#temperature

Tech Tips:

We’re in the business of moving heat, but we have to move air to accomplish that. We use CFM (cubic feet per minute) to quantify the air we move over the indoor coil, and it helps to imagine hundreds of 1’x1’x1’ boxes of air moving over that coil each minute. (After all, 400 CFM is […]

Does Mass or Volume Move Heat?

I once heard someone say, and have since repeated many times that BTU's ride on the back of Cubic Feet of Air or 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 […]

The PATH to High Performance HVAC w/ David Richardson

In this engaging session, David Richardson breaks down the concept of high-performance HVAC, offering a clear roadmap for industry professionals looking to elevate their craft. Richardson argues that the HVAC industry has long been focused on equipment rather than complete systems, leading to widespread inefficiencies. The average system delivers only about 57% of its […]

How to Evacuate an AC system, Full Vacuum Procedure

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HVAC School – For Techs, By Techs

Real training for HVAC ( Heating, Ventilation, Air Conditioning and Refrigeration) Technicians. Including recorded tech training, interviews, diagnostics and general conversations about the trade.

In this episode of the HVAC School podcast, host Bryan discusses superheat with guest JD, who recently co-authored an article on the topic with Ty Branaman. The conversation explores the often misunderstood concept of superheat, its importance in HVAC diagnostics, and common misconceptions technicians have when measuring and interpreting it.

Bryan begins by sharing how superheat was initially taught to technicians in the late 1990s and early 2000s, primarily as a method for charging fixed metering device systems. He explains how this limited view led to problems, as technicians would often add or remove refrigerant based solely on superheat readings without considering other system factors or giving the system time to stabilize. JD points out how the industry shifted when TXVs (Thermostatic Expansion Valves) became standard, with many technicians abandoning superheat measurements altogether in favor of subcooling measurements, missing crucial diagnostic information in the process.

The discussion then evolves into a more sophisticated understanding of superheat as an indicator of evaporator coil “fullness.” Bryan explains that lower superheat indicates a fuller evaporator coil, while higher superheat suggests a starved coil. They discuss the importance of measuring superheat in the correct location, noting that TXVs control superheat at the evaporator outlet, not at the condensing unit where technicians often measure. This misunderstanding leads to many incorrect diagnoses of “bad TXVs” when the real issues might be related to airflow, heat pickup in line sets, or other factors. Both experts emphasize the value of measuring superheat both inside at the evaporator outlet and outside at the condensing unit to get a complete picture of system operation.

Key Topics Covered:

Definition of superheat and its importance in HVAC diagnostics
How superheat indicates evaporator coil “fullness” (flooded vs. starved conditions)
The distinction between charging by superheat and using superheat as a diagnostic tool
Common misconceptions about superheat measurement on TXV systems
Why measuring superheat location matters (evaporator outlet vs. condensing unit)
How to properly diagnose TXV issues using superheat measurements
The relationship between airflow problems and superheat readings
Normal superheat ranges for residential systems (7-14 degrees at evaporator outlet)
How superheat affects both system capacity and compressor safety
“Exercising” TXVs as a troubleshooting technique
How line set conditions and installation factors can impact superheat readings
System behavior during “hot pull down” conditions when starting with high indoor temperatures

JD and Ty’s superheat tech tip and worksheet: https://hvacrschool.com/solving-superheat/

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