Superheat / Subcooling Calculator

Piston superheat or TXV subcooling from line temperature, pressure, and refrigerant

Fixed-orifice systems charge by superheat (suction line temp minus suction saturation). TXV systems charge by subcooling (liquid saturation minus liquid line temp). Pick the mode that matches the metering device, enter R-410A / R-22 / R-32, and the tool flags readings outside the target band as possible overcharge, undercharge, or airflow.

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How to Use This Superheat / Subcooling Calculator

Identify the metering device first. Piston, capillary, or other fixed orifice → Superheat mode. TXV / TEV / EEV → Subcooling mode. Clamp a pipe probe on the correct line, read running gauge pressure, pick the refrigerant on the bottle — not a guess.

SH = T_suction line − T_sat (suction psig) | SC = T_sat (liquid psig) − T_liquid line

Optional indoor wet-bulb and outdoor dry-bulb tighten the piston target using a charging-chart band. Optional OEM target SC defaults to 10°F with an 8–12°F window. Walkthrough: How to Measure Superheat & Subcooling. Causes: high & low SH/SC troubleshooting. When to grab supply/return air temps instead: SH/SC vs Delta-T.

This tool does not measure airflow. If the flag says low indoor airflow, use the ESP calculator and the duct CFM calculator. It does not size duct — that is the ductulator.

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Manifolds, Probes & Charge Tools

From the TestTalkHQ HVAC Tools / Manifold Gauges catalog — digital manifolds for the pressure + line-temp pair this calculator uses, plus a scale for the charge change and a leak detector for the high-superheat path.

Fieldpiece SM380V SMAN Digital Manifold

Digital manifold with pipe-clamp probes — suction/liquid pressure and line temperature on one screen. This calculator is the independent PT check against that display.

View on Amazon →

Testo 550s AC Manifold Gauge Set with Bluetooth

Testo 550s Manifold Gauge Set

Bluetooth manifold set for R-410A / R-22 / R-32 work. Clamp the probes on the suction or liquid line, read pressure, then run the numbers here.

View on Amazon →

Yellow Jacket 46060 Digital Series 41 Manifold

Yellow Jacket 46060 Digital Manifold

Series 41 digital manifold many trucks still carry. Same psig + clamp-temp workflow as the SMAN — the PT math does not care which brand produced the two numbers.

View on Amazon →

Yellow Jacket 49967 Titan 4-Valve

4-valve charging manifold for recovering, vacuuming, and weighing in a charge after superheat or subcooling says you are short or long.

View on Amazon →

Yellow Jacket 68864 Wireless Refrigerant Scale

Yellow Jacket 68864 Wireless Scale

Weigh the charge in or out. Superheat/subcooling tells you direction; the scale is how you stop guessing ounces on a TXV or piston system.

View on Amazon →

Yellow Jacket 69354 AccuProbe II

High superheat plus low subcooling is often a leak, not a “needs more gas forever” story. Sniff before you keep adding refrigerant.

View on Amazon →

As an Amazon Associate, TestTalkHQ earns from qualifying purchases.

HVAC Refrigerant Charging Card — $3.99

Want the PT chart and charging targets on one page you can laminate? Superheat, subcooling, and R-410A / R-32 / R-454B / R-22 tables.

View on Etsy →

Superheat / Subcooling Calculator

How to Use This Superheat / Subcooling Calculator