CalcPanel

Superheat & Subcooling Calculator

Check AC and refrigeration charge from pressure and line temperature. Built-in R-410A, R-22, R-404A, R-134a, R-454B PT charts. Example: at 120 PSI R-410A the saturation temperature is 55°F; a suction line at 65°F gives 10°F superheat. Also estimates target superheat for fixed-orifice and TXV metering devices.

Calculator

Pick a mode, choose the refrigerant, then enter gauge pressure and line temperature. Use the Target Superheat mode to confirm charge on a fixed-orifice system from outdoor and indoor conditions.

Superheat and subcooling confirm evaporator and condenser charge; target superheat sets the correct charge for fixed-orifice systems.
PT chart is embedded per refrigerant and interpolated between standard pressure points.
Gauge pressure at the suction (vapor) line service port.
Clamp thermometer reading on the suction line, insulated from the ambient.

Tip: Change any value to instantly update the result.

About this calculator

Convert gauge pressure and line temperature into superheat and subcooling using a built-in refrigerant PT chart for R-410A, R-22, R-404A, R-134a and R-454B, or confirm target superheat for fixed-orifice and TXV systems. These are the readings field technicians use to verify evaporator and condenser charge on air conditioners and refrigeration equipment. The same page covers the subcooling check and the charging chart, so searches for refrigerant charging calculator or R-410A PT chart both land here. Need a quick PT lookup? See the refrigerant PT chart below. More HVAC tools: HVAC calculators hub. Need airflow or capacity next? Use the HVAC capacity calculator or the ACH / CFM calculator.

  • Check evaporator superheat to confirm the meter is feeding the right refrigerant mass flow.
  • Check condenser subcooling to confirm the high side is fully condensed with no flash gas.
  • Set fixed-orifice target superheat from outdoor and indoor conditions before adjusting charge.
  • Compare your readings against the equipment nameplate and manufacturer charging chart.

Calculation Results

10.0°F superheat
At 120 PSIG R-410A, saturation is 55°F; a 65°F suction line gives 10.0°F superheat.
Default preview — updates when you change inputs (superheat mode).

Superheat = line temperature − saturation temperature at the measured pressure. Always confirm against the manufacturer charging chart.

Field & safety disclaimer

This calculator provides charge-screening estimates only. Refrigerant work involves high pressure and, for R-454B and blends, mild flammability and ventilation rules. For final charging, recovery, and leak checking, follow the equipment nameplate, the manufacturer charging procedure, and local code. Verify EPA Section 608 certification for anyone handling refrigerant.

Refrigerant PT Chart Quick Reference

Saturation temperature at common gauge pressures. The calculator interpolates between these points for any pressure you enter. For blends and critical charging, confirm against the manufacturer PT chart and nameplate.

Approximate saturation temperature (°F) at gauge pressure (PSIG)
PSIGR-410AR-22R-404AR-134aR-454B
60213621816
1004557234141
1406374415160
1807882496076
2409796636996
3201181207678118

Formula & How It Works

Superheat and subcooling come from the refrigerant pressure–temperature (PT) relationship: for a pure refrigerant or azeotropic blend, pressure determines the saturation temperature. Compare the measured line temperature to that saturation temperature.

Superheat

\\[ \\text{Superheat} = T_{\\text{suction line}} - T_{\\text{sat}}(P_{\\text{suction}}) \\]

Subcooling

\\[ \\text{Subcooling} = T_{\\text{sat}}(P_{\\text{liquid}}) - T_{\\text{liquid line}} \\]

Target Superheat (fixed orifice)

On a fixed-orifice system, the correct superheat rises as outdoor temperature rises and falls as indoor load rises. It is read from the equipment charging chart using outdoor dry-bulb and indoor wet-bulb. TXV/EEV systems regulate superheat themselves and are checked against a near-constant target (commonly 8–12°F).

Example: R-410A at 120 PSIG saturates near 55°F; a 65°F suction line is 10°F superheat. The same pressure on the liquid line with a 95°F liquid line would be 55 − 95 = −40°F subcooling (impossible — that reading means the probe is on the wrong line), which is why the tool separates the two modes.

Frequently Asked Questions

What is superheat?

Superheat is the number of degrees a vapor is above its saturation temperature at a given pressure. For an HVAC system it is the suction line temperature minus the refrigerant saturation temperature at the suction pressure. It confirms the evaporator is fully boiling off the liquid refrigerant before it reaches the compressor.

What is subcooling?

Subcooling is the number of degrees a liquid is below its saturation temperature at a given pressure. It is the saturation temperature at the liquid line pressure minus the actual liquid line temperature. It confirms the condenser has fully condensed the vapor and the refrigerant is free of flash gas before the metering device.

How do I calculate superheat?

Read the suction line pressure with gauges and the suction line temperature with a clamp thermometer. Look up the saturation temperature for that pressure on the refrigerant PT chart, then subtract it from the line temperature. Total superheat = line temperature minus saturation temperature.

How do I calculate subcooling?

Read the liquid line pressure and the liquid line temperature. Look up the saturation temperature at that pressure on the PT chart, then subtract the actual liquid line temperature. Subcooling = saturation temperature minus liquid line temperature.

What is normal superheat and subcooling?

Typical total superheat on a fixed-orifice (piston) system is 5-25°F depending on indoor and outdoor conditions; TXV systems hold superheat near 8-12°F. Subcooling is commonly 8-15°F on properly charged systems. Always compare against the manufacturer's charging chart for the exact unit.

What is target superheat?

Target superheat is the correct superheat a fixed-orifice system should have for the current outdoor dry-bulb and indoor wet-bulb conditions. It is read from a charging chart (often the ACCA/equipment chart using OD dry bulb and ID wet bulb). TXV systems control superheat themselves and are checked against a near-constant target.

What refrigerant PT chart does this calculator use?

The calculator embeds saturation temperature lookups for R-410A, R-22, R-404A, R-134a and R-454B, interpolated between standard published pressure points. Values are typical; always confirm against the nameplate or manufacturer PT chart for critical charging.

Why is my superheat negative?

A negative superheat means the suction line temperature is at or below saturation, so liquid or saturated vapor is reaching the compressor. This indicates overcharge, a restriction, or a metering device problem and can damage the compressor. Stop and diagnose before continuing.

Is R-454B similar to R-410A for charging?

R-454B and R-410A are both high-pressure refrigerants but R-454B has a lower saturation temperature at the same pressure and is mildly flammable (A2L). Use the R-454B PT chart in this tool and follow A2L handling and recovery rules.

Can I use this as a refrigerant charging calculator?

Yes. Enter pressure and line temperature for superheat or subcooling, or enter outdoor and indoor conditions for target superheat. The tool screens charge state; final charging must follow the equipment nameplate and manufacturer charging procedure.

Review & sources

Reviewed: CalcPanel HVAC Engineering Team

Updated: 2026-10-19

Reference