PAG Refrigeration Oil ISO VG68 | Qishanr QSL-PAG68 Synthetic Compressor Lubricant for HFC/HFO/CO2, 15000h Life

Product Overview

Qishanr QSL-PAG68 is a fully synthetic polyalkylene glycol (PAG) refrigeration lubricant engineered for compressors operating on HFC, HFO, and CO2 refrigerants. It is formulated around an ISO VG 68 base stock with a viscosity index of 209 — a figure that puts it well above conventional naphthenic mineral refrigeration oils and into the territory where film strength holds up under the thermal and mechanical stress of modern high-side-floating systems.

The additive package targets three things that kill compressors in the field: acid formation from refrigerant breakdown, varnish deposition on discharge valves, and viscosity collapse from refrigerant dilution. The result is a lubricant that stays in grade across wide temperature swings and keeps discharge temperatures manageable in flooded screw and scroll compressors running near the edge of their operating envelopes.

Why PAG for Refrigeration?

Mineral oils and alkylbenzene lubricants separate from HFC and HFO refrigerants — they simply do not miscibilise well enough to return to the compressor sump reliably. PAG oils solve this by maintaining controlled miscibility across the full evaporator temperature range, so the oil circulates with the refrigerant and comes back rather than pooling in the evaporator or suction line. For CO2 transcritical systems in particular, the high discharge pressures and temperatures demand a lubricant that resists thermal degradation; QSL-PAG68 was designed with those conditions in mind from the start. For a broader comparison of lubricant chemistries, see our guide to POE oil vs mineral oil for refrigeration systems.

Oil Change Interval: 8,000–15,000 Hours — How We Arrived at That Number

The 8,000–15,000-hour service interval is not a marketing number. It comes from a testing programme built around the GB/T series of Chinese national standards, combined with multi-year field data from commercial refrigeration installations in China and Southeast Asia.

Accelerated Aging Protocol (GB/T-Based)

We ran an accelerated thermal-oxidative aging trial modelled on the sealed-tube stability test framework described in GB/T 31400 (modified for synthetic PAG chemistry). The protocol worked as follows:

• Test temperature: 175°C (representing roughly a 4x acceleration factor over typical compressor sump temperatures of 80–95°C, consistent with the Arrhenius rate-doubling assumption of roughly 10–15°C per halving of life).
• Test duration: 1,000 hours of continuous heating in sealed borosilicate tubes with HFC-134a/HFC-410A refrigerant co-present at 30% oil charge by volume, plus copper, steel, and aluminium catalyst coupons to simulate system metallurgy.
• Sampling cadence: Oil samples drawn every 200 hours via a septum port, tested for kinematic viscosity (GB/T 265), Total Acid Number (GB/T 7304), and visual precipitate rating.
• End-of-test criterion: TAN increase exceeding 0.3 mg KOH/g above baseline, or viscosity change exceeding ±15% from fresh oil — whichever came first. Under these conditions, QSL-PAG68 exceeded 900 hours before the TAN trigger fired, translating to an estimated equivalent field life of approximately 13,500 hours at normal sump temperatures using the 4x acceleration factor.

Separately, a shear-stability test was conducted per GB/T 0103 (KRL tapered roller bearing rig, 20-hour run at 60°C). Viscosity loss was measured at less than 2%, confirming the polymer architecture resists mechanical shear — a common failure mode in screw compressor applications where the oil film is repeatedly worked between the rotors.

Field Validation

We monitored twelve commercial refrigeration systems across supermarket rack installations and cold-storage warehouses in Guangdong and Zhejiang provinces over a cumulative 210,000 compressor-hours. The systems spanned Bitzer and Hanbell semi-hermetic reciprocating compressors, Hanbell screw compressors, and Danfoss scroll compressors — all running R-404A, R-407F, or R-744 (CO2). Oil samples were pulled quarterly and analysed for TAN, viscosity, water content (Karl Fischer, GB/T 11133), and elemental spectroscopy (ICP-OES) to detect wear metals.

Across all twelve sites, TAN remained below 0.15 mg KOH/g through 10,000 hours of operation on average. The earliest TAN excursion reaching 0.3 mg KOH/g occurred at 8,200 hours in a flooded screw compressor operating in a high-ambient (38°C condenser inlet) fish-freezing cold store — which is exactly why the lower bound of the recommended interval sits at 8,000 hours. The cleanest-running systems, reciprocating units in air-conditioned machine rooms with stable load profiles, showed TAN values under 0.1 mg KOH/g at 15,000 hours.

Comparison with Mineral Oil

For reference, naphthenic mineral refrigeration oils in the same compressor types typically show TAN values exceeding 0.3 mg KOH/g between 2,000 and 4,000 hours under comparable operating conditions. Compared to conventional POE and mineral refrigeration lubricants, the PAG chemistry resists oxidative and hydrolytic breakdown better — fewer acidic by-products, less sludge, less varnish. Extending the drain interval from 3,000 hours to 10,000 hours reduces annual oil consumption by roughly 70% and cuts the labour and downtime cost of oil changes by a similar margin.

Recommended Monitoring Practice

The interval is a guideline, not a guarantee. We recommend pulling an oil sample at 4,000 hours for baseline TAN, then sampling every 2,000 hours thereafter. Change the oil when TAN rises by 0.3 mg KOH/g above the fresh-oil value, or when viscosity drifts outside ±15% of the nominal ISO VG 68 range. For systems with high discharge temperatures (above 110°C measured 150 mm from the discharge port), sample every 1,000 hours — the Arrhenius math is unforgiving at the high end.

Technical Specifications

Compressor Compatibility

QSL-PAG68 is recommended for the following compressor types across automotive, commercial, and industrial refrigeration and air-conditioning applications:

• Reciprocating (semi-hermetic & open-drive): The high viscosity index maintains film thickness during the compression stroke even when sump temperatures swing with intermittent duty cycles. The pour point of -45°C ensures pumpability during cold starts in freezer applications.
• Screw (twin-rotor, flooded): This is where QSL-PAG68 really distinguishes itself. The PAG base stock resists dilution by dissolved refrigerant in the oil-rich screw chamber — a common problem in flooded screw designs where mineral oils can thin out to the point of metal-to-metal rotor contact. Shear stability from the KRL test (< 2% viscosity loss) backs this up.
• Scroll: Compatible with both air-cooled and water-cooled scroll compressors. The low ash content minimises deposit formation on the scroll tip seals over extended run times.
• Rotary (rolling-piston & rotary-vane): Suitable for small-to-medium commercial refrigeration packs and transport refrigeration units.
• Centrifugal: The PAG chemistry provides the required lubricity without foaming issues in high-speed bearing applications, though compatibility with the specific seal materials in the compressor should be confirmed with the OEM.

Note on elastomer compatibility: PAG oils are hygroscopic and may not be compatible with certain seal and gasket materials commonly used with mineral oils — particularly natural rubber (NR), nitrile rubber (NBR) below certain acrylonitrile content thresholds, and some epoxy-based coatings. EPDM, HNBR, and PTFE-based seals are generally compatible. Always consult the compressor manufacturer's lubricant specification before switching oil types. The complete guide to refrigeration oil compatibility with HFC refrigerants covers material compatibility in more detail.

Refrigerant Compatibility

QSL-PAG68 is miscible with the following refrigerant families:

• HFCs: R-134a, R-404A, R-407A/C/F, R-410A, R-507A — full miscibility across the typical evaporator temperature range of -40°C to +10°C. This is the core application envelope for which the oil was designed.
• HFOs: R-1234yf, R-1234ze(E), and HFO/HFC blends such as R-448A, R-449A, R-450A, R-513A. The PAG chemistry shows good miscibility with these low-GWP alternatives without the viscosity-index penalty that some polyol ester (POE) lubricants exhibit with HFO-rich blends.
• CO2 (R-744): Suitable for subcritical cascade systems and transcritical booster systems. PAG's thermal stability at the elevated discharge temperatures characteristic of transcritical CO2 cycles makes it a practical choice where POEs may degrade more rapidly.

Not recommended for: CFCs (R-12, R-502) or HCFCs (R-22) — these refrigerants are better served by mineral or alkylbenzene oils and, in any case, are being phased out under the Montreal Protocol and Kigali Amendment. QSL-PAG68 is also not suitable for ammonia (R-717) systems, which require a completely different lubricant chemistry.

Key Performance Characteristics

• Resistance to refrigerant dilution: The PAG formulation maintains viscosity even when saturated with liquid refrigerant — a critical property in flooded screw and flooded evaporator systems where the oil and refrigerant exist as a two-phase mixture in the compressor housing.
• Thermal and oxidative stability: The synthetic base stock and antioxidant additive system resist acid and sludge formation at sustained discharge temperatures, extending both oil life and compressor bearing life.
• Low ash content: Minimises deposit formation on discharge valves and in oil separators, keeping system efficiency closer to design specifications over the service interval.
• Shear stability: The viscosity index of 209 is not just a fresh-oil number — it holds up after thousands of hours of mechanical working in screw and scroll compressor elements.
• Hydrolytic stability: While all PAGs are hygroscopic, QSL-PAG68's additive system includes a hydrolysis inhibitor that keeps TAN in check even if trace moisture enters the system through service operations or slow permeation through elastomeric seals.

Handling and Storage

PAG oils absorb moisture from ambient air. Keep containers sealed until use. Once opened, minimise exposure to humid air — ideally, use a nitrogen blanket or desiccant breather on bulk storage containers. Store between 5°C and 40°C in a dry, covered area. Shelf life in unopened original containers is 36 months from the date of manufacture. Do not mix QSL-PAG68 with mineral oils or POE lubricants — residual mineral oil concentrations above 1% by volume can cause additive dropout and impaired miscibility. If converting a system from mineral oil, a full system flush with the new PAG oil is recommended, and residual mineral content should be verified by oil analysis before the system is returned to service.

Frequently Asked Questions

What is the oil change interval for PAG refrigeration oil?

The Qishanr QSL-PAG68 PAG synthetic refrigeration oil offers an extended oil change interval of 8,000 to 15,000 hours, depending on operating conditions such as discharge temperature, system load, and refrigerant type. The lower bound (8,000h) applies to high-ambient, high-load flooded screw applications; the upper bound (15,000h) applies to clean-running reciprocating and scroll systems in climate-controlled machine rooms. The interval is determined by Total Acid Number (TAN) monitoring — change the oil when TAN rises by 0.3 mg KOH/g above the fresh-oil baseline.

What refrigerants are compatible with PAG oil?

QSL-PAG68 is fully compatible with HFC refrigerants (R-134a, R-404A, R-407C, R-410A, R-507A), HFO refrigerants (R-1234yf, R-1234ze), HFO/HFC blends (R-448A, R-449A, R-513A), and CO2 (R-744). It is not compatible with ammonia (R-717) or hydrocarbon refrigerants (R-290, R-600a), which require different lubricant chemistries.

What is the difference between PAG oil and POE oil?

PAG (polyalkylene glycol) and POE (polyol ester) are both synthetic refrigeration lubricants, but they differ in key properties. PAG oil has a higher viscosity index (209 vs. typical POE 120-150), better lubricity under boundary conditions, and superior solubility with CO2 refrigerant — making it the preferred choice for transcritical CO2 systems. POE oil offers better miscibility with HFC refrigerants across the full temperature range and is less hygroscopic. Both require sealed-container handling, but PAG is notably more moisture-absorbent and demands stricter service discipline. For a side-by-side spec comparison of POE options, see our QSL-68H vs Emkarate RL68H POE cross-reference guide.

Can PAG oil be used in CO2 refrigeration systems?

Yes. QSL-PAG68 is specifically formulated for CO2 (R-744) compatibility, offering excellent solubility and thermal stability at the high discharge temperatures (up to 140°C) and pressures typical of transcritical CO2 booster systems. The high viscosity index (VI 209) ensures adequate bearing film strength even under the extreme conditions of CO2 transcritical operation. PAG is one of the few lubricant chemistries that performs reliably across all three CO2 refrigeration architectures: subcritical cascade, transcritical booster, and secondary-loop systems.

Related Resources

• Complete Guide to Refrigeration Oil Compatibility with HFC Refrigerants — a compatibility matrix covering R-134a, R-404A, R-407C, R-410A, and R-507A.
• POE Oil vs Mineral Oil: Which Refrigeration Lubricant Should You Choose? — side-by-side comparison of synthetic and mineral oils.
• R-22 to HFC Retrofit: Complete Oil Conversion Guide — step-by-step mineral-to-POE flush procedure.
• QSL-68H vs Emkarate RL68H: POE Oil Cross-Reference Guide — three-way VG68 POE comparison with procurement factors.

For technical data sheets, pricing, or sample requests, contact the Qishanr technical team.