Field Notes
Plain-language writing on HVAC/R service: charging, airflow, vacuum, controls, gas heat and the new A2L refrigerants. Written for people already on the tools, not for a classroom.
Latest notes
The Gas Furnace Ignition Sequence, One Step at a Time
Every modern furnace lights in the same order. Know the order and you know where to look when it stops.
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Recovery Cylinders: Fill Limits, Colors and Safe Handling
The 80 percent rule, the gray and yellow paint and the retest date all exist for the same reason: liquid refrigerant expands.
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Mini Split Flares That Don't Leak
Many mini split leaks start at a flare. A square cut, a clean flare and the right torque prevent nearly all of them.
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Reading a PT Chart Without Getting Fooled
A PT chart only works where liquid and vapor exist together. Here is where that is, where it is not, and how to use the chart to diagnose.
Read more →HVAC know-how, in plain language.
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14 free practice quizzes
Ten questions per topic, from the refrigeration cycle to gas furnace ignition.
Free · No account needed · Every answer explained