One of the very first steps when it comes to diagnosing your home air conditioner, refrigerator, or even your vehicle’s air conditioner is understanding the temperature and the current pressure that your system is operating at. Having these facts along with the saturation point, the subcool, and the superheat numbers for the refrigerant you are working on are essential when it comes to really understanding what is going wrong with your system.
After a visual inspection the very next step for the most seasoned technicians is pulling out their gauges and checking the pressure and temperature. It just becomes second nature after enough calls. I have heard stories of rookie techs calling some of the pros on their team for help on a system that they’re stuck on. It doesn’t matter what the situation is. It doesn’t matter if you’re in Miami or in Fargo. It will never fail that one of the first questions the pros ask the rookie is what is your subcool and what is your superheat? Having and understanding these numbers is key to figuring out what to do next.
But, these numbers won’t do you any good if you don’t know what refrigerant you are dealing with and what the refrigerant’s boiling point is at each pressure level. This article aims at providing you with just that information.
R-12 Pressure Chart
R-12 is one of those classic refrigerants that nearly everyone has heard of before. Even if you are not part of the industry chances are you have heard of R-12. You see, R-12 is a CFC refrigerant and was one of the first artificially created refrigerants to see widespread usage. It was in the 1930’s that the DuPont corporation teamed up with General Motors to come up with a safe, reliable, and cheap refrigerant. All of the previous refrigerants like ammonia, propane, isobutane, and even carbon dioxide all had their own problems. Sometimes it was flammability, toxicity, or operating pressure. Regardless of why these natural refrigerants weren’t working it was clear that the market needed a different kind of refrigerant.
It was during this partnership that we began to see the rise of artificial refrigerant classifications known as CFCs and HCFCs. Only shortly after their invention these new refrigerants began to take the world by storm. Not more then thirty years later and you could find R-12 all over the world in all kinds of different applications. Its explosive growth continued over the years. So did the related refrigerants known as R-11, R-22, R-502 and many others. The world was being filled with CFC and HCFC refrigerants.
It was in the 1980’s that a team of scientists discovered that these refrigerants did have a downside… and it was a big one. You see if these refrigerants were vented into the atmosphere either through damage, mistake, or malfeasance the chlorine in these refrigerants would make its way up into the Stratosphere. In here the sun’s ultraviolet rays would break down the chlorine. This broken down chlorine would chip away at what’s known as the Ozone layer. Eventually a hole developed which caused the world to band together and create a global treaty known as the Montreal Protocol. The treaty aimed at phasing out all of these Ozone damaging refrigerants.
One of the first refrigerants to go was our friend R-12. At this point in time, in the early 1990’s, R-12 had seen the majority of it’s usage in automobile air conditioning. R-12 was banned in new automobiles and was replaced with by the HFC refrigerant we all know today as R-134a. Now, there are still some R-12 applications out there today. Most of these are through antique car collectors but there are other applications out there as well.
If you are working on an R-12 machine you are going to need to know your pressures. Let’s take a look at our pressure chart. (Note that the first few pressure values are in Vacuum inches in Hg.):
|Temp (F)||Temp (C)||Pressure (PSIG)|