I ran into a Carrier unit yesterday that had the old compression type access valve on the suction line. I realized that there are probably many techs working today that may have never seen one of these. They were common in the late 1970’s. Most units came that way, with compression fittings for the refrigerant lines. Every manufacturer had their own type of compression nuts and ferrules. Sometimes the ferrules were shipped with a plastic plug in them and the nut hand tightened. More than once I had a unit where the nut was a little too tight and the ferrule was compressed around the plastic plug, making it useless. I don’t expect we will see those return, but I wanted to point out that what was once commonplace is no longer even recognized by most people in the field. I am sure there is technology that is common today that will seem equally strange in another 30 years. Knowing the mechanical fine points of today’s equipment is valuable for working efficiently, but that information will be next to useless in ten years. Understanding how and why systems operate and why things are done the way they are is more lasting. The physics behind the basic refrigeration cycle has not changed in 30 years and is not likely to change in another 30 years because it is based on laws of physical science. What types of connectors the refrigerant lines have, what the metering device looks like, what wires are used for control, what type of motors a unit has, or even what type of compressor it has can all change drastically in 30 years. What won’t change are the concepts of saturation, pressure temperature relationship, superheat, and subcooling. Learn all you can about why systems work because that knowledge will be the foundation you will use for understanding tomorrow’s systems. Knowing which heat pumps available today energize the reversing vale on orange and which energize on blue probably won’t be a lot more useful than being able to differentiate a Carrier ferrule from a York ferrule is today. By the way, here is what the Carrier compression access valve looks like.