R22, R32, R410A and R407C: Physical Properties Compared, and Why Drop-in Replacement Fails

Mon, 07 Sep 2026 · HARMONY TECHNOLOGY (ZHEJIANG) CO., LTD.

R22, R32, R410A and R407C: Physical Properties Compared, and Why Drop-in Replacement Fails

The short version: R22, R32, R410A and R407C are often treated as a single “which one do I use” question. Physically they differ in three independent dimensions that drive every downstream decision: molecular composition (single substance vs. blend), flammability classification, and regulatory status under the Montreal/Kigali regimes. This note tabulates the properties and then explains the mechanism by which “drop-in” replacement fails.

1. Physical Properties Compared

Three independent dimensions — often conflated:

1. Single substance vs. blend → determines whether leakage changes composition
2. A1 vs. A2L → determines equipment and room-size requirements
3. HCFC vs. HFC → determines which regime applies (Montreal phase-out of production vs. Kigali phase-down of consumption)

An HFC blend is not “one substance with one GWP” — R407C’s GWP depends on the component ratio, and its ASHRAE number carries no CAS of its own.

2. Zeotropy: Why R407C Behaves Differently

R407C is zeotropic — its components have different boiling points, so it has a temperature glide of roughly 4–6 K across the evaporator and condenser.

Technical consequences:

• Composition shift on leakage: a zeotropic blend, leaking as vapour, loses the more volatile component first (R32). The remaining liquid becomes R125/134a-rich — the charge no longer matches the nameplate. This does not happen with R410A (azeotrope-like, ~0.1 K glide) or with R32 (single substance).
• Requires liquid charging: zeotropic blends must be charged as liquid, not vapour, to avoid fractionation.
• Counter-flow heat exchangers are used to exploit the glide and recover efficiency; a retrofit into an R22-designed exchanger loses that benefit.
• Glide must be accounted for in the evaporating temperature setpoint — the saturated suction temperature is not a single value across the coil.

3. Flammability: A2L Is a Classification, Not a Severity Scale

R32 is A2L (“lower flammability”): it has a lower flammability limit (LFL) of approximately 0.30 kg/m³, a minimum ignition energy low enough to be ignited by a static discharge in some conditions, and a burning velocity of roughly 6.7 cm/s — slow, which is precisely why it is classified 2L rather than 2.

What A2L requires that A1 does not:

Why this matters technically: an A2L refrigerant in an A1-rated system is an equipment classification mismatch — not merely a warranty issue. The relevant standard for the application (residential A/C, commercial refrigeration, or MAC) determines the allowable charge, and that figure cannot be derived from the refrigerant alone. How that allowable charge becomes a room-size limit is worked through in Refrigerant charge amount and the A2L room-size limit.

4. “Drop-in” — the Mechanism of Failure

A drop-in replacement is asserted where no drop-in exists. The mechanism, stated once:

Additional technical point on hydrocarbon “drop-ins” (R290/R600a): these are A3 (highly flammable), and their use is regulated by charge limit — often only 150 g in a single circuit for domestic appliances. Substituting them into a system designed for 1 kg of R22 is not a conversion, it is an unsafe over-charge.

Blends presented as “R22 replacements” (R417A, R422D, R427A): these are zeotropic HFC blends with glide — they still require POE (or compatible) oil, and they are still HFCs subject to Kigali phase-down. They are transitional, not exempt — the composition and glide basis that decides what a blend retrofit actually requires is set out in R404A / R507A / R448A / R449A: composition, GWP and retrofit limits.

5. Regulatory Status — Which Regime Applies

The distinction matters commercially and technically: an HCFC and an HFC in the same customs shipment are governed by different compliance instruments, require different documentation, and are counted in different units (tonnes of substance vs. tonnes CO₂-equivalent). A manifest or filing that treats “refrigerant” as one category will fail at the filing stage in either regime.

Technical reference on refrigerant physical properties and substitution mechanisms. Property data are literature values at standard conditions and vary slightly by source; equipment-specific design values must come from the manufacturer. Regulatory treatment differs by jurisdiction and year — verify the applicable instrument for the shipment’s destination and date.

What we can provide

Where the same property is quoted differently by different sources, we can supply the comparison with the basis of each figure stated, so the numbers can be reconciled instead of averaged:

• Property table per grade — GWP, ODP, critical temperature, temperature glide and saturation pressure, each with the assessment report (AR4 / AR5 / AR6) or the reference state (bubble or dew, absolute or gauge) it is quoted against.
• Glide and composition — bubble and dew temperatures at the intended evaporating and condensing conditions, plus the component mass balance of the blend, so a composition shift on leakage can be assessed rather than assumed.
• Flammability classification — ASHRAE 34 class, lower flammability limit and burning velocity for the grades offered, with the standard edition cited.
• Reconciliation of conflicting values — where two published values disagree (GWP by assessment report, glide by source), both are stated and it is made explicit which one a quotation uses.

Contact us with: the grades being compared, and the source values you are working from.

Prepared by HARMONY TECHNOLOGY (ZHEJIANG) CO., LTD. — trading company; the group’s operating entity for this product line.