Tech Tips

Why is it called single-phase 240 when there are two opposing phases (or legs)? I wondered why we called two 120v opposing legs “single-phase 240” for years. Then someone pointed out to me that a typical “single-phase” pole transformer only has one power leg entering and two coming out. That freaked me out. How can […]

Flowing nitrogen while brazing does not mean the air was cleared first. Learn how to purge large ACR piping, choose a practical regulator setup, and estimate time and cylinder use.

First off, the correct acronym for a GFI (ground fault interrupter) is “GFCI” (ground fault circuit interrupter). The purpose is to act as a safety device to protect from electrical shock. GFCIs are important components of electrical safety; they even make an appearance in our electrical safety video. GFCIs can be built into outlets, circuit […]

It’s always good to reaffirm some of the basics of energy, work, and matter. The five rules below are some of the most basic and important. The First Law of Thermodynamics States that energy cannot be created or destroyed. It can only change forms or be transferred from one object to another. If you’d like […]

Condensate overflow prevention devices, or float switches, as they are often called, are such simple devices that you wouldn’t think there would be much room for controversy. In my experience, there are few areas of the trade where technician and installer preferences and opinions vary greatly. Let’s start with some float switch basics. Float (condensate) […]

I once heard someone say, and I have since repeated many times, that BTUs ride on the back of cubic feet of air (CFM). As I’ve learned more, I’ve come to the conclusion that the weight or mass of the air passing over the evaporator coil is far more important to understand both in terms […]

Callbacks are horrible. They kill the trade from every possible angle. They destroy customer satisfaction and reduce technician morale by causing long hours, resulting in unprofitability for companies and overall less earning opportunity for everyone. Possibly worse of all, callbacks tell customers that you are no better than their cousin the maintenance man, or worse, […]

In HVAC/R, we are in the business of moving BTUs of heat, and we move BTUs via pounds of refrigerant. The more pounds we move, the more BTUs we move. In a single-stage HVAC/R compressor, the compression chamber maintains the same volume no matter the compression ratio. The thing that changes is the number of […]

A commonly taught method for measuring airflow is the temperature rise method, where you use a heat source that produces a set number of BTU/h, such as heat strips. Then, using the sensible heat air equation, you can “easily” calculate the CFM being produced by the equipment. Let’s use this specific example to illustrate the […]