EPA 608 refrigerant types explained (2026): families, A2L, and the AIM Act

If you came here to figure out which certification to take, that is a different question. Start at certification types or the what is EPA 608 overview.

One page unifies the refrigerant families, the ASHRAE safety classes, zeotropic and azeotropic blends, oil compatibility, R-410A, and the 2026 A2L transition, all framed as the questions the Core and Type II sections throw at you. The naming convention is your cheat code. R-12 is CFC-12, R-22 is HCFC-22, R-134a is HFC-134a, R-1234yf is HFO-1234yf. Decode the number, name the family, answer the question.

What are the main refrigerant families on the EPA 608 exam?

The exam does not want you to memorize 60 refrigerants. It wants you to sort any refrigerant into one of five families by the atoms it carries. Walk the chain CFC to HCFC to HFC to HFO to hydrocarbon, and the ozone story tells itself.

CFCs (chlorofluorocarbons) contain chlorine, fluorine, and carbon. The exam names are R-11, R-12, R-500, and R-502, all fully phased out under the Montreal Protocol. Because they carry no hydrogen, they are chemically stable, so they survive the lower atmosphere and drift into the stratosphere intact. Once UV light frees it, a single chlorine atom can destroy up to 100,000 ozone molecules.

HCFCs (hydrochlorofluorocarbons) add hydrogen to the mix. That hydrogen makes them less stable, so more of the molecule breaks down before it reaches the ozone layer, giving them a lower ODP. R-22 (the old residential AC workhorse), R-123 (centrifugal chillers), and R-124 are the ones to know.

HFCs (hydrofluorocarbons) drop chlorine entirely: just hydrogen, fluorine, and carbon. No chlorine means an ODP of zero. R-32, R-134a, R-404A, R-407C, and R-410A all live here, and they all require POE oil. HFOs (hydrofluoroolefins) add a carbon-to-carbon double bond, and R-1234yf is the headliner with a GWP under 1 and an A2L safety rating. Hydrocarbons and naturals round out the set: R-290 (propane) and R-600a (isobutane) are A3, and R-717 (ammonia) is B2L.

How does the ASHRAE safety classification system work (and what is A2L)?

Every refrigerant on the exam carries a two-part safety code from ASHRAE Standard 34, and the Core and Type II sections ask you to read it. The letter is toxicity. The number is flammability. Get both and you can classify anything on the sheet.

Toxicity is simple: A means lower toxicity (occupational exposure limit of 400 ppm or higher), B means higher toxicity (OEL below 400 ppm). Flammability runs on a scale. A rating of 1 is no flame propagation, 2L is mildly flammable with a burning velocity at or below 10 cm/s, 2 is flammable, and 3 is highly flammable. The lowercase "L" in 2L stands for low burning velocity, and that single letter is the whole 2026 story.

A1 is the safest class and where most legacy refrigerants sit: R-410A, R-22, R-134a, R-404A, and R-407C. A2L is the new arrival that trips up techs raised on A1-only systems. R-32, R-454B, and R-1234yf are A2L: low toxicity, mildly flammable, but with a slow, low-energy burn that is a fundamentally different hazard from a propane tank. A2L is a mild, controllable class, not "just flammable," which is exactly why the exam added it.

The extremes still matter. A3 covers the hydrocarbons like R-290 propane and R-600a isobutane, which ignite readily. B1 is R-123, toxic but non-flammable. B2L is ammonia (R-717), toxic and mildly flammable at once.

Zeotropic vs azeotropic blends: glide, fractionation, and liquid charging

Blends separate techs who memorized from techs who understood. The tested distinction is whether the components in a blend behave as one substance or as several, because that decides how you charge it and how it leaks.

Zeotropic blends carry ASHRAE 400-series numbers and mix refrigerants with different boiling points. As the blend evaporates or condenses, its temperature slides across a range instead of holding steady. That range is temperature glide, the difference between the dew point and the bubble point at constant pressure. R-407C runs about 11.5°F of glide (dew point 21.94°F, bubble point 10.44°F), which you have to account for when you measure superheat and subcooling. R-404A, despite being a 400-series blend, is near-azeotropic with roughly 1°F of glide.

Azeotropic blends carry 500-series numbers and behave as a single substance with essentially zero glide. R-502 is the exam favorite: R-22 at 48.8% and R-115 at 51.2% by weight. R-500 is another. Both boil and condense as if they were one refrigerant.

Glide creates two problems the exam loves. First, fractionation: because the components have different vapor pressures, they leak at different rates, and the composition left in the system drifts away from spec. That hits R-407C hardest. Second, charging: you must charge a zeotropic blend as a liquid, never vapor, or the most volatile component enters first and the ratio is wrong from the start. Never combine refrigerants yourself. A self-mixed blend is illegal under EPA rules, cannot be reclaimed, and carries fines.

Which oil goes with which refrigerant?

Pick the wrong oil and the system starves. Refrigerant oil has to be miscible with its refrigerant, meaning it blends and travels with it. If it does not, the oil never returns from the evaporator, pools in the low side, and starves the compressor. Miscibility is a requirement, not a preference.

Mineral oil pairs with the old chlorine-bearing refrigerants, CFCs and HCFCs like R-12 and R-22. Alkylbenzene (AB) oil also serves CFC and HCFC systems, mixes with mineral oil, and bridges some retrofits. Neither belongs in a modern HFC system.

POE (polyolester) is the oil the exam ties to R-410A and every other HFC and HFO: R-32, R-454B, R-134a. Two rules define it. POE cannot be mixed with any other oil, and POE is hygroscopic, meaning it pulls moisture straight out of the air. That absorbed water reacts with the refrigerant through hydrolysis to form acid, so POE systems have to stay sealed and dehydrated. Leave a POE container open on the truck and you have already started degrading it.

Two more round out the list. PAG (polyalkylene glycol) is automotive R-134a only, not stationary HVAC, so do not carry a car-AC habit onto a rooftop unit. PVE (polyvinyl ether) is an alternative to POE for HFC and HFO systems where POE does not fit.

R-410A: the refrigerant the Type II exam leans on

If Type II has a signature refrigerant, it is R-410A, and the exam tests it from several angles at once. It is a near-azeotropic HFC blend of R-32 and R-125 at roughly 50/50, with an ODP of 0, a GWP of 2,088, and an ASHRAE A1 rating. It runs on POE oil.

The number that matters in the field and on the test is pressure. R-410A operates about 60% higher than R-22. At 95°F ambient, that looks like roughly 135 PSIG suction against R-22's 70 PSIG, and around 380 PSIG discharge against R-22's 260 PSIG. Those pressures are exactly why you cannot retrofit R-22 equipment to R-410A. The components are not built to hold it.

Watch the trap. R-410A carries a 400-series number, which screams zeotropic and significant glide. In practice it behaves near-azeotropically, with glide so small it charges and reads like a single-component refrigerant. Expect a question that dangles "large temperature glide" as a tempting wrong answer for R-410A.

R-410A also sets up the 2026 storyline. It is the high-GWP HFC being phased down under the AIM Act, and knowing its chemistry is the on-ramp to its A2L replacements. Recover it under 40 CFR Part 82 and the Clean Air Act, the same as any regulated refrigerant, and route it to a certified reclaimer rather than the atmosphere. The Core study guide covers the recovery rules that pair with this chemistry.

What color are refrigerant cylinders now?

Older study material actively lies to you on cylinder color, so read this section as a correction. Since January 2020, under AHRI Guideline N (2016 update), all new virgin refrigerant containers ship in one uniform color: RAL 7044 silk gray, a light green-gray. The unique color-per-refrigerant system is gone.

The change was a voluntary U.S. guideline, not a federal mandate, driven by refrigerant proliferation. As the number of refrigerants grew, the old color codes stopped helping and started causing confusion, and more than half of surveyed handlers said so. Flammable refrigerants (A2L, A2, A3) get one added marker: a red band on the cylinder.

The exception is the one the exam cares about most. Recovery cylinders were not touched by the 2020 shift. They stay gray body with a yellow top, the DOT standard for recovery and recycling, and that combination is the single most-tested cylinder fact on the Core exam.

Legacy colors still appear in old prep books, so recognize them as history, not current practice: R-22 light green, R-410A rose or pink, R-134a sky blue, R-404A orange. If a study source lists those as current, it is out of date. Drift like this is why we built our 569-question bank the way we did: every fact sits in a verified facts table with a source citation, and each question passes a 3-layer validation (structure check, fact check against the table, explanation review) before it goes live.

A2L and low-GWP refrigerants in depth: GWP values, HFOs, and service rules

What does GWP actually measure?

GWP (global warming potential) measures how much heat a gas traps in the atmosphere over 100 years, relative to carbon dioxide. CO2 is the reference, so its GWP is 1 by definition. A refrigerant with a GWP of 2,088 traps 2,088 times more heat than the same weight of CO2 over that century. That is the entire concept, and the exam tests it as a definition question.

Do not confuse GWP with ODP. ODP (ozone depletion potential) measures ozone destruction relative to R-11 at 1.00, and it is about chlorine. GWP is about heat trapping, and even chlorine-free refrigerants like R-410A score high on it. A refrigerant can have zero ODP and a huge GWP, which is exactly the HFC problem the AIM Act targets.

One wrinkle worth knowing before you drill numbers: GWP values shift slightly depending on which IPCC assessment report a table uses. Most US datasheets and EPA SNAP listings use AR4 values, which is why R-410A shows 2,088 in this guide (AR5 lists 1,924). Memorize the AR4 numbers below; they are what US prep material and providers quote. If drilling by card beats rereading tables for you, the flashcards on our app cover these GWP values and the other pure-recall numbers on this page, free with an account.

What counts as low-GWP under the AIM Act?

The working threshold is 700. Under EPA's technology transitions rule, new residential and light commercial AC and heat pump systems manufactured or imported after January 1, 2025 must use a refrigerant with a GWP below 700. R-454B at 466 and R-32 at 675 clear the bar. R-410A at 2,088 does not, which is why its equipment era ended.

The law behind the threshold is the AIM Act (American Innovation and Manufacturing Act of 2020). It phases down HFC production and consumption through an allowance system, stepping down from a 2011-2013 baseline to 15% of baseline by 2036, an 85% total cut. Know the steps: 90% of baseline in 2022-2023, 60% for 2024-2028, 30% for 2029-2033, 20% for 2034-2035, and 15% from 2036 on.

One regulatory distinction earns you a point on Core. The HFC phasedown is codified at 40 CFR Part 84, a separate part from the 40 CFR Part 82 rules that govern your day-to-day recovery, venting, and certification obligations under Section 608. The phasedown restricts production allowances, not field service: recovering, reclaiming, and recharging existing R-410A systems stays legal. The full timeline, including the July 2026 rule that lets pre-2025 R-410A inventory be installed until it runs out, lives in the AIM Act changes guide.

How do HFOs get a GWP under 5?

HFOs (hydrofluoroolefins) are the chemistry story the exam wants in one sentence: an HFO carries a carbon-to-carbon double bond, and that unsaturated bond makes the molecule fall apart fast. R-1234yf breaks down in the lower atmosphere in about 11 days. R-134a, its saturated HFC cousin, hangs around for roughly 14 years. GWP is driven by how long a gas survives, so an 11-day lifetime collapses R-1234yf's GWP to 4 on AR4 tables and under 1 on AR5. If the why behind that still feels slippery, the AI Tutor in our app can rephrase it until it clicks; a free account includes 10 tutor questions a month, and Pro raises that to 1,000.

The naming gives HFOs away. Four digits after the R means an unsaturated molecule, so R-1234yf reads as HFO-1234yf the same way R-134a reads as HFC-134a. Decode the number and you have answered the family question before reading the choices.

HFOs show up on the exam two ways. Pure, as R-1234yf, the automotive AC standard since the 2017-2021 model years, running pressures within about 5% of R-134a. And as a blend component: R-454B is 68.9% R-32 plus 31.1% R-1234yf, and that HFO fraction is what drags the blend's GWP down to 466.

Which low-GWP refrigerant replaces which system?

The exam frames the transition as a mapping exercise: legacy refrigerant on one side, successor on the other. Four pairings cover nearly every question.

R-454B (sold as Puron Advance, Opteon XL41, or Solstice 454B) is the pick of most major US residential manufacturers. R-32 dominates mini-splits, runs 3-5% more efficient than R-410A, and is a pure compound rather than a blend, so no glide or fractionation concerns.

The rule that outranks every pairing: no retrofits. An R-410A system cannot be converted to R-454B or R-32, full stop. A2L refrigerants require equipment engineered for them, with leak sensors, airflow logic, and A2L-rated components built in. Any answer choice describing an A1-to-A2L retrofit procedure is wrong before you finish reading it.

What changes when you service an A2L instead of an A1?

A2L means lower toxicity, mildly flammable, with a burning velocity at or below 10 cm/s. The flame is slow and low-energy, nothing like propane, but it exists, and every handling difference on the exam flows from that fact. Your A1 habits are the wrong answers now.

Two details separate a pass from a guess. First, leak detectors are refrigerant-specific: an instrument calibrated for R-410A may not reliably read R-454B, so A2L work requires a detector rated for the refrigerant in the system, sensitive to at least 5 grams per year, and intrinsically safe. Second, ignition control is procedural, not optional: purge with nitrogen before brazing, keep open flames out until the space is verified clear, and let vapor disperse rather than pool, because A2L vapor is heavier than air.

Recovery itself follows the same 40 CFR Part 82 rules you already know. A2L refrigerants are regulated refrigerants, venting is prohibited, and your Section 608 card is the federal credential that covers handling them. The Core study guide covers those recovery and venting rules in full.

Where do natural refrigerants fit?

Naturals are the floor of the GWP table, and the exam uses them to test whether you can separate climate numbers from safety classes. R-744 (CO2) has a GWP of exactly 1 because it is the reference gas. R-290 (propane) and R-600a (isobutane) sit at 3. R-717 (ammonia) scores 0.

Here is the trap: the lowest-GWP refrigerants are not the easiest to handle. CO2 is A1 and non-flammable but runs transcritical supermarket racks at pressures far beyond anything in residential work. Propane and isobutane are A3, highly flammable, and confined to small-charge self-contained cases and household refrigerators. Ammonia is B2L, both toxic and mildly flammable, and stays in industrial plants.

So each natural trades its near-zero GWP for a different burden: pressure, flammability, or toxicity. That trade-off is why A2Ls, and not naturals, won the residential transition. A question that implies "lowest GWP = safest choice" is testing exactly this.

Who decides which refrigerants you're allowed to use?

The SNAP program (Significant New Alternatives Policy) is the gatekeeper, and it predates the AIM Act. SNAP runs under Section 612 of the Clean Air Act, codified at 40 CFR Part 82 Subpart G. Before any substitute refrigerant reaches your gauges, EPA evaluates it on four axes: ODP, GWP, toxicity, and flammability.

Every substitute lands in one of three buckets: acceptable, unacceptable, or acceptable subject to use conditions. That third bucket is where the A2L era lives. Use conditions are enforceable requirements, things like charge limits, required leak sensors, and equipment listing standards, and R-454B and R-32 systems carry them. EPA has kept adding listings as the transition accelerates, including proposed SNAP Rule 27 for residential and light commercial equipment.

For the exam, keep the division of labor straight. SNAP decides which substitutes are legal and under what conditions. The AIM Act decides how much HFC can be produced each year. Section 608 and 40 CFR Part 82 decide how you, the certified tech, must handle all of it in the field.

The AIM Act: deadlines, phasedown, and what changes for certified technicians

If you are already certified, here is what actually changes

Your certification status does not change. EPA 608 certification has no expiration date, and the AIM Act adds no recertification requirement. The passing standard for the exam is also unchanged: 18 of 25 (72%) per section, with Universal covering all four sections for 100 questions total. What changes is operational, and it applies to the work, not the card.

• New equipment uses A2L refrigerants. R-454B and R-32 are now standard in new residential systems, and they handle differently from R-410A.
• Expanded leak and recordkeeping duties. The AIM Act HFC Management Rule layers reporting and leak repair obligations on top of the Section 608 framework.
• A2L safety knowledge is expected. Many employers ask for voluntary A2L training even though it is not federally mandated.

2026 deadlines and the R-410A phasedown

Beginning January 1, 2025, the AIM Act Technology Transitions Rule limited production of R-410A based equipment. New residential HVAC equipment built in 2025 and beyond primarily uses A2L refrigerants, R-454B and R-32, with GWP far below R-410A (466 and 675 respectively, versus R-410A at 2,088).

R-410A itself remains available for servicing existing systems through current supply channels and reclamation. Only new equipment production is affected, so you will service R-410A systems in the field for decades as existing equipment stays in use.

A2L refrigerants on the EPA 608 exam: R-454B, R-32, and R-1234yf

A2L refrigerants are classified as mildly flammable under ASHRAE Standard 34. They need UL or ETL listed tools, proper ventilation, and A2L rated recovery equipment. The Type II section now includes A2L content, so a technician trained only on R-410A needs to understand the safety differences before servicing new equipment.

If the ASHRAE class letters and numbers are new to you, the safety-class section above decodes A1, A2L, A3, and B2L with the exam facts for each.

For the full low-GWP picture (GWP values to memorize, HFO chemistry, and the phasedown steps), see the low-GWP refrigerants exam guide.

R-454B (Opteon XL41): the primary replacement for R-410A in new residential and light commercial split systems. GWP of 466, about 78% lower than R-410A. Already the dominant refrigerant in new residential equipment.

R-32: used in some new residential split systems as a standalone refrigerant. GWP of 675. Mildly flammable (A2L).

R-1234yf: the primary replacement in automotive MVAC systems (covered by Section 609, not 608), though technicians meet it in some commercial refrigeration applications.

New leak detection requirements under the AIM Act

The AIM Act HFC Management Rule expanded leak duties beyond the Section 608 framework. For larger equipment, it can require automatic leak detection rather than only periodic inspection, and it broadens reporting and recordkeeping. The exact charge thresholds and effective dates vary by equipment type and are set in the HFC Management Rule itself.

AIM Act HFC phasedown timeline

EPA 608 refrigerant types FAQ