Refrigerant oil types

The five oil families

• MO, mineral oil: refined petroleum oil, the original lubricant for CFC and HCFC systems.
• AB, alkylbenzene: a synthetic hydrocarbon oil, used alone or mixed with mineral oil on HCFCs and their service blends.
• POE, polyolester: a synthetic ester oil, the standard for HFC and HFO stationary systems.
• PVE, polyvinyl ether: a synthetic ether oil used in some HFC compressors, for example Copeland’s PVE-68 (FVC 68D) for specific variable-speed R-410A models.
• PAG, polyalkylene glycol: a synthetic glycol oil, the usual lubricant in automotive R-134a and R-1234yf compressors and in some CO2 and propane compressors.

Ammonia and some propane compressors also use PAO (polyalphaolefin). BITZER lists mineral oil and PAO as standard for ammonia.

Copeland’s bulletin 93-11 is the most useful single reference for stationary compressors: it lists the preferred and alternate oil for every approved refrigerant, by brand name.

Which refrigerants use which oil

From the manufacturer documents behind each profile. Where sources list more than one oil, the compressor’s own specification decides.

Where sources differ on R-454B (Rheem’s manual says R-454B “is only compatible with POE oils”, Carrier lists certain POE and PVE lubricants), go by the compressor in front of you.

Miscibility and oil return

Oil leaves the compressor with the refrigerant and has to come back. How well the oil dissolves in the refrigerant affects that return; Chemours lists lubricant/refrigerant solubility among the factors in lubricant selection. HFCs mix poorly with mineral oil and alkylbenzene: Chemours notes poor miscibility of R-134a with both, and Solstice calls MO and AB immiscible with R-448A.

That is why converting R-22 to an HFC such as R-407C means changing the oil, and why Chemours says even its R-22 service blends that run on the existing mineral oil may need POE added in some complex systems.

Moisture: POE, PVE and PAG need sealed handling

POE pulls water from the air. An unbranded R-454B outdoor unit manual says POE “can easily absorb moisture from the atmosphere”, tells installers to keep the system sealed as much as possible, and says that if the system is open to the atmosphere for more than 4 hours the compressor oil must be changed. It also says not to break a vacuum with air and to always replace the filter drier when the system is opened for component replacement.

Rheem’s R-454B instructions add that vacuum pumps will not remove moisture from POE oil, that the filter drier only has adequate moisture capacity if the system is properly evacuated, and that the desiccant must be compatible with POE and R-454B. Copeland’s 93-11 bulletin warns that POE needs gloves and eye protection and must not contact materials it can harm, including certain polymers such as PVC/CPVC and polycarbonate.

BITZER describes PAG as strongly hygroscopic in its ammonia lubricant guidance. For PVE, follow the compressor maker’s handling instructions; Oxbox’s R-410A manual requires gauge sets, hoses, containers and recovery equipment designed to handle POE or PVE oils.

Practical handling that follows from these sources:

• Keep oil containers and system openings capped until the moment you use them.
• Do not leave a system open longer than you must. Plug or cap tubing during the job.
• Evacuate properly; see evacuation and microns.
• Replace the filter drier when the system has been opened, using one approved for the refrigerant and oil.

Retrofit oil changes: R-22 to HFC blends

The oil decision depends on the replacement refrigerant. From the manufacturers’ retrofit literature:

• R-407C: Arkema’s Forane 407C page calls for a complete oil change to POE when converting an R-22 system. The Chemours MO99/NU-22B guidelines note that R-22 retrofits to refrigerants such as R-407C require multiple oil changes.
• R-438A (MO99) and R-422B (NU-22B): Chemours says they work with the existing mineral oil or alkylbenzene in most systems. If oil level falls or swings widely, add POE at about 20% of the total oil charge, then small increments until the level is normal, and keep the level below mid-sight glass right after adding.
• R-427A: Arkema recommends replacing MO/AB with POE, usually with one oil change. BITZER tolerates up to 15% residual MO/AB.
• R-448A: the Solstice N40 brochure says about 5% residual mineral oil means a single oil change may suffice on an R-22 retrofit.
• R-449A: Chemours recommends an oil change to POE and new seals on R-22 retrofits.
• R-401A (an R-12 service blend): Chemours says one oil change removes 50–80% of the mineral oil.
• R-507A replacing R-502: Arkema says to reduce residual mineral oil to 5% or less.

After any retrofit, Chemours tells you to label the system with the refrigerant and the oil(s) in it. R-410A is not a retrofit refrigerant for R-22 systems, and Copeland states that A2L refrigerants must not be retrofitted into non-A2L compressors or products. See R-22 replacement options.

Automotive PAG vs stationary POE

R-134a is the clearest example of one refrigerant with two oils. Stationary R-134a compressors run on POE (Copeland POE-32). In vehicles, Chemours’ mobile AC literature gives PAG of 60–135 cSt and says almost all mobile OEMs selected PAGs.

For R-1234yf, Chemours says it is compatible with POE and with PAGs formulated specifically for R-1234yf, and to use the oil the compressor manufacturer designates. Electric (high-voltage) vehicle AC compressors use a dielectric POE; I-CAR, a secondary source, says as little as 1% standard PAG degrades the insulation. Do not carry automotive PAG habits into stationary systems, or stationary POE into a vehicle, without the compressor maker’s approval. See R-134a vs R-1234yf.

Misconceptions to correct

• “Mineral oil is mostly used in residential AC.” That was true in the R-22 era. Residential systems built for R-410A, R-454B and R-32 use POE, with PVE in some compressors.
• “Never use PAG with R-134a.” Wrong for automotive. PAG is the normal lubricant in R-134a vehicle systems; POE is the stationary choice.
• “Any POE will do.” Copeland lists specific viscosity grades (POE-32, POE-46, POE-68) and approved brands per refrigerant and compressor. Match the grade on the compressor or in the bulletin.
• “The vacuum pump will dry wet oil.” Rheem says vacuum pumps will not remove moisture from POE oil, and the OEM manual above answers long exposure with an oil change, not more pumping.