I received an email from a homeowner in Wisconsin today that said this: “We recently had a 3 1/2-ton split system installed, but since its installation this unit has performed poorly. I was reviewing the service manual and see that the refrigerant in the unit is R-410A, and I know the installer added 5 lb. of R22 at time of installation. The service manual specifically states only R-410A should be used and as I understand, these two products work at very different pressures and use different lubricants. I came across an article you wrote about this today and I’m wondering what your opinion is as to why this unit has been doing such a poor job of cooling our home?”
Well, I know that to any of you who have ever attended a course on basic refrigeration, it sounds unbelievable that any HVACR installer or service technician would do such a stupid thing. However, I have come across many technicians and even company owners who believed they could improve a system’s performance by giving it a shot of another refrigerant. Yet, all this does is reduce the capacity and efficiency of the system and eventually leads to its failure. Why? Let’s take a look at those pressure differences.
In order to achieve proper cooling, the low-side vapor pressure of R22 in an A/C system must drop to a pressure of somewhere between 60 to 70 psig. However, the low-side vapor pressure of R410a in the same type of system typically is in the 100- to 120-psig range. As you can see, the R22 cannot possibly evaporate or do any cooling since the mixing puts it under too much pressure, so it just floods back to the compressor as a liquid, which dilutes the lubricant and reduces its lubricating abilities. Then to make matters worse, the R-22 is trying to squeeze through the same metering orifice as the R410a, so less of the working refrigerant is reaching the evaporator to do any cooling.
Let’s take a look at the charge; a typical R410a condensing unit is shipped with the proper charge for most systems, which is about 6.5 to 7 lb. So all the installer has to do is pull a triple (dilution) vacuum on the system to remove any air and moisture, then open the condensing unit valves for the proper charge — done and walk away.
However, in this case the installer said he added 5 more lb. of (the wrong) refrigerant to the existing charge. This overcharge drastically raises the head pressure of the compressor and the system draws far more electricity while shortening the compressor life. The question is: How did he get a low-pressure refrigerant into a high-pressure environment? To quote an old Maxwell Smart line, “Very carefully!”
So, does this mean you can’t mix refrigerants? No, because R410a is itself a mixed refrigerant. This is called an azeotropic blend, which means they have mixed refrigerants of the same basic pressure and weight. Why? The best refrigerant likely has an unfavorable characteristic (such as flammability or toxicity) and they blend it with a less-efficient refrigerant to dilute the undesirable effects.
But then, why would anyone put the extremely rare and expensive refrigerant R22 in an R410a system? Who knows? Rather, unqualified technicians everywhere are putting R410a into R22 systems with the same catastrophic results. We know that because recycling companies tell us most of the refrigerant they are getting back today has been mixed.
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