Superheat & Subcooling Calculator — Diagnose Refrigerant Charge in Seconds

How It Works

1. Select Your Refrigerant

   Choose the refrigerant type from the dropdown. The calculator uses refrigerant-specific saturation temperature tables to convert pressures to temperatures. Using the wrong refrigerant will give incorrect saturation temperatures and invalid superheat/subcooling readings.

2. Enter Suction Pressure and Temperature

   Measure suction pressure at the service valve on the suction line and suction line temperature with a clamp thermocouple 4-6 inches from the compressor. Enter both values. The calculator determines the saturation temperature from the pressure and subtracts it from the line temperature to get actual superheat.

3. Enter Liquid Pressure and Temperature

   Measure liquid (discharge/high side) pressure at the liquid line service valve and liquid line temperature with a clamp thermocouple near the condenser outlet. The calculator converts pressure to saturation temperature and subtracts the line temperature from saturation to get subcooling.

4. Enter Ambient Conditions for Target Superheat

   For fixed-orifice systems, enter outdoor ambient temperature and indoor wet-bulb temperature. The calculator uses the standard charging chart to determine the target superheat for your conditions. TXV systems do not require this step since subcooling is the primary charge indicator.

5. Review Diagnostic Results

   Compare actual superheat and subcooling against targets. High superheat with low subcooling usually indicates undercharge. Low superheat with high subcooling usually indicates overcharge. The calculator flags out-of-range values and suggests probable causes including charge level, metering device, and airflow issues.

Built For

• HVAC service technicians checking refrigerant charge on residential split systems and heat pumps during maintenance calls
• Refrigeration mechanics diagnosing charge issues on walk-in coolers, reach-in freezers, and commercial refrigeration systems
• HVAC apprentices learning to interpret superheat and subcooling readings in the field with instant feedback
• Commercial HVAC technicians verifying charge on rooftop units and packaged systems after coil cleaning or compressor replacement
• Heat pump technicians checking charge in both heating and cooling modes with mode-specific target values
• HVAC instructors demonstrating the relationship between pressure, temperature, and charge level in training environments

Features & Capabilities

Multi-Refrigerant Support

Built-in saturation tables for R-410A, R-22, R-134a, R-404A, R-407C, R-32, and other common HVAC and refrigeration refrigerants. Select your refrigerant and the calculator handles the pressure-to-temperature conversion automatically.

Target Superheat Calculator

Uses the standard charging chart method to calculate target superheat for fixed-orifice (piston/capillary tube) systems based on outdoor ambient temperature and indoor wet-bulb temperature. Shows the acceptable range so you know if the system is within spec.

Diagnostic Interpretation

Flags high or low readings and suggests probable causes. High superheat with low subcooling points to undercharge or restriction. Low superheat with normal subcooling points to airflow problems. The diagnostic logic covers the most common field scenarios.

TXV vs Fixed-Orifice Mode

Separate diagnostic paths for TXV and fixed-orifice systems. TXV systems use subcooling as the primary charge indicator. Fixed-orifice systems use the target superheat method. The calculator adjusts its recommendations based on the metering device type.

Saturation Temperature Display

Shows the calculated saturation temperatures for both suction and liquid sides so you can verify the conversion against your gauge manifold or refrigerant PT chart. Transparency in the calculation helps catch input errors.

PDF Export

Export your readings and diagnostic results as a branded PDF for customer records, warranty documentation, or training portfolios. The export includes all inputs, calculated values, and diagnostic notes.

Frequently Asked Questions