VG number comes from ISO 3448. It is the mid-point viscosity in mm²/s (cSt) at 40 °C, with a tolerance of 10%, so ISO VG 32 is about 32 cSt at 40 °C. The calculator does not pick a grade, because the right one depends on the compressor design and not only on the refrigerant. Bitzer's CO2 oils show the spread: 55 cSt at 40 °C for the BSE60K POE, 68 for the BSG68K PAG and 80 for the BSE85K POE. Dissolved refrigerant also thins the oil. Hydrocarbons and R-1234yf, a component of blends such as R-454B, dissolve heavily in oil and thin it, so Bitzer calls for sufficient superheat. Read the grade from the compressor nameplate or the maker's oil list.
Converting R-22 to an HFC: the oil change
R-22 systems run on mineral oil or alkylbenzene, and the HFCs that replace R-22 do not mix with either. Copeland's R-22 changeover bulletin for R-404A and R-507 has the R-22 removed from the compressor, the mineral oil drained and POE added, because mineral oil left behind can log in the evaporator and cost capacity. The bulletin also caps what may be left: no more than 10%, 5% recommended, and 1% to 2% where the evaporator uses enhanced tubes. Two complete changes reach about 10% and three reach about 5%, and Chemours says three or four changes are usually enough for R-407C. Recover the refrigerant first with the refrigerant recovery calculator, and where the oil cannot be changed, an oil separator can help oil return.
The calculator models each change as draining a fixed share of the old oil. What is left after n changes is (1 minus the drained share) to the power n. At the default of 70% drained, one change leaves 30%, two leave 9.0% and three leave 2.7%, so three changes meet a 5% target. A 10% target needs two changes and a 1% target needs four, which leave 0.81%. The 70% figure is a planning assumption chosen to match the manufacturers' two-change and three-change results. It is not a measurement. Oil held in the evaporator and lines is not drained with the compressor, so a measured figure from your own job is better. Run time between changes matters too: Copeland asks for at least 24 hours of operation, and several days on large systems with long piping, while Chemours asks for at least 8 hours and says 48 to 72 hours may be required so the new oil mixes with the old.
Low-GWP and flammable refrigerants
Bitzer specifies its BVC32 oil, a PVE, for Orbit scroll compressors on R-410A, R-32 and R-454B, and warns that its scroll compressors may only run on the original Bitzer oil. PVE and POE are both very hygroscopic. An article by engineers at Bitzer Scroll and Idemitsu Lubricants says the moisture-carrying capacity of PVE is up to four times that of POE, and that as a general rule up to 10% residual POE does not affect the properties of PVE. R-290 dissolves heavily in oil: Bitzer's propane compressors use PAG as the standard charge with PAO as an option, and an oil heater is required. Used oil from R-290 and A2L systems can still hold flammable refrigerant, so store it in a pressure-resistant container under nitrogen and label it flammable. For CO2, POE and PAG are the suitable families, and mineral oil, alkylbenzene and PAO are not. Canada's HFC phase-down is moving equipment from R-410A and R-404A toward these refrigerants, and the HFC phase-down calculator shows the schedule.
Moisture, acid and handling
POE absorbs water faster than mineral oil. Copeland's bulletin says POE absorbs moisture very quickly once the container is opened, calls for a new filter-drier at the changeover, and has the system evacuated to 250 microns. Bitzer sets 200 mg of water per kg of oil as the maximum for used oil and asks for less than 50 ppm in alternative oils. Keep POE and PVE in sealed containers, cap every opening, and use fresh oil from a sealed can. Wet oil can form acid, so test the oil from a failed or retrofitted compressor before you reuse it.
Signs of the wrong oil
Oil that does not mix with the refrigerant shows up as oil logging in the evaporator, lost capacity and a compressor short of oil. Copeland notes that mineral oil can log in the evaporator after a changeover to R-404A or R-507. Check the oil for acid and moisture before you replace the refrigerant charge or the expansion device. If the compressor has already failed, work through the compressor diagnosis calculator before you fit a replacement, because a new compressor on the same oil problem fails the same way.
Frequently Asked Questions
Mineral oil and alkylbenzene are low-polarity hydrocarbon oils. They mix with CFC and HCFC refrigerants such as R-22, which is why they are the traditional lubricants for those systems. HFC refrigerants such as R-410A contain no chlorine and do not mix well enough with them, so the oil separates from the refrigerant and logs in the evaporator. Polar synthetic oils do mix with HFCs: POE is the standard for stationary systems, PVE is specified by some scroll compressor makers for R-410A and R-32, and PAG is common in automotive air conditioning. That is why an R-22 conversion needs the mineral oil removed.
Manufacturer guidance is to drain and refill until the old mineral oil left is about 5% or less. Copeland's R-22 changeover bulletin for R-404A and R-507 expects two complete changes to reach 10% or less and three to reach 5% or less, and Chemours says three or four changes are usually enough for R-407C. Where the evaporator uses enhanced tubes, Copeland asks for 1% to 2%, which takes more changes. With the calculator's default of 70% of the oil drained per change, three changes leave 2.7%, so a 5% target needs 3 changes and a 1% target needs 4.
Mineral oil does not mix with HFC refrigerants, so in an HFC system it counts as contamination and should be flushed down to the limits above. Between POE brands, follow the compressor maker: Copeland warns that other POE lubricants may void the compressor warranty, and Bitzer says its scroll compressors may only run on its original oils. PVE is a special case. An article by engineers at Bitzer Scroll and Idemitsu Lubricants reports that, as a general rule, up to 10% residual POE does not affect the properties of PVE.
R-290 dissolves heavily in oil. Bitzer uses PAG as the standard charge in its propane compressors and offers PAO as an option, and supplier data lists mineral oil, alkylbenzene and POE, so follow the compressor nameplate. For R-744 (CO2), POE and PAG are the suitable families. Bitzer uses POE in its subcritical and transcritical CO2 compressors and PAG in some booster and high-pressure designs. Mineral oil, alkylbenzene and PAO are not suitable for CO2.