Refrigerant Types, Classes and A2L Safety

Chemical Classes

HFCs and HFOs are "substitutes" under Section 608. You still need certification to buy them, and you may not vent them, unless the specific substitute and use is exempt in 40 CFR 82.154(a).

ASHRAE 34 Safety Classes

The letter shows toxicity: A is lower toxicity and B is higher. The number shows flammability: 1 means no flame propagation, 2L means lower flammability with a low burning velocity, 2 is flammable and 3 is higher flammability.

What A2L Means on the Job

• Use recovery machines certified for flammable refrigerants. Under 40 CFR 82.158 these are tested to appendix B4, which draws on AHRI 740 and UL 1963 Supplement SB.
• Check for ignition sources and ventilate the work area. Follow the equipment maker's instructions.
• Use cylinders and fittings marked for the refrigerant. Many flammable-refrigerant cylinders use left-hand threads. Check the label.
• Charge blends such as R-454B as liquid, because blends can fractionate.

Pressure Groups in the Regulation

Section 608 groups appliances by the refrigerant's saturation pressure at 104 °F. Low-pressure is below 45 psia, medium is 45–170 psia, high is 170–355 psia, and very high is above 355 psia (or a critical temperature below 104 °F). The group sets the required evacuation level, which is covered in the EPA 608 recovery and evacuation requirements.

Ozone Depletion Potential and Global Warming Potential

Two numbers describe a refrigerant's environmental impact. Ozone depletion potential (ODP) measures how much a substance damages the ozone layer compared with CFC-11, which has an ODP of 1. Global warming potential (GWP) measures how much heat a substance traps compared with carbon dioxide over a set period, usually 100 years. CFCs and HCFCs have ODP because they contain chlorine. HFCs have zero ODP but many have high GWP, which is why their production is now being phased down. HFOs and natural refrigerants have zero ODP and low GWP.

The Phaseout and the Phasedown

Production of CFCs ended in the United States under the Montreal Protocol and the Clean Air Act. HCFCs such as R-22 have also been phased out of new production, and servicing now relies on recovered, recycled and reclaimed supplies. HFCs are covered by a separate phasedown under the American Innovation and Manufacturing (AIM) Act of 2020, which EPA implements under 40 CFR Part 84. That is why new equipment is moving to lower-GWP refrigerants such as R-32 and R-454B.

Single-Component Refrigerants and Blends

Some refrigerants are a single chemical, such as R-22, R-134a or R-32. Others are blends of two or more components.

• Azeotropic blends (the 500 series, such as R-502) behave like a single substance and boil at one temperature at a given pressure.
• Zeotropic blends (the 400 series, such as R-410A, R-404A and R-454B) have components that boil at slightly different temperatures. The difference is called temperature glide.

Zeotropic blends can fractionate, which means the components separate when the blend changes phase. A leak can change the blend's makeup, and charging as vapour from the cylinder can deliver the wrong mix. That is why blends are charged as liquid, metered into the system to avoid slugging the compressor.

Oils

Refrigerant and compressor oil travel together. CFC and HCFC systems traditionally used mineral or alkylbenzene oils. HFC systems generally use polyolester (POE) oil, and automotive systems often use polyalkylene glycol (PAG) oil. POE and PAG oils absorb moisture readily, so keep containers sealed and limit the time a system is open. Always follow the equipment maker's oil specification.

Reading the Refrigerant Number

The ASHRAE 34 numbering system tells you something about each refrigerant. Numbers in the 400 series are zeotropic blends and the 500 series are azeotropic blends. The 600 series covers miscellaneous organic compounds such as isobutane (R-600a), and the 700 series covers inorganic compounds, where the last digits give the molecular weight: ammonia is R-717 and carbon dioxide is R-744.

Retrofitting

When an older system is converted to a different refrigerant, technicians call it a retrofit. A retrofit may require an oil change, new seals or a different expansion device. Never mix refrigerants in a system or top up one refrigerant with another. Label the system clearly with the refrigerant and oil it now contains.

Exam Tips

• Chlorine is what makes a refrigerant ozone-depleting.
• HFCs have zero ODP, but they are still covered by the venting ban and sales restriction.
• Zeotropic blends have temperature glide and should be charged as liquid.
• A2L means lower toxicity and lower flammability.

Identifying an Unknown Refrigerant

Always check the equipment nameplate first. If the nameplate is missing or you suspect the system has been retrofitted or mixed, a refrigerant identifier can analyse a sample before you recover it. Recovering an unknown mixture into a clean cylinder of one refrigerant contaminates the whole cylinder.

Temperature-Pressure Relationships

A single-component refrigerant in a container with both liquid and vapour has a pressure that matches its saturation temperature. Technicians use pressure-temperature charts to check this. For zeotropic blends, the chart gives separate bubble point and dew point values because of temperature glide. Exam questions may ask you to recognise that a pressure that doesn't match the saturation temperature can point to non-condensables or a mix of refrigerants.

Key Terms

• ODP: ozone depletion potential, compared with CFC-11.
• GWP: global warming potential, compared with carbon dioxide.
• Substitute: a refrigerant that replaces an ozone-depleting refrigerant, such as an HFC or HFO.
• Azeotrope: a blend that behaves like a single substance.
• Zeotrope: a blend with temperature glide that can fractionate.
• Bubble point and dew point: the temperatures at which a zeotropic blend starts to boil and finishes boiling at a given pressure.
• Retrofit: converting a system to a different refrigerant.

Common Exam Traps

• Thinking zero ODP means the venting ban doesn't apply.
• Charging a zeotropic blend as vapour.
• Confusing the A/B toxicity letter with the flammability number.
• Assuming R-22 is a CFC. It's an HCFC.

Quick Questions

Is R-32 a blend?

No. R-32 is a single-component HFC with an A2L safety class. It is also a component of blends such as R-410A and R-454B.

Why is R-454B replacing R-410A?

R-454B has a much lower global warming potential, which helps manufacturers meet the AIM Act phasedown and its technology transition rules for new equipment.

Can I put R-454B into an R-410A system?

Not as a drop-in or top-up. Systems are designed and certified for a specific refrigerant, and A2L refrigerants need equipment designed for them. Follow the manufacturer's instructions.

What is the difference between HFC and HFO?

Both contain no chlorine, so both have zero ODP. HFOs are unsaturated compounds that break down quickly in the atmosphere, so their GWP is very low, while many HFCs have high GWP.

Why does R-410A run at higher pressure than R-22?

Each refrigerant has its own pressure-temperature relationship. R-410A has a higher saturation pressure at the same temperature, so equipment, hoses and gauges must be rated for it.

Which refrigerants are natural?

Common natural refrigerants include ammonia (R-717), carbon dioxide (R-744) and hydrocarbons such as propane (R-290) and isobutane (R-600a).

Test yourself with the EPA 608 Core practice test.