Saturday, April 30, 2011

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! 


  1. One instructor posted on that he puts tape over the pressure scale on the manifold gauge set to teach his students the value of reading the temps...sounds like a great idea!

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