Introduction: Older R22 chillers still run on mineral refrigeration oil, and the reason comes down to refrigerant chemistry rather than habit.
Thousands of water-cooled chillers built before the 2010s still sit in hospital basements, food plants, and commercial towers, and most of them are charged with R22. Their maintenance crews keep asking the same practical question: can these machines keep running, and can they keep using the oil that is already inside them? The answer starts with how HCFC-22 behaves with mineral oil in a compressor circuit. Once that pairing makes sense, the rest of the picture falls into place — how heat and load age the oil, why oil condition matters more than the calendar, and where the mineral oil story ends and a different refrigerant chemistry begins.
For decades, mineral refrigeration oil was simply the standard lubricant in R22 equipment. That was not a compromise or a leftover habit: HCFC-22 and naphthenic mineral oil are a matched pair. The refrigerant dissolves a working amount of oil and carries it through the condenser, the expansion device, and the evaporator before returning it to the compressor sump. Larger chillers with screw compressors typically specify ISO VG 100 oil to hold a thick hydrodynamic film across big rotor bearings. QISHANR 5GS is one example of that category: a wax-free naphthenic mineral oil at ISO VG 100, with 100 cSt at 40 °C, a 190 °C flash point, and a -30 °C pour point, listed for R22 along with CFCs, HCFCs, R717, R290, and R600a.
The key word is miscibility. HCFC-22 contains chlorine, which makes it a strong solvent for mineral oil. Because the two mix, the oil that leaves the compressor with the discharge gas does not sit in the piping; it travels with the refrigerant, condenses alongside it, and is drawn back into the crankcase. That continuous circulation is what keeps bearings, rotors, and the shaft seal supplied with lubricant. A wax-free naphthenic base oil supports the same behaviour at low evaporator temperatures, which is why chiller duty in the roughly -20 °C to +5 °C range has traditionally been served by naphthenic mineral oil rather than a paraffinic oil that can throw wax.
R22 is an HCFC, and HCFCs are being phased out under the Montreal Protocol, with service rules in the United States handled through EPA Section 608. In practice, that means the machines already installed are maintained rather than torn out on a fixed date. Technicians repair leaks, recover and recharge refrigerant, and change oil and filters on existing R22 chillers every day, often using reclaimed or stockpiled refrigerant. This is a maintenance reality, not a recommendation to specify R22 in new equipment. For an installed R22 chiller, mineral refrigeration oil remains the correct lubricant family, and it stays the reference point whenever a maintenance team decides what to put back into the sump.
Oil inside a chiller compressor lives under constant thermal and mechanical stress. In water-cooled screw compressors, discharge temperatures commonly sit between 80 °C and 120 °C, while the oil film in the bearings carries rotor loads measured in hundreds of kilograms. Heat, oxygen, metal surfaces, and trace moisture together drive oxidation. Over time the oil darkens, its viscosity drifts away from the ISO VG 100 target, acid numbers climb, and sludge and varnish start forming on hot surfaces. A 190 °C flash point on a mineral chiller oil gives useful headroom above normal discharge temperatures, but it does not stop oxidation from progressing month after month. Load patterns matter just as much as temperature. A chiller that runs at full load all summer and cycles lightly in winter pushes the oil through repeated heating and cooling. Large screw compressor bearings rely on a full hydrodynamic film, and that film thins when viscosity drops or when the oil is diluted by liquid refrigerant carryover. Moisture is the quiet problem: water in oil reduces dielectric strength, encourages corrosion, and can create foam that starves the oil pump. Maintenance teams read these signals from oil colour, smell, sump temperature, and periodic oil analysis rather than from a fixed calendar, which is why oil condition monitoring stays at the centre of R22 chiller upkeep.
The R22 and mineral oil pairing depends entirely on the chemistry of the refrigerant, and that is exactly why it does not carry over to HFCs and HFOs. Refrigerants such as R134a, R410A, R404A, and the newer HFO blends contain no chlorine. Without that chlorine, they will not dissolve mineral oil. The oil goes out with the discharge gas, reaches the evaporator, and stays there. It coats tube surfaces, reduces heat transfer, and does not return to the compressor in the quantity the bearings need. Over time that shows up as rising discharge temperature, falling capacity, and eventually a starved compressor. Polyol ester (POE) and some PVE oils exist for these systems precisely because they mix with HFC and HFO refrigerants and keep the circuit lubricated. That boundary is published on lubricant data sheets, and it matters more than branding. A naphthenic refrigeration oil manufacturer and a POE refrigeration oil manufacturer maintain separate compatibility charts for a good reason: the label decides whether a service van carries the right jug. QISHANR 5GS, for instance, is listed for R22, R717, R290, R600a, CFCs, and HCFCs, and the specification stops there. Distributors who stock wholesale refrigeration oil for legacy R22 machines alongside wholesale POE refrigeration oil for HFC equipment normally keep those lines physically apart, because a mix-up at the point of top-up is a compressor failure rather than an inconvenience.
R22 chillers keep using mineral refrigeration oil because HCFC-22 and naphthenic mineral oil work together inside the circuit: the refrigerant picks the oil up and brings it home. Maintenance on those machines is a live activity under HCFC phaseout rules, not a new-system recommendation. Heat, load, and moisture decide how long the oil lasts, so condition monitoring and the correct viscosity grade matter more than any fixed interval. As soon as the refrigerant changes to an HFC or HFO, the lubricant chemistry has to change with it. Technicians and buyers can review the QISHANR 5GS listing for its listed refrigerant compatibility and ISO VG 100 data before making maintenance decisions.
A: Because HCFC-22 and naphthenic mineral oil are miscible. The refrigerant dissolves the oil, carries it through the condenser and evaporator, and returns it to the compressor sump, which keeps bearings and rotors lubricated. That circulation is why mineral oil has been the standard lubricant in R22 chillers for decades and still works in installed equipment today.
A: The oil stops circulating. HFC and HFO refrigerants contain no chlorine, so they cannot dissolve mineral oil; the oil collects in the evaporator, reduces heat transfer, and starves the compressor of lubricant. Those systems are designed around POE or PVE oil, so putting the wrong lubricant family in is a reliability problem rather than a minor top-up mistake.
A: No. Phaseout rules limit new production of HCFC-22 and shape how service refrigerant is handled, but installed R22 chillers are still repaired, recharged, and re-oiled under those rules, usually with reclaimed or stockpiled refrigerant. Phaseout policy is about new equipment and long-term supply, not about shutting down machines that are already running.
Stationary Refrigeration and Air Conditioning | US EPA
Standards and Guidelines | ASHRAE
Refrigeration Compressor Lubrication | Machinery Lubrication
