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One of several refrigerants a technician may have put into an R-22 system instead of replacing it. If your equipment label says R-22 but a service sticker says R-438A or MO99, that is what happened. The practical consequence is the same as any blend retrofit: tell any future technician before they touch the charge.
What is R-438A?
R-438A is HFC blend (zeotropic) with hydrocarbon oil-return additives, specifically 8.5% HFC-32 / 45% HFC-125 / 44.2% HFC-134a / 1.7% n-butane / 0.6% isopentane by weight. It is also sold and referred to as 438A, MO99, Freon MO99. Its ASHRAE Standard 34 safety classification is A1 — low toxicity, non-flammable, and its global warming potential is about 2,265.
Ozone depletion potential: zero. It is not an ozone-depleting substance.
What equipment uses it, and when was it common?
R-438A was common in residential equipment 2010 to the present. R-22 retrofit refrigerant. Not used in new residential equipment.
Is it still used in new equipment?
No. New residential systems manufactured or imported from January 1, 2025 must use a refrigerant with a GWP under 700, and R-438A is above that limit.
Can existing systems still be serviced?
Yes. Existing R-438A systems can be serviced and recharged. Components used to repair existing systems are not restricted by the technology-transition rules, and there is no requirement for you to replace working equipment.
Is it compatible with other refrigerants?
Approved for use in R-22 equipment: yes. Approved for use in R-410A equipment: no.
Marketed as a lower-effort R-22 retrofit because its hydrocarbon additives help return mineral oil, which can avoid a full oil change in some systems. Still a retrofit procedure with manufacturer-specific requirements, not a drop-in.
Never assume two refrigerants are interchangeable because their pressures or performance look similar. Compatibility is a property of your specific equipment, established by its manufacturer, not a property of the refrigerant alone.
What does it cost?
We do not track a separate installed price benchmark for R-438A. It is a retrofit refrigerant rather than a routine stock item, so pricing varies more than for the mainstream refrigerants and is best quoted directly.
Why does service cost more than the refrigerant?
Retrofit blends are lower-volume products, and diagnosing a system whose label and actual contents disagree takes longer.
Beyond that, every refrigerant invoice carries a licensed technician’s time, EPA Section 608 certification, recovery and evacuation equipment, refrigerant carried as truck stock, insurance, and a warranty on the work. The quote checker breaks a real invoice into those parts.
How much might a residential system contain?
As a planning estimate, a typical residential system holds roughly 2 to 4 pounds per ton of cooling capacity — about 6 to 12 pounds for a common 3-ton system. That is an estimate, not a specification: actual charge depends on the indoor coil match and the line set. Estimate your own system.
What should you ask your technician?
- Can you show me where R-438A is listed on my equipment?
- What is the expected total charge for this model?
- How much are you adding today, and was the system weighed?
- Where do you think it leaked from, and did you perform a leak search?
- Is the leaking component under manufacturer warranty?
All 20 questions, grouped by when to ask them →
When does repair versus replace become the real question?
When the repair is a large share of replacement cost, when the equipment is past roughly 12 years, or when the leaking component is a coil or compressor outside warranty. A refrigerant phase-down on its own is not a reason.
Work through the repair-or-replace decision →
Where this site stops
We will help you understand your equipment, read your invoice, and ask better questions. We will not tell you how to buy refrigerant, connect gauges, or charge a system. Opening a sealed refrigerant circuit requires EPA Section 608 certification under federal law, and there is no homeowner exemption. Venting refrigerant is separately illegal. This is genuinely a licensed-technician job, and the reason is legal as much as technical.
Related: Refrigerant hub · Find my refrigerant · Refrigerant timeline · AC repair vs replace
Frequently asked questions
Can R-438A be used in my system?
Only if your equipment’s manufacturer approves it for that equipment. R-438A is approved for R-22 equipment: yes. For R-410A equipment: no. Similar operating pressures never make two refrigerants interchangeable.
Is R-438A still available?
Yes. Existing systems using R-438A can still be serviced and recharged.
What is the GWP of R-438A?
About 2,265, computed from the component exchange values published in Appendix A to 40 CFR Part 84.
Sources & verification
✓ Verified against a manufacturer, regulator, or standards source
- GWP values computed from the component exchange values in Appendix A to 40 CFR Part 84, the AIM Act regulated-substance list, rather than copied from secondary sources — epa.gov
- EPA, “Technology Transitions HFC Restrictions by Sector” — epa.gov
⚠ Provisional — market-survey estimate, not a manufacturer or regulator citation
- No installed-price benchmark is tracked for this retrofit refrigerant; pricing is best quoted directly.
Last reviewed 2026-08-31. How we verify what we publish →
