Recently, I read where a supply-house manager asked this question: “What happens when a service tech adds R410a to an R22 air-conditioning system?”

He added, “Everyone is doing it!”

Here’s how we achieve mechanical refrigeration with the use of a refrigerant gas. You take a chemical that is a gas at normal atmospheric pressures (such as R22) and compress it. This makes it very hot because you have the same heat compressed into a smaller space. Then you move the gas through a finned copper coil and cool the gas down, which causes it to condense into a liquid. With R22, for example, this happens when you cool it to about the outdoor temperature. And on a 90° F day, the pressure of that gas (R22) is at least 168 psig, which causes it to condense into a liquid (look at a refrigerant pressure-temperature chart).

Then we squirt the pure high-pressure liquid refrigerant through a metering orifice into a lower-pressure environment (the return or suction side of a compressor) and run it through a finned copper evaporator coil. At the lower pressure the liquid refrigerant boils or evaporates and this creates the cooling. On an R22 system where the indoor temperature is being maintained at 75°, the coil must operate at about 50° to sufficiently cool the air and the pressure will be about 84 psig.

Now let’s look at the pressures required to do the same cooling using R410a. The high-side pressure needed to compress R410a into a liquid at 90° is 274 psig. The low-side pressure required to cause R410a to evaporate at 50° is 142 psig. And since this is almost twice the pressure that the R22 liquid requires to evaporate, R22 clearly cannot evaporate in an environment where the higher-pressure R410a is present. So, any R22 in the system that is mixed with R410a returns to the compressor as a liquid.

A bit of an oversimplification? Yes, but you get the idea.

The point is the R22 isn’t doing anything: it’s just returning to the compressor as a liquid. And a rule of nature tells us it is impossible to compress a liquid.

Does this hurt anything? Since the liquid R22 is not evaporating or cooling, it is blocking the flow of R410a through the metering orifice, which drastically cuts the system’s cooling capacity. Also, the liquid R22 (which is a solvent) mixes with and dilutes the compressor lubricant, which soon will cause the compressor to seize and stop running. In addition, compressor valves are made to open under the pressure of a gas, not a liquid, and if the compressor doesn’t seize up first, the valves will break and the compressor will stop compressing. Mixing the gases destroys the compressor.

Also, the same thing is true when mixing R22 with R407C or R417A. Both of these supposed “R22 replacements” evaporate at a lower pressure than R22, so they don’t fully evaporate in a higher-pressure environment where R22 is present either, which causes these refrigerants to return to the compressor as a liquid, and this (at least) dilutes the compressor lubricant and cuts the system cooling capacity.

Interestingly, while I was at the AHR Expo in Chicago in January, I stopped to talk to some people at a refrigerant-recovery company and they told me that despite all the phase-outs, they have quite a glut of R22 on hand because nobody is buying it!

Yes, the price is quite high, but using the proper refrigerant surely is worth the added expense when the alternative is a greatly-reduced system capacity and a much shorter compressor life!