CHARGING • SUPERHEAT / SUBCOOLING

Superheat & Subcooling

Calculate superheat and subcooling with explicit units, optional PT-based saturation derivation, and conservative interpretation guidance. OEM procedures come first.

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PT dataset: not loaded / not available for r410a. Enter saturation temps directly.
Calculator
v1
Used for PT lookup when pressures are provided.
Used only for interpretation guidance (v1).
Hide fields you don’t need.
v1 focuses on gauge pressure for field inputs.
Superheat inputs
SH
Measured suction line temp (at proper location).
Suction saturation source
Enter evaporator saturation temperature.
v1 does not compute target superheat yet.
v1 does not compute target superheat yet.
Subcooling inputs
SC
Measured liquid line temp (at proper location).
Liquid saturation source
Enter condenser saturation temperature.
Missing/invalid inputs:
  • Enter suction line temperature.
  • Enter suction saturation temperature (or switch to pressure mode with a PT dataset).
  • Enter liquid line temperature.
  • Enter liquid saturation temperature (or switch to pressure mode with a PT dataset).
Results
Deterministic
Superheat
—°F
Suction sat: —°F • Suction line: —°F
Subcooling
—°F
Liquid sat: —°F • Liquid line: —°F
Recommendation (conservative)
  • Compare results to OEM procedures and conditions. This tool does not replace manufacturer targets.
Assumptions:
  • Saturation temps entered directly by you.
Safety note: This tool provides guidance and estimates. Always follow OEM procedures, local codes, and safe work practices.
Saved calculations
Superheat / Subcoolingtap
Saved calculations (tap to expand).
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About this calculator
REFERENCE

This calculator helps you turn your measured pressures and line temperatures into actual superheat and/or subcooling. It’s built to be fast on mobile and explicit about units and assumptions.

Who it’s for

  • Service technicians charging or verifying charge in the field.
  • Apprentices/students learning what SH/SC numbers mean.
  • Anyone who needs a quick, copy-ready summary for job notes.

When to use it

  • You’re charging or verifying charge and need actual SH/SC numbers.
  • You suspect measurement error (probe placement, unstable load) and want a quick cross-check.
  • You want a copy-ready summary for job notes (without storing customer info).

Required inputs

Refrigerant selection (so PT relationship is correct).
Required to compute results.
Suction pressure + suction line temperature (for superheat).
Required to compute results.
Head pressure + liquid line temperature (for subcooling).
Required to compute results.
Stable operating conditions (steady state) before you record readings.
Required to compute results.

Outputs

Actual superheat
Suction line temperature minus evaporator saturation temperature at the measured suction pressure.
Actual subcooling
Condenser saturation temperature at the measured head pressure minus the measured liquid line temperature.
Copy-ready summary
A short text block you can paste into job notes (inputs + outputs + units) for repeatable documentation.

How to use (field notes)

  1. Let the system stabilize (steady state) before recording readings.
  2. Clamp on clean copper, tighten the probe, and insulate it from ambient air.
  3. Double-check units (°F/°C and psig/kPa) and refrigerant selection before making adjustments.
Assumptions & limitations tap
  • Your pressure readings are gauge pressure (psig) and accurate.
  • Your clamp probe is insulated from ambient and placed on clean, solid copper contact.
  • System is at steady state (not in defrost, not rapidly staging, doors/windows not swinging load).
  • For blended refrigerants, dew/bubble can matter; the right curve depends on where you’re measuring (evap vs cond).
Safety note: Results are estimates for informational use. Always follow OEM charging procedures, safety practices, and local codes.
FAQs
DIRECT ANSWERS
Why does my superheat jump around even when the system looks stable? tap

Small errors in suction line temperature cause big swings. Make sure the clamp is tight on clean copper, insulate the probe from ambient air, and wait for steady readings. Also confirm the system isn’t staging or being hit by changing load (doors, fans, defrost, etc.).

Do I use dew or bubble for blends like R-410A? tap

In general: evaporator saturation aligns with dew and condenser saturation aligns with bubble. If your PT source provides separate curves, pick the curve that matches the measurement context and follow OEM guidance for that refrigerant/system.

Can I charge a TXV system by target superheat? tap

Usually no. TXV systems are typically charged by subcooling under specified conditions. Target superheat charts are more commonly used for fixed orifice/piston systems. Always follow the OEM method for that equipment.

What’s the fastest field check to catch a bad input? tap

Sanity-check units and ranges: psig vs psia, °F vs °C, and whether your pressures match the refrigerant and outdoor conditions. If the calculator can’t find a valid saturation point for your pressure, the input is likely out of range or the refrigerant selection is wrong.

Is 'low superheat' always flooding back? tap

Not always. Low SH can be caused by load, airflow, metering behavior, sensor placement, or transient conditions. Use SH/SC alongside airflow checks, coil condition, and OEM diagnostics before making adjustments.