How to Choose Refrigeration Oil: Selection Guide by Compressor Type

Quick Selection Matrix

Choosing the correct refrigeration oil requires matching three critical factors: refrigerant type, compressor design, and operating conditions. This matrix provides immediate guidance based on your system specifications.

Step 1: Select Oil Chemistry Based on Refrigerant

Refrigerant miscibility is non-negotiable. The oil must remain fully miscible with the refrigerant across the entire operating temperature range to ensure proper oil return to the compressor.

HFC Refrigerants Require POE Oil

All hydrofluorocarbon (HFC) refrigerants are immiscible with mineral oil. Using mineral oil in an HFC system results in oil logging in the evaporator, poor heat transfer, and compressor failure from oil starvation within weeks.

HFC refrigerants requiring POE oil:

• R-134a (automotive AC, commercial chillers)
• R-404A, R-507A (low-temperature refrigeration)
• R-407C (air conditioning retrofit)
• R-410A (residential and commercial AC)
• R-448A, R-449A (R-404A replacements)

Polyol ester (POE) oils provide complete miscibility with HFC refrigerants from -40°C to +80°C. The Qishanr QSL series covers all HFC applications with viscosity grades from VG22 to VG220. For detailed comparison, see our POE oil vs mineral oil guide.

R-22 Systems: Mineral Oil or POE

HCFC refrigerant R-22 is miscible with both mineral oil and POE oil. If your system will remain on R-22, mineral oil offers lower cost and is not hygroscopic. If you plan to retrofit to an HFC refrigerant in the future, switching to POE oil now simplifies the conversion. Our R-22 retrofit guide covers the complete conversion process.

Natural Refrigerants Use Mineral Oil

Ammonia (R-717), propane (R-290), and isobutane (R-600a) are fully miscible with naphthenic mineral oils. POE oils are not recommended for ammonia systems due to chemical reactivity. For propane systems, mineral oil is preferred for cost and stability. See our R-290 refrigerant guide for propane-specific requirements.

HFO Refrigerants Require POE Oil

Hydrofluoroolefin (HFO) refrigerants such as R-1234yf and R-1234ze require POE oil with the same miscibility characteristics as HFC refrigerants. The QSL series is compatible with all HFO refrigerants.

Step 2: Match Viscosity to Compressor Type and Load

Viscosity grade determines the oil film thickness at bearing surfaces. Too low, and metal-to-metal contact causes wear. Too high, and oil return from the evaporator becomes unreliable.

Scroll Compressors: VG32 to VG46

Scroll compressors operate with tighter clearances and lower bearing loads compared to screw compressors. Lower viscosity oils (VG32-46) provide adequate lubrication while maintaining good oil return in systems with long refrigerant lines.

Typical applications:

• Residential air conditioning: Qishanr QSL-32H (VG32 POE) for R-410A systems
• Commercial rooftop units: Qishanr QSL-46H (VG46 POE) for R-407C systems
• VRF systems: VG32-46 depending on pipe length and evaporator temperature

Screw Compressors: VG68 to VG100

Screw compressors require higher viscosity oils due to higher bearing loads and the need to seal the rotor clearances. VG68 is the standard for most screw compressor applications. Larger industrial screw compressors may specify VG100 or higher.

Typical applications:

• Cold storage warehouses: Qishanr QSL-68H (VG68 POE) for R-404A systems
• Industrial chillers: Qishanr QSL-100H (VG100 POE) for large capacity units
• Process cooling: VG68-170 depending on compressor size and discharge pressure

For cross-reference with OEM oils, see our QSL-68H equivalents guide.

Reciprocating Compressors: VG32 to VG68

Reciprocating compressor oil viscosity depends on compressor size and operating pressure. Small hermetic compressors typically use VG32. Medium semi-hermetic compressors use VG46. Large open-drive reciprocating compressors may require VG68.

Typical applications:

• Display cases and reach-in coolers: Qishanr 3GS (VG32 mineral) for R-290 systems
• Walk-in freezers: Qishanr QSL-32H (VG32 POE) for R-404A systems
• Condensing units: VG32-46 depending on refrigerant and evaporator temperature

Centrifugal Compressors: Consult OEM Specifications

Centrifugal compressors often require specialty POE oils with specific additive packages for extreme operating conditions. Always follow the compressor manufacturer's oil specification for centrifugal machines.

Step 3: Adjust for Operating Temperature

Pour point and floc point become critical in low-temperature applications. The oil must remain fluid at the coldest point in the system—typically the evaporator outlet.

Low-Temperature Applications (-40°C to -60°C)

Low-temperature refrigeration systems require oils with pour points at least 10°C below the lowest evaporator temperature. Qishanr QSL-32H has a pour point of -45°C, making it suitable for most low-temperature freezer applications. For R-290 systems operating below -30°C, Qishanr 3GS with a -50°C pour point is recommended.

Medium-Temperature Applications (-20°C to 0°C)

Standard refrigeration oils are suitable for medium-temperature applications. Focus selection on refrigerant compatibility and compressor type rather than pour point.

High-Temperature Applications (HVAC, Above 0°C)

Air conditioning and heat pump systems operate at higher discharge temperatures. Thermal stability and resistance to oxidation become more important than pour point. POE oils offer superior thermal stability compared to mineral oils, with typical flash points above 250°C.

OEM Oil Cross-Reference

Many compressor manufacturers specify branded refrigeration oils. The table below cross-references common OEM oils to Qishanr equivalents.

Qishanr oils meet or exceed the performance specifications of OEM branded oils while offering shorter lead times (7 days vs 14-28 days) and flexible packaging from 1L to 200L drums.

Common Selection Mistakes and How to Avoid Them

Mistake 1: Using Mineral Oil in HFC Systems

A cold storage operator in Southeast Asia converted an R-22 system to R-404A to comply with refrigerant phase-down regulations. The retrofit included replacing the expansion valve and updating control settings, but the installer reused the existing mineral oil charge to reduce costs.

Within three weeks, the system experienced high discharge temperatures and frequent high-pressure shutdowns. Oil analysis revealed that mineral oil had separated from the R-404A refrigerant and collected in the evaporator, reducing heat transfer capacity by an estimated 35%. The evaporator required flushing, and the system was recharged with Qishanr QSL-68H. After conversion, discharge temperatures returned to normal and the system operated without fault for over 18 months.

Lesson: HFC refrigerants are completely immiscible with mineral oil. Any R-22 to HFC retrofit must include an oil change to POE and a system flush to remove at least 95% of the original mineral oil. See our HFC compatibility guide for detailed retrofit procedures.

Mistake 2: Selecting the Wrong Viscosity Grade

A maintenance contractor replaced the oil in a screw compressor cold room system with POE oil salvaged from a residential air conditioning unit. The salvaged oil was VG32, significantly lower than the VG68 specified by the screw compressor manufacturer.

After two months of operation, the compressor experienced bearing noise and elevated vibration. Teardown inspection revealed scoring on the rotor bearings caused by insufficient oil film thickness under the higher loads of the screw compressor. The lower viscosity oil could not maintain adequate lubrication at the bearing surfaces.

Lesson: Viscosity grade must match the compressor type and load conditions. Screw compressors require VG68 or higher. Scroll and small reciprocating compressors use VG32-46. Never substitute a lower viscosity grade to save costs—the compressor repair will cost far more than the correct oil.

Mistake 3: Inadequate Flushing During Retrofit

A commercial refrigeration service company retrofitted a supermarket rack system from R-22 with mineral oil to R-448A with POE oil. The crew performed a single nitrogen flush and charged the system with Qishanr QSL-46H.

Six months later, oil samples showed elevated acid numbers (0.12 mg KOH/g, above the 0.05 limit) and the system required more frequent filter-drier changes than expected. The root cause was residual mineral oil—approximately 15-20% based on the oil analysis viscosity—that remained in the system after inadequate flushing.

When mineral oil and POE oil mix, the mixture has reduced miscibility with HFC refrigerants compared to pure POE oil. This leads to poor oil return and localized oil accumulation. Additionally, mineral oil contamination reduces the POE oil's moisture-holding capacity, accelerating acid formation.

Lesson: Retrofit flushing must remove at least 95% of the original oil. For large systems, this requires multiple flush cycles with a flushing solvent or dedicated flushing equipment. Simply draining the compressor and adding new oil leaves 30-50% of the old oil in the system. Our retrofit guide provides detailed flushing procedures for various system sizes.

Decision Tree: Finding Your Oil in 3 Questions

Use this decision tree when you need a quick answer:

Question 1: What refrigerant does your system use?

• HFC (R-134a, R-404A, R-407C, R-410A, R-507A, R-448A) → You need POE oil. Go to Question 2.
• HFO (R-1234yf, R-1234ze) → You need POE oil. Go to Question 2.
• R-22 → Mineral oil or POE oil both work. If planning to retrofit to HFC in the future, choose POE now. Go to Question 2.
• Natural refrigerants (R-717 ammonia, R-290 propane, R-600a isobutane) → You need mineral oil. Go to Question 2.

Question 2: What type of compressor do you have?

• Scroll compressor → VG32-46. Small residential units use VG32. Commercial units use VG46.
• Screw compressor → VG68 for most applications. Large industrial units may require VG100-170.
• Reciprocating compressor → VG32 for small hermetic. VG46 for medium semi-hermetic. VG68 for large open-drive.
• Centrifugal compressor → Follow OEM specification exactly.

Question 3: What is your lowest evaporator temperature?

• Above -20°C (medium-temp refrigeration, AC) → Standard oils are suitable. Select based on refrigerant and compressor type.
• -20°C to -40°C (low-temp refrigeration) → Ensure pour point is at least 10°C below evaporator temperature. QSL-32H (pour point -45°C) or 3GS (pour point -50°C).
• Below -40°C (ultra-low-temp) → Specialty low-pour-point oils required. Consult Qishanr technical support.

Packaging and Handling Considerations

POE Oil is Hygroscopic

Polyol ester oils absorb moisture from the atmosphere rapidly. A partially filled container of POE oil left open for 24 hours can absorb enough moisture to exceed the acceptable limit (50 ppm) for refrigeration systems. Moisture in POE oil reacts with the ester to form acids, which attack motor windings and corrode metal surfaces.

POE oil handling rules:

• Store sealed containers in a dry location below 25°C
• Minimize exposure time when transferring oil—use a closed transfer system when possible
• Never pour oil from a large drum into an open container for later use
• Evacuate the system to below 500 microns before charging oil to remove moisture
• Use only virgin oil—never reuse recovered POE oil without laboratory testing

Qishanr packages QSL series oils in 1L, 5L, 10L, 20L, and 200L containers to minimize waste from opened containers.

Mineral Oil is Stable

Naphthenic mineral oils do not absorb atmospheric moisture and tolerate brief exposure to air without degradation. Mineral oil can be stored in partially filled containers for extended periods without moisture contamination. However, contamination with dirt, water, or incompatible oils must still be avoided.

When to Change Refrigeration Oil

Refrigeration oil in a properly maintained sealed system does not require routine scheduled changes. Oil should be replaced under the following conditions:

• Acid number exceeds 0.05 mg KOH/g — Indicates oil degradation or moisture contamination. Replace oil and investigate the root cause (leaking seals, inadequate filter-drier capacity).
• Compressor burnout — Acid and carbon contamination from motor winding failure requires complete oil change and system flushing.
• Major system repair — Any repair that opens the refrigerant circuit (compressor replacement, evaporator repair) is an opportunity to sample and replace oil if analysis shows degradation.
• Refrigerant retrofit — Converting from R-22 to HFC or from CFC to HCFC/HFC requires changing from mineral oil to POE oil.
• Moisture contamination — If moisture content exceeds 50 ppm in POE oil or 100 ppm in mineral oil, replace the oil and install fresh filter-driers.

Annual oil sampling is recommended for critical commercial and industrial systems. A qualified laboratory can test acid number, moisture content, viscosity, and contamination to detect problems before they cause failures.

Qishanr Product Recommendations by Application

For Scroll Compressor Systems

• Residential R-410A air conditioning: Qishanr QSL-32H (VG32 POE, -45°C pour point)
• Commercial R-407C rooftop units: Qishanr QSL-46H (VG46 POE, -40°C pour point)
• VRF systems with long piping: Qishanr QSL-32H for better oil return in extended pipe runs

For Screw Compressor Systems

• R-404A cold storage: Qishanr QSL-68H (VG68 POE, equivalent to Emkarate RL68H and CPI Solest 68)
• R-134a industrial chillers: Qishanr QSL-68H or QSL-100H depending on compressor size
• Large capacity process cooling: Qishanr QSL-100H, QSL-170H, or QSL-220H per OEM specification

For Reciprocating Compressor Systems

• R-290 display cases: Qishanr 3GS (VG32 mineral, -50°C pour point for low-temp applications)
• R-22 condensing units (no retrofit planned): Qishanr 3GS or 4GS mineral oils for cost-effective operation
• R-404A walk-in freezers: Qishanr QSL-32H or QSL-46H depending on compressor size

For Ammonia (R-717) Systems

• Industrial ammonia refrigeration: Qishanr 4GS (VG46 mineral) for screw and reciprocating compressors
• Ammonia systems are incompatible with POE oils — Always use naphthenic mineral oils

Technical Support and Bulk Pricing

Qishanr refrigeration lubricants are available in packaging from 1L bottles to 200L drums. All QSL series POE oils and GS series mineral oils are manufactured to meet or exceed OEM specifications and are approved for use in compressors from BITZER, Copeland, Danfoss, Carrier, Trane, York, HANBELL, Hitachi, and Fusheng.

For technical assistance with oil selection, retrofit planning, or oil analysis interpretation, contact the Qishanr technical team. Bulk pricing and private labeling are available for distributors and OEM customers.