AC Superheat Calculator Simple & Advanced Modes

Enter suction pressure and line temperature to get Actual Superheat. In Advanced mode, add indoor wet-bulb and outdoor temperature for a Target Superheat and charge guidance (best for fixed-orifice systems).

Superheat Calculator

Results are estimates. Always follow manufacturer data and local regulations.

Refrigerant

Temperature

Pressure

Superheat — At a Glance

Refrigerant: — Units: — Suction Ps: — Suction Line T: — Indoor WB: — Outdoor DB: — Metering: —

Live snapshot of the latest inputs above (Simple or Advanced mode).

What is Superheat and Why It Matters

Superheat (SH)

Actual SH = suction line temperature − saturation temp (from suction pressure via PT table). It confirms the refrigerant is fully boiled to vapor before the compressor, preventing liquid floodback.

Target vs. Actua
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For fixed-orifice/piston systems, you charge to a Target SH (depends on indoor wet-bulb & outdoor dry-bulb). For TXV/EEV, the valve controls SH (typical 8–12°F at evap outlet), so you generally charge by subcooling per OEM.

How to Take Accurate Readings

Run system 10–15 minutes to reach steady state. Filters clean, coil clean, doors/windows typical use.
Clamp a thermocouple on the insulated suction line 6–12″ from the service valve; insulate the probe.
Read suction pressure at the low-side port (psig/kPa).
Measure Indoor Wet-Bulb at the return (psychrometer) and Outdoor Dry-Bulb near the condenser (shade).
Use the calculator: get Actual SH. If fixed orifice, compute Target SH and compare.

Airflow matters: aim for ~35

0–450 CFM per ton. Low airflow raises SH and lowers SC, confusing charge decisions.

Interpreting Superheat

Actual SH High

Likely undercharge, low indoor load, or low airflow.
Check filter, blower speed, coil cleanliness, return restrictions.
If airflow normal → add charge toward target (fixed orifice).

Actual SH Low

Risk of floodback (liquid to compressor).
Could be overcharge, high indoor load, or TXV bulb/insulation issue.
Verify subcooling & TXV sensing bulb placement/tightness.

On Target

Charge likely correct for current conditions.
Cross-check with subcooling and OEM data plate.
Re-verify after airflow adjustments.

Common Pitfalls to Avoid

Reading WB at a supply grille (should be at the return).
Not insulating the suction temperature clamp—sun/wind skew readings.
Adjusting charge before confirming airflow & coil/filter condition.
Comparing to target SH on a TXV system (use subcooling instead).

Frequently Asked Questions

What is the difference between superheat and subcooling?

Superheat is sensible heat added to vapor after it boils. Subcooling is sensible heat removed from liquid below its saturation temp. Charge fixed orifice by superheat; charge TXV systems by subcooling (OEM).

When should I use Target Superheat?

Use Target SH for fixed-orifice systems. It varies with indoor WB and outdoor DB. Our advanced mode estimates target so you can compare to Actual SH and adjust charge accordingly.

What superheat is normal for TXV/EEV?

Typically ~8–12°F at the evaporator outlet under normal load. If far outside this range, check the sensing bulb, airflow, and charge.

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My Actual SH is much higher than Target — what now?

First verify airflow (filters/blower/coil). If airflow is correct, a significantly high SH suggests undercharge or low indoor load. Add charge in small steps and recheck.

Can I use °C and kPa?

Yes. The calculator supports °F/°C and psi/kPa. Superheat itself is a temperature difference; we display delta in °F for consistency.

How accurate is the Target SH formula?

It’s a field-tested approximation to OEM charts that tracks well in typical comfort cooling. For brand-specific charging, always defer to the manufacturer’s target tables.