Category Trade Guides

A furnace tune-up checklist for technicians: safety checks, combustion, airflow, temperature rise, electrical tests and what to record before you leave.

In May 2026 the EPA removed the installation deadline for R-410A systems built before 2025. Here is what changed, what did not, and what technicians should know about R-454B and R-32.

A failed run capacitor is one of the most common air conditioner faults. Learn how to test one safely with a meter, read the tolerance and choose a replacement.

GFCI devices protect people from electric shock. AFCI devices protect buildings from fires caused by arcing. Here is how each works and where each is used.

Superheat and subcooling tell you what refrigerant is doing inside a system. Learn the definitions, how to measure each one and what high or low readings mean.

A beginner's guide to the multimeter for service technicians: measuring voltage, resistance, continuity and current, choosing the right setting and working safely.

Ohm's law links voltage, current and resistance. Here are the formulas, worked examples on real equipment, and how they help you troubleshoot in the field.

A reference of common HVAC conversions and formulas: BTU, tons, kilowatts, horsepower, pressure, airflow and water flow, with worked examples.

MERV ratings describe how well an air filter captures particles. What the numbers mean, how filters affect airflow and how to choose a filter that suits the system.

A guide to low-voltage thermostat wiring: what the R, C, W, Y, G and O/B terminals do, the usual wire colors, heat pump wiring and how to avoid a blown fuse.