Refrigerant Properties, Safety, and Handling
What R-410A actually is
R-410A is a near-azeotropic blend of R-32 (50%) and R-125 (50%). Its temperature glide is only about 0.1–0.2 °F, so in the field it behaves much like a single refrigerant - but because it is a blend, it must always be charged and recovered as a liquid. Vapor-charging a blend can fractionate it and leave the cylinder with the wrong composition.
Properties that drive exam numbers
R-410A runs roughly 50–70% higher pressures than R-22 at the same saturation temperature, contains no chlorine (ODP 0), has a GWP near 2,088, and requires POE oil, which is strongly hygroscopic. It is ASHRAE A1 - low toxicity, no flame propagation - but that is not the same as harmless: liquid flashing to vapor at atmospheric pressure causes frostbite and eye injury, and the vapor is heavier than air and can displace oxygen in pits, basements, and low crawl spaces.
Safety and handling essentials
Never heat a cylinder with an open flame or take it above about 125 °F; use warm water or a heat blanket. Cylinders are DOT-rated, must not be overfilled, and must never be used to hold a refrigerant they are not labeled for. Manifolds, hoses, and gauges must be rated for R-410A service; R-22 gauges can fail at these pressures. Wear gloves and eye protection whenever cracking a line or charging liquid.
Traps
"The blend can be topped off as a vapor" - false. "R-410A is a drop-in for R-22" - false; different oil, pressures, and metering. "Because it is A1 it needs no PPE" - false.
Rule of thumb
At a given saturation temperature, R-410A pressure is about 1.5–1.6× the R-22 value; a 40 °F evaporator sits near 118 psig.