Refrigerant Oils and Blends for the EPA 608 Exam
Updated October 27, 2026
Refrigerant oils and blends come up in Core and in the retrofit questions on Type II. The key ideas: which oil goes with which refrigerant, and why most blends must be charged as a liquid. Here’s a summary, followed by free practice questions.
Lubricants
| Refrigerant family | Usual lubricant |
|---|---|
| CFCs and HCFCs (such as R-12 and R-22) | Mineral oil (or alkylbenzene) |
| HFCs (such as R-134a and R-410A) | Polyolester (POE) or polyvinyl ether (PVE) |
HFCs don’t mix well with mineral oil. That’s why converting an R-12 or R-22 system to an HFC usually means changing the lubricant. POE oil absorbs moisture readily, so keep containers sealed and limit how long a system stays open.
Blends
| Type | Behavior |
|---|---|
| Zeotropic blends (400-series, such as R-410A and R-407C) | Components boil at different temperatures, so they have temperature glide and can fractionate |
| Azeotropic blends (500-series, such as R-502) | Behave like a single refrigerant, with essentially no glide |
- Fractionation: when one component of a zeotropic blend leaks or boils off faster than the others, changing the blend’s makeup.
- Temperature glide: the difference between a blend’s bubble point and dew point at the same pressure.
- Charge zeotropic blends as a liquid, metered in on the low side so the compressor doesn’t take in liquid. Taking vapor off the cylinder would change the mix.
Retrofits
No substitute refrigerant is a true drop-in. A retrofit may need a different lubricant, new filter-driers, seals or other parts. Never mix a substitute into a system that still holds the original refrigerant.
Free practice questions
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Which lubricant is normally used with HFC refrigerants such as R-410A?Answer: BHFCs don't mix well with mineral oil, so POE (or PVE) oil is used.
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How should a zeotropic blend such as R-407C be charged?Answer: BZeotropic blends are charged as a liquid so the mix doesn't change; metering it in on the low side protects the compressor from liquid.
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What is fractionation?Answer: AIn a zeotropic blend, components boil at different temperatures. If one leaks or boils off faster, the blend's makeup changes: fractionation.
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Why must POE oil containers be kept sealed?Answer: CPOE oil is hygroscopic: it absorbs moisture from the air, which can cause acids and other problems in a system.
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What is temperature glide?Answer: DTemperature glide is the range of temperatures over which a zeotropic blend boils or condenses at a given pressure.
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An R-12 system is being converted to R-134a. What usually has to change besides the refrigerant?Answer: BR-134a isn't a drop-in for R-12. Recover all the R-12 and change to a compatible lubricant such as ester oil.
Pass the EPA 608 exam on your first try
- All 168 questions across Core, Type I, Type II and Type III
- An explanation for every answer, with the rule or principle behind it
- Unlimited practice exams per section, scored like the real test (18 of 25 to pass)