How to identify an unknown refrigerant

Start with the nameplate

The outdoor unit’s nameplate names the refrigerant and the factory charge. Rheem’s R-454B instructions, for example, work from the “Factory Refrigerant Charge Weight listed on the nameplate,” and they require the installer to write the total system charge on a label next to it. Check the indoor coil’s label as well, and look for any retrofit tag on the unit.

A2L equipment has extra markings you can look for. EPA’s SNAP use conditions for A2L refrigerants in residential and light commercial AC (Appendix W) require:

• Permanent warnings on the outside of the unit: “WARNING—Risk of Fire. Flammable Refrigerant Used.”
• A warning inside, near the compressor.
• Red PMS #185 or RAL 3020 marking at service ports, pipes and hoses, extending at least 1 inch in both directions from each opening.
• On the indoor unit near the nameplate, a minimum room area (and, where UL 60335-2-40 requires it, a minimum installation height).

Red-marked ports mean a flammable refrigerant. They do not tell you which one.

Service ports and fittings

On stationary equipment, the service port is not a reliable clue. Neutronics’ Mini ID spec sheet gives “the common service ports and the similarities between R22 and replacement refrigerants using pressure temperature charts” as the reason knowing what is in a unit “is often difficult.”

Vehicles are different. EPA requires a unique set of fittings for each refrigerant approved for MVAC, and its unique fittings table lists them. R-134a uses quick-connect ports. R-1234yf uses SAE J639 (2020) quick-connects of 17 mm (high side) and 14 mm (low side) outside diameter, and its 30-lb cylinders have a left-hand thread. EPA states that an adapter may not be used to convert a fitting.

Cylinder labels, not colors

AHRI Guideline N-2017 moved all new refrigerant containers to one color, light green-gray RAL 7044. A red band on the shoulder or top marks refrigerants that are flammable or could become flammable. The guideline says colors “should not be relied upon exclusively to determine the type of Refrigerant” and that the color scheme “is not a substitute for reading cylinder labels and markings.” Older painted cylinders are still in circulation. The legacy colors and the red band are on the cylinder colors page.

A recovery cylinder’s label tells you only what someone wrote on it. If the tag is missing, or the history of the cylinder is unknown, treat the contents as unknown.

The standing pressure check

EPA lists the “use of pressure and temperature to identify refrigerants and detect noncondensables” as a Type I test topic, and “how to identify refrigerant in appliances” under Type II. The method:

1. Use a cylinder that has rested, or a system that has been off long enough to equalize. The check needs the system off, not running.
2. Measure the temperature of the refrigerant, not the air. Take it on the cylinder wall or the line where liquid sits. A cylinder that has been in the sun or a hot truck is not at ambient temperature.
3. Read the pressure with a gauge you trust, at the same moment.
4. Compare with the bubble column of a PT chart for each candidate. The liquid sets the pressure, so read bubble on blends. The PT calculator will give the value at any temperature.

Worked example: R-22, R-410A or R-454B at 75°F

Bubble-point pressures from this site’s PT data:

R-22 stands well apart. At 75°F it is more than 75 psi below either of the other two, and a cylinder of R-22 would have to be about 106°F to read 215 psig.

R-410A and R-454B are the hard pair. At 75°F they are 10.3 psi apart, but each changes by about 3.3 to 3.5 psi per °F around that temperature. Say the gauge reads 215.0 psig:

• If it is R-410A, the cylinder is at about 73.9°F.
• If it is R-454B, the cylinder is at about 77.0°F.

A thermometer that is off by 3°F, or a cylinder wall that has not caught up with the room, swaps the answer. On R-454B, the column matters too: its dew-point pressure at 75°F is 199.5 psig, almost 9 psi below the bubble value. Reading the wrong column shifts the match by nearly as much as the gap between the two refrigerants. R-410A vs R-454B compares the two across the full range.

Where the check fails

• Air and other non-condensables add pressure on top of the refrigerant’s own. A contaminated cylinder reads higher than any chart value and can land on the wrong refrigerant. Fieldpiece’s MR45 manual uses exactly that sign: when cylinder pressure is “higher than expected,” you may have non-condensables at the top.
• Mixtures of two refrigerants sit somewhere between their charts and match neither.
• Leaked blends. EPA lists fractionation, “tendency of different components of blends to leak at different rates,” as a core topic. A blend system that has leaked and been topped off may no longer match its own chart.
• No liquid. A nearly empty cylinder or a system with almost no charge holds only vapor and reads below the chart. The PT relationship holds only where liquid and vapor coexist; see how to read a PT chart.

Use the check to rule refrigerants out. Rheem’s troubleshooting table lists “wrong refrigerant or mixed refrigerants” as a cause of unusual head and suction pressures, which is one reason operating pressures alone are not a test.

Refrigerant identifiers

Handheld identifiers take a sample from the system or cylinder through a hose and analyze it. Bacharach and Mastercool describe non-dispersive infrared (NDIR) sensing. What they detect depends on the model:

None of these documents lists R-454B. Before you trust a result on an A2L system, check the current refrigerant library for your instrument. The Legend flier mentions remote software updates for new refrigerants.

The makers pitch the same use. Check the system before recovery so you do not contaminate a recovery cylinder. Wholesalers and reclaimers screen incoming cylinders the same way.

Unknown or mixed refrigerant

If the label, the PT check and an identifier do not agree, or you have no identifier, do not charge with it and do not add it to a clean recovery cylinder.

1. Recover it into its own cylinder. Use an evacuated recovery cylinder, keep it under the 80% fill limit, and label it with what you know: “mixed” or “unknown,” the source and the date. The recovery guide covers cylinder prep.
2. Purge non-condensables if air is the only problem and the refrigerant is otherwise known. Fieldpiece’s method transfers vapor into a second evacuated cylinder until the full one reads 5 psi above its chart pressure.
3. Send it to a consolidator or certified reclaimer and tell them it is mixed. Under 40 CFR 84.104, recovered refrigerant may go to a new owner only for reclamation or destruction, or after an EPA-certified reclaimer has reprocessed it to the AHRI 700 specifications. The Legend flier makes the cost point: less mixed gas recovered means less refrigerant that has to be destroyed.

Never vent it to get rid of it. Knowingly releasing refrigerant after recovery is a violation of the venting prohibition (40 CFR 82.154(a)(3)).