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Some quick basics: An ohmmeter is used to measure the resistance to electrical flow between two points. The ohmmeter is most commonly used to check continuity. Continuity is not a “measurement” as much as it is a yes/no statement. To say there is continuity is to say that there is a good electrical path between […]

A while back, I had a tech who was having some trouble finding a 35 PSI (2.41 bar) make-on-fall pressure switch. One adjustable switch in the catalog said (SPDT), but he didn't quite understand what that meant. In that case, it means single-pole, double-throw, and the “double-throw” part means that the switch has terminals in both the […]

  The most common—and often most frustrating—questions that trainers and senior techs get asked sound something like this: “What should my ______ be?” or “My _____ is at ______. Does that sound right?” Usually, when the conversation is over, both the senior and junior techs walk away feeling frustrated because the junior tech just wanted […]

Delta T is the difference in temperature between two points of the same medium. It is commonly used by scientists and engineers to analyze the amount of heat transfer in a system. In general HVAC terms, it is the measurable change in temperature between an air input and air output. However, it could also be […]

In this article, we’ll discuss solving superheat using this diagnostic sheet to help us better understand how it is calculated and from where it is derived. I want to thank Ty Branaman for helping me develop these sheets that will hopefully aid in a better understanding of some of the basic HVAC measurements that both […]

Let's start with the basics. Water freezes at 32° Fahrenheit (0° Celsius) at sea level and at atmospheric pressure. When any surface is below that temperature, and the air around it contains moisture, ice/frost will form. You can see how water freezes at the molecular level in the GIF below:   In some situations, ice […]

This is a basic overview of the HVAC/R refrigerant cycle (and refrigeration circuit) and how it works. It isn't a COMPLETE description by any means, but it is designed to assist a new technician or HVAC/R apprentice in understanding the fundamentals. First, let's address some areas of possible confusion:  1. The word “condenser” can mean […]

I teamed up with Ty Branaman to design an intuitive way for techs to solve some of the “what should it be?” questions in the HVAC field.  The topic for this sheet is subcooling (or subcool). Subcooling is a measurement of the temperature DECREASE of a liquid below its saturation (mixed liquid/vapor) temperature at a […]

This is the article you read BEFORE you call and ask a senior tech what your subcooling should be. It's also the one you send to a junior tech when they call and ask you: So, what is subcooling? (Or subcool, as many call it.) Subcooling is a measurement of the temperature DECREASE of a […]