Every charge check is the same dance: gauge readings, line temps, a PT chart, and mental math in a 130°F attic. The math hasn't changed since forever — so we turned it into a free calculator that does the whole dance in under a minute.
Fixed orifice: target superheat
Indoor wet-bulb + outdoor dry-bulb → target superheat. Measure actual (suction line temp minus saturation temp), compare: actual high means undercharged or starved; low means overcharged or poor airflow. The calculator takes your two temperatures and hands you the target — no interpolating a laminated card.
TXV systems: subcooling
The TXV holds superheat for you, so you charge by subcooling against the nameplate target (commonly 8–12°F). Liquid line temp, liquid pressure → saturation temp, subtract. The tool does the PT conversion inline for R-410A, R-22 and R-32.
The mistakes it catches
- Charging a TXV system by superheat (the valve fights you)
- Skipping the airflow check first — low airflow mimics undercharge; a static pressure check takes two readings
- Chart interpolation errors at 5 PM on the fifth call of the day
🌡 Open the Charge Calculator →
Free. No login. No email wall.
Bookmark it — it lives with 134 other free tools in the hub, superheat targets to wire sizing.