HVAC Basics

Learn how refrigerant pressure maps to saturation temperature, why line temperature is different, and when dew or bubble references matter.

A furnace that lights and stops early may be losing flame proof, opening a limit, or ending the heat call. Use timing and safe observations to narrow it down.

Dirty filters, blower settings, coil restrictions and duct pressure can alter suction, superheat and subcooling. Learn why airflow is verified before charge.

Learn what 47°F and 17°F heat-pump capacity ratings show, why matched-system data matters, and how to compare low-temperature output without guessing.

Learn when cool air from furnace vents is normal, how fan timing and burner shutdown change the symptom, and when measurements or service are needed.

AUTO usually stops the blower with cooling; ON circulates continuously. Learn how wet-coil re-evaporation, ventilation and system design affect humidity.

Removing a furnace from a shared chimney can leave an atmospheric water heater unable to warm and draft through the oversized vent reliably.

Learn which cold-weather heat pump behaviors are normal, how to check thermostat, airflow, defrost and backup heat, and when professional testing is needed.

Learn how superheat and subcooling compare line temperature with refrigerant saturation temperature—and why neither reading proves charge alone.

Category I vents are nonpositive and noncondensing; Category IV vents are positive-pressure and condensing. The difference changes the entire vent design.