NATE Low-GWP common mistakes
NATE Low-GWP · Understand the traps and how to avoid them.
Treating A2L mildly flammable refrigerants as if they carried the same handling rules as A1 refrigerants, skipping ignition-source control, charge-limit checks, and ventilation requirements during service.
Candidates carry habits from R-410A and R-22 work where flammability was never a consideration, so they overlook the A2L classification's lower flammability limit, minimum ignition energy, and burning velocity when planning a job.
What to do instead
Before every A2L job, walk through the flammability checklist explicitly: classify the refrigerant, confirm the charge against the applicable limit for the space volume and occupancy, identify and remove ignition sources, and verify ventilation. Practice stating the LFL and the classification for each common low-GWP refrigerant from memory.
Confusing GWP values across refrigerants, for example quoting R-32, R-454B, R-466A, and R-1234yf GWP figures interchangeably or using an older assessment report number instead of the current IPCC value the exam expects.
Multiple GWP figures circulate from different IPCC assessment reports and from manufacturer literature, and candidates memorize one number without noting which report or time horizon it comes from.
What to do instead
Build a reference table that pairs each refrigerant with its GWP, its source (which IPCC assessment report), and its safety classification. Note explicitly when a value is a 100-year figure versus a 20-year figure, and which value the exam's referenced standard uses.
Mishandling refrigerant identification during recovery and recycling, mixing low-GWP refrigerants in a single recovery cylinder or assuming existing recovery equipment is compatible without checking compatibility with the new refrigerant.
Candidates assume recovery practice is refrigerant-agnostic and reuse cylinders and equipment set up for legacy refrigerants, ignoring that mixing destroys the recovered charge and that some low-GWP blends require different recovery approaches.
What to do instead
Always identify the refrigerant before recovery using a refrigerant identifier, use dedicated or properly evacuated recovery cylinders, and verify equipment and oil compatibility for the specific refrigerant. Treat any unknown or mixed cylinder as unrecoverable and follow the applicable disposal rules.
Applying legacy leak-check intervals and leak-rate thresholds to low-GWP systems without accounting for the GWP-based tiering that determines inspection frequency and recordkeeping obligations.
Candidates memorize the leak-check schedule for high-GWP refrigerants and assume it transfers unchanged, missing that the regulatory thresholds are keyed to CO2-equivalent tonnage and GWP, which shifts which systems fall into which tier.
What to do instead
Work through CO2-equivalent calculations from charge weight and GWP for several example systems, then map each result to its leak-check interval and recordkeeping requirement. Practice converting between charge in pounds or kilograms and CO2-equivalent tonnes.
Ignoring oil and lubricant differences when retrofitting or servicing low-GWP systems, such as assuming a POE or PVE lubricant behaves the same with a new refrigerant or neglecting moisture sensitivity during a changeover.
Candidates focus on the refrigerant and overlook that the lubricant's miscibility, hygroscopicity, and compatibility with the new refrigerant determine compressor reliability, so they skip the oil-change and moisture-control steps.
What to do instead
For each retrofit or service scenario, state the required lubricant, its moisture sensitivity, and the required evacuation level before charging. Follow manufacturer guidance on oil change and filter-drier replacement rather than assuming the existing oil is acceptable.
Using standard pressure-temperature charts or charging methods that were developed for legacy refrigerants, leading to incorrect superheat, subcooling, or charge determination on low-GWP systems with different glide and pressure characteristics.
Candidates rely on familiar PT relationships and charging rules, but zeotropic blends have temperature glide and different pressure-temperature behavior, so the same superheat target or chart reading produces an incorrect charge.
What to do instead
Always use the refrigerant-specific PT chart and the manufacturer's charging method. For zeotropic blends, account for glide by using dew-point and bubble-point values appropriately, and verify charge by the method the equipment manufacturer specifies rather than a rule of thumb.
Overlooking that A2L refrigerants can produce toxic decomposition products when exposed to flames or hot surfaces, and failing to plan for post-fire or brazing scenarios where decomposition products may be present.
Candidates associate A2L hazards only with ignition and flammability, so they miss the secondary hazard of hydrogen fluoride and other decomposition products formed when the refrigerant contacts a flame or hot surface.
What to do instead
Include decomposition-product awareness in every job hazard review: avoid brazing on a charged system, purge with dry nitrogen, ventilate after any fire or hot-surface event, and use appropriate respiratory protection when decomposition products may be present.
Failing to verify cylinder and equipment compatibility, including valve types, pressure ratings, and whether a cylinder is rated for the refrigerant's pressure and is properly marked and within hydrostatic test date.
Candidates assume cylinders are interchangeable across refrigerants and skip the pre-job inspection, which is a common source of unsafe handling and noncompliance findings.
What to do instead
Before charging or recovering, inspect the cylinder for correct refrigerant marking, DOT or equivalent rating, and current hydrostatic test date, and confirm the valve and hose connections match the equipment. Reject any cylinder that fails inspection.
Misreading the relationship between GWP, charge size, and the regulatory or code threshold in a scenario question, for example assuming a small charge of a high-GWP refrigerant is always exempt or that a large charge of a low-GWP refrigerant is always regulated.
Candidates treat GWP and charge size as separate facts rather than a product, so they answer based on one variable and miss that the CO2-equivalent tonnage, not the raw charge, determines the requirement.
What to do instead
Practice scenario questions by computing CO2-equivalent tonnage first, then applying the threshold. Write out the calculation in the answer reasoning so the logic is visible, and check whether the question asks about charge, GWP, or the product.
Skipping the safety-data and labeling review before handling an unfamiliar low-GWP refrigerant, relying on general knowledge instead of the SDS and equipment nameplate for classification, charge, and handling limits.
Candidates assume all low-GWP refrigerants behave similarly and skip the documentation, missing differences in flammability classification, toxicity, and the manufacturer's specific charge and handling limits.
What to do instead
Make SDS and nameplate review a standard first step: confirm the safety classification, the maximum charge, and any manufacturer-specific handling limits before starting work. Treat the SDS as the authoritative source for hazards and first aid, not memory.