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About This Tool
The HVAC Refrigerant PT Chart, Superheat & Subcooling Calculator helps service technicians and HVAC installers verify refrigerant charge levels across split systems, heat pumps, and refrigeration units.
How the Diagnostic Works: You select the system refrigerant (R-410A, R-134a, R-32, R-22, or R-404A) and input measured gauge pressures and pipe temperatures from your manifold gauges and thermocouple clamps. The calculator determines saturation temperatures from pressure-temperature polynomial fits, then computes superheat and subcooling deltas: • Superheat (°F) = Suction Line Temperature - Evaporator Saturation Temperature • Subcooling (°F) = Condenser Saturation Temperature - Liquid Line Temperature
Charge Diagnostics: • Normal Operation: Target superheat between 8°F and 18°F and target subcooling between 8°F and 14°F indicate balanced TXV metering and proper refrigerant volume. • Undercharged / Leak: High superheat (>18°F) paired with low subcooling (<6°F) indicates insufficient refrigerant mass flow. • Overcharged: Low superheat (<5°F) paired with high subcooling (>15°F) indicates excess refrigerant backing up into the condenser, posing compressor floodback risks. • Liquid Line Restriction: High superheat paired with high subcooling indicates a plugged filter drier or stuck thermostatic expansion valve.
Worked Example: An R-410A split system with 118 PSI suction pressure has an evaporator saturation temperature of 40°F. If the physical suction line temperature measures 55°F, superheat is 15°F (55°F - 40°F). With 335 PSI liquid pressure (104°F condensing saturation) and a 95°F liquid line temperature, subcooling is 9°F (104°F - 95°F), confirming normal operating charge.
Execution & Privacy: All pressure-temperature conversions and diagnostic delta calculations evaluate locally in your web browser. No service records or system readings are saved or transmitted to any server.
How to Use
- 1
Select your system refrigerant type (R-410A, R-134a, R-32, R-22, or R-404A).
- 2
Enter suction low-side gauge pressure in PSI and measured suction line temperature in °F.
- 3
Enter liquid high-side gauge pressure in PSI and measured liquid line temperature in °F.
- 4
Review the calculated evaporator and condenser saturation temperatures, superheat delta, subcooling delta, and operational diagnostic message.
Frequently Asked Questions
Why is superheat measured on systems with fixed orifices and subcooling on TXVs?
Fixed-orifice metering devices cannot adjust flow dynamically, making suction superheat the primary indicator of evaporator charge. Thermal expansion valves (TXVs) regulate superheat automatically, making liquid line subcooling the primary indicator of condenser charge volume.
What causes both high superheat and high subcooling simultaneously?
High superheat paired with high subcooling typically indicates a liquid line restriction, such as a clogged filter drier, kinked liquid line, or partially stuck TXV restricting refrigerant flow to the evaporator while backing up liquid in the condenser.
How does gauge pressure relate to refrigerant saturation temperature?
Refrigerants change state between liquid and vapor at specific saturation temperatures determined by pressure. The PT chart provides the exact boiling or condensing temperature corresponding to a measured manifold gauge pressure.
Does this calculator transmit gauge readings over the internet?
No. All thermodynamic saturation equations and differential calculations run strictly in your web browser.