Saturation Temperatures

One of the great things about writing this blog has been the friendships I have made with other folks involved in HVACR education. People write and share their ideas, or just send me a thumbs up on something I have said that they agree with or appreciate. They also let me know when I have overlooked something or suggest changes for the book. Believe me, David and I work very hard trying to make Fundamentals of HVACR a valuable resource to help you teach. We really do appreciate all the comments and ideas. This week I wanted to pass along an idea from Thomas Bush at South Florida Community College. 

Thomas writes:

“This past year I’ve found myself referring almost exclusively to saturation temps on both the high and low side, rather than pressures, when working with the students in the lab. That’s really the important reading, whether you’re measuring superheat, subcooling, or even just ball-parking and older system. All of our gauges have 22 and 410a PT charts built in. We have dedicated sets for 134a. Seems like talking saturation temps takes the whole 22/410a question out of the equation. A 40° evap temp is a 40° evap temp no matter what refrigerant you’re using.”

I really like this idea. It reinforces why particular pressures are important. Eventually, the students/techs will get used to seeing 120 - 135 psig suction pressures on R410 systems, but they will know where the pressures came from. The pressure reading will not just be a random number. I believe emphasizing the saturation temperatures can also reinforce why we have a high side and a low side in the first place. With all the new refrigerants coming out, it is especially important that technicians understand why they are looking at a particular pressure. If you know the saturation temperature you are looking for, then a PT chart is all you need to find the pressure for a brand new refrigerant you have never worked with before. If you are fortunate enough to have one of the new digital gauge sets that can hold 40 different refrigerants, you may already have the PT chart built into your gauges. Many of these automatically display the saturation temperature as well as the pressure. Thanks to Thomas Bush for sharing his idea. I am sure the folks down in South Florida will have plenty of time to practice it soon. If anyone else would like to share a tip or successful idea, please don’t be shy! 

How much refrigerant does it take to make the fan blow harder?

Have you ever noticed that right after you buy a car you seem to see that particular model everywhere?  Similarly, once you solve a problem, every problem you see seems to be another iteration of that same problem. My theory is that we are programmed to repeat our successes. The brain says “that worked before, lets do that again!” We are all occasionally tempted by the same quick fix demon that whispers in our ear “this worked the last time!” The temptation is just to repeat our latest success without really looking carefully at the actual problem before us. We convince ourselves that this problem is just like the previous one. I think it is more difficult for younger technicians to resist the quick fix temptation. They have not seen as many problems, so their brain is less confused – it is certain the solution is whatever they have seen recently! Often the quick solution involves adding refrigerant. My brother Richard is a senior technician at his company. Having seen and experienced many things, other technicians often call him for help. Richard is also a joker, so they know they are going to have their tail twisted a bit when they call. Recently a young tech called Richard and said he could not get the suction pressure on an R22 unit above 50 psig even though he had added refrigerant three times and every time the pressure settled down to 50 psig. He didn’t understand why adding refrigerant did not raise his suction pressure. Richard asked him “how many pounds of refrigerant do you have to add to make the fan blow harder?” No reply. So he asks again “Say, I really don’t know, how many pounds of refrigerant DOES it take to make the fan blow harder?” Finally, the tech replies: “adding refrigerant won’t make the fan blow any harder no matter how much I add.” Richard then asks “so why are you trying to fix an airflow problem by adding refrigerant?” Of course there are several possibilities that could cause low suction pressure, but airflow is one of the most common.  He could also have some type of refrigerant restriction or a metering device issue. However, more information is needed to differentiate these from each other. A high superheat and low subcooling could indicate an undercharge. A low superheat could indicate an airflow problem. A high subcooling and high superheat would point to a refrigerant restriction or metering device issue. The problem is that the tech was only looking at the suction pressure and nothing else. He had already decided what the problem was and how to fix it before actually finding the problem. To his credit, he did recognize that he was pursuing the wrong “fix,” that is why he called for help. The next time you can’t understand why your fix is not working, ask yourself if you are trying to make the fan blow harder by adding refrigerant. Then call Richard.  

Dr. William Lipscomb

I heard on the radio that Dr. William Lipscomb had recently passed away at the age of 91. I confess that I really had no idea who he was. I became a little more interested when the announcer reported that he taught chemistry t Harvard and had won the Nobel Prize for chemistry. There aren’t many people that have done that. Then I became really interested when they said three of his former students had also won Nobel prizes. To me, that is really a much greater achievement. The mark of a good teacher is not what he has done, but what his students have done. He accomplished more by being a great teacher than he could have possibly done individually. I had to Google him to learn more. When I did, I found out that he was a student of another famous Nobel prize winning teacher – Linus Pauling. One of the quotes attributed to Dr. Lipscomb was “For me, the creative process, first of all, requires a good nine hours of sleep a night. Second, it must not be pushed by the need to produce practical applications.” I love this guy and I never met him. Here is a Nobel prize winning Harvard professor saying he is motivated by a need for practical application. This week’s posting is dedicated to celebrating the life of a great teacher, Dr. William Lipscomb. 

Digital Gauges

Digital gauges are becoming more common. The first company to offer digital manifold gauges was Digicool. When the first Digicool gauge sets came out, only the air conditioning techno-geeks and tool hounds had them. It will still be a few years before most mechanics use digital gauges, but many companies that traditionally make gauge manifold sets now have a digital offering. The list includes companies like JB, Refco, Robinair, and Yellow Jacket. Even companies who do not traditionally sell gauge manifolds offer digital manifold sets, including Field Piece and Testo. Many of these are billed as digital system analyzers because they do more than read pressure. They also show saturation temperature and have a place to plug in a thermocouple temperature probe for reading line temperatures, providing all the information necessary to determine system superheat and subcooling. Many will calculate the system superheat and subcooling and display them in real time. Some will even suggest what the target system superheat and subcooling should be based on the system operating conditions. There are several digital analyzers available that will also read vacuum in microns, doubling as a deep vacuum gauge.  The strongest argument for digital gauges is accuracy. They are more accurate than the best bourdon tube gauges can hope to be. Accuracy is becoming increasingly important as system operating efficiency becomes more important. 


The prices are coming down, but you will still pay a premium for a digital set over a good quality analog set. If you decide to take the plunge here are a few things to consider. When comparing the cost of a digital gauge set that reads deep vacuum, remember that a vacuum gauge alone can easily cost $200. Also remember that you are buying a manifold, not just a set of gauges. So sets that come on better manifolds cost more, just like analog gauge sets. One caveat when shopping - there are some very inexpensive digital gauge manifolds advertised on line that are intended specifically for cars and 134a. They will NOT work on systems which use other types of refrigerant, especially not R410a! These days you really should not consider investing in a high tech tool that will not work with R410a.


 However, in the next few years I expect the same type of technology/price inversion that we have seen with electric multimeters where the older technology actually costs more than the newer technology. When Fluke digital meters were first being used in HVACR, they typically were more expensive than their analog counterparts of comparable quality. Now, a Simpson 260 analog VOM costs more than a Fluke 116 multimeter, and the Simpson is less resistant to field abuse and really less useful for the HVACR technician in general. The older technology electric meter technology is actually more expensive than the newer digital meters. I realize the analogy is imperfect: a Simpson 260 analog VOM is considerably more complex than a bourdon tube gauge.  However, I expect digital gauge sets  to be in the same price range as good quality analog bourdon tube gauge sets within 5 years.


  

Good Company

It is often said that you can judge a person’s true character by the company they keep. One of the prime benefits to the two major instructor conferences is meeting with a large group of people who share your enthusiasm for teaching HVACR. My posting is a little late this week because I have been out of town pursuing my avocation – music. I play trombone in the Macon Symphony Orchestra. I say avocation because for me, it is like grown men going to baseball camp. I get to play with a really great group of musicians and they pay me for it to boot! We played three concerts this weekend, the last one for a group of orphans. Several kids were allowed to come up on stage and sit during one of the pieces. They literally were right in the middle of the orchestra. When one young man headed towards the lower brass, our tuba player, Heather, excitedly said “that’s my 7^th grade tuba player!” You see, Heather teaches band at a local school during her day job. He sat right in front of us while we played. Not only did he get to hear the orchestra, he saw his teacher performing in a professional group. Heather is hooked on teaching. She talks about her students, what they are doing, and how they are progressing. She has managed to find a way to combine two loves into a profession: music and teaching. I hope that is the way you feel about teaching HVACR. Teachers receive the unique opportunity to share in other people’s success. If you approach teaching this way, you will be rewarded by the company you keep. After several years of teaching, you will find yourself in good company as your students develop into professionals who love what they do and give you more credit that you deserve for helping them along the way.