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
Superheat or Subcooling? How to Know Which One Sets the Charge
Both readings come from the same gauges, but only one of them tells you about the charge on a given system. The metering device decides which.
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What 500 Microns Really Tells You About a Vacuum
Hitting 500 microns is only half the test. What the gauge does after you isolate the pump tells you whether the system is dry and tight.
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Check Airflow Before You Touch the Gauges
Low airflow imitates a low charge almost perfectly. Ruling it out first saves you from overcharging a system that only needed a filter.
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No-Cool Call? A Ten-Minute Triage Before You Hook Up
Most no-cool calls end at something simple: power, the thermostat, a float switch or a capacitor. Here is an order of checks that finds them fast.
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Testing a Run Capacitor the Right Way
A weak run capacitor causes hard starts, hot motors and nuisance trips. Here is how to test one safely and read the result.
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R-32 and R-454B on the Job: What Actually Changes
New residential systems now run on A2L refrigerants. The physics is familiar; the tools, cylinders and habits around them are not.
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14 free practice quizzes
Ten questions per topic, from the refrigeration cycle to gas furnace ignition.
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