Understanding Refrigerant Retrofits

R-22 specified equipment makes up the largest portion of the current U.S. air conditioning residential installed base, and over the past few years the price of R-22 refrigerant has increased to the point where homeowners are starting to look for alternatives. Reasons for this search are typically tied around a system that has a leak, as refrigerant does not “wear out” or lose “potency” over time. Recently, this website has received several inquires about using R-410A to supplement this “loss of charge” situation amongst the R-22 install systems.

Can R-410A charge be added to “top off” an R-22 system?

The short answer “NO.”

To better understand this answer, let’s briefly take a look at each of these refrigerants. R-22, which is a HCFC (Hydrochlorofluorocarbon), is currently the most commonly found refrigerant in U.S. AC systems. ARI lists AC condition points as (45°F/130°F) for an R-22 (azeotropic) are listed as 297psig / 76psig. Service technicians use a PT (pressure/temperature) chart to understand these conditions and relate them back to a known pressure/temperature correlation. This means that a technician will use his manifold gauges (typically a “red’ and “blue” gauge set) to find the system pressures at a particular point, while the system is running. This pressure will then be used with the PT Chart to determine the temperature and chemical state of the refrigerant in that portion of the system. R-410A (zeotropic), which is an HFC (Hydrofluorocarbon), is listed under the same ARI condition points of (45°F/130°F) is 477pisg / 130pisg. When comparing the pressures of R-410A to that of R-22, R-410A is almost twice the pressure per the same temperature. Again, a service technician would also use this pressure/temperature correlation to determine the R-410A system conditions and the basis for making any adjustments.

Because each of these refrigerants has a known pressure/temperature point, which is determined using a known chemical manufacturers’ PT chart listing, mixing two different refrigerants with two completely different pressures, would produce a mixture of a new chemical blend without a known pressure/temperature correlation.  In other words, what chart would a technician use to determine system conditions containing a mixture of the two different refrigerants?  Along this same line, there are several other problems like mineral oil (use with R-22) and its lack of miscibility with R-410A refrigerant …but I think you get the point, and hopefully understand the answer a little better.

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10 thoughts on “Understanding Refrigerant Retrofits

  1. do you think even if mixing is possible the compressor that work for R-22 can handle a double pressure refrigerant R-410A.

    • Naqshabandi,

      Compressors and systems are designed to operate with specific refrigerants. Any deviations could lead to performance, reliability and other problems including safety problems.

    • Charlie,

      A rough estimate might be around 7 lbs. But factors like, condenser SEER, evaporator size, and even temperature/density of the gas could effect this amount.

      I would recommend using a system charging calculator as a guide.


  2. I just had a new ac system installed . We upgraded to the 410A freon system. Quick question, Is there a problem using the same line-set after flush , and if is so what would be the solution?

    • There should not be a problem with using the former line set, as long as the lines are the proper size and are designed for R-410A pressures. Also, an effort should be made to remove as much of the former oil as possible. However, please keep in mind that due to heat and vibration the copper lines can become brittle and may develop leaks over time. So, if it is possible to replace the old line set, I would recommend it. No one wants to pay for a new system to be installed, only to have the former line set fail a few months later.

    • Unless you have an existing problem with your thermostat, replacing the thermostat is a matter of choice. Modern Thermostats typically have a more accurate temperature reading and can offer more setback programming features. Other new features might be humidity control, Wi-Fi, color screens and zoning just to name a few. Thermostats can be purchased through most big box stores or through your local energy provider. But I would recommend getting a HVAC Technician involved, one who can help with the actual change out, provide programming tips and help with the set up as it relates to your particular system.

  3. AC keeps shutting off. I will turn off for a few minutes then turn back on and it runs for another 4 to 8 hours.

    • Sounds like you’re A/C system is shutting off on some type of protector or safety control. Shutting the power off to the system is electrically resetting the control long enough for the system to continue operating for another run cycle. If your system continues to run (without stopping) for the next 4 to 8 hrs a cycle, then it is probably suffering from a low or loss of charge scenario. I would recommend having a qualified HVAC Technician service the unit.

      Hope this help,

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