Free Tool
Superheat & Subcooling Calculator
Enter your gauge and temperature readings to instantly calculate superheat and subcooling. Supports R-410A, R-22, R-134a, R-404A, R-407C, R-32, and R-454B. Works on your phone in the field.
Suction Side
Superheat Calculator
Actual suction temp minus saturation temp at suction pressure
Liquid Side
Subcooling Calculator
Saturation temp at liquid pressure minus actual liquid line temp
What Is Superheat & Subcooling?
Superheat
Superheat is the number of degrees a vapor refrigerant has been heated above its saturation (boiling) temperature at a given pressure. It is measured at the suction line and tells you how much refrigerant vapor has been fully vaporized in the evaporator. A properly charged system will show 10–20°F of superheat at the suction service valve for most fixed-metering systems.
Formula: Superheat = Suction line temp − Saturation temp at suction pressure
Subcooling
Subcooling is the number of degrees a liquid refrigerant has been cooled below its saturation (condensing) temperature at a given pressure. It is measured at the liquid line and confirms that refrigerant is fully condensed and free of flash gas before it reaches the metering device. Most residential and light commercial systems target 10–15°F of subcooling.
Formula: Subcooling = Saturation temp at liquid pressure − Liquid line temp
Target Ranges by System Type
These are general guidelines. Always confirm with the manufacturer's installation manual — target ranges can vary based on outdoor ambient temperature and system design.
| System Type | Target Superheat | Target Subcooling |
|---|---|---|
| Residential split — fixed metering (piston/orifice) | 10–20°F | 10–15°F |
| Residential split — TXV/TEV metering device | 8–12°F | 10–15°F |
| Light commercial package unit | 10–18°F | 10–15°F |
| Heat pump (cooling mode) | 10–15°F | 10–15°F |
| Commercial refrigeration (medium-temp) | 8–15°F | 8–12°F |
Key Facts for HVAC Technicians
A superheat reading below 5°F on the suction line indicates a risk of liquid refrigerant reaching the compressor, which can cause compressor damage or failure.
A superheat reading above 20°F combined with low suction pressure is one of the most reliable indicators of a refrigerant undercharge or a restricted metering device.
Subcooling below 5°F at the liquid line typically means refrigerant is not fully condensed — the metering device may be receiving flash gas, reducing system capacity significantly.
For R-410A systems, saturation temperature at a typical suction pressure of 120 psig is approximately 40°F. A suction line temperature of 55°F at that pressure gives a superheat of 15°F — within the normal range.
For R-22 systems, saturation temperature at 68 psig is approximately 40°F. Because R-22 operates at lower pressures than R-410A, technicians need refrigerant-specific PT data to avoid misdiagnosis.
Frequently Asked Questions
What is normal superheat for a residential system?
For most residential split systems with a fixed metering device (piston or orifice), target superheat is typically 10–20°F measured at the suction service valve. Systems with a thermostatic expansion valve (TXV or TEV) should be closer to 8–12°F at the evaporator outlet. Always consult the manufacturer's data plate — some systems specify a narrower target range based on outdoor ambient and indoor wet-bulb temperature.
What causes high subcooling?
High subcooling (above 20°F) typically indicates an overcharge of refrigerant, a restriction in the liquid line (such as a clogged filter-drier or a kinked line set), or condenser fan motor issues that prevent proper heat rejection. A liquid line restriction will also show high subcooling on the upstream (condenser) side combined with a noticeable temperature drop across the restriction point.
How do I measure suction line temperature correctly?
Use a clamp-style temperature probe (type K thermocouple or similar) on the suction line approximately 6 inches from the service valve on the outdoor unit. Insulate the probe with a small piece of foam insulation tape to prevent the ambient air temperature from affecting the reading. Avoid measuring at elbows or at brazed joints. Let the system run for at least 15 minutes before taking readings to allow conditions to stabilize.
What tools do I need to measure superheat and subcooling?
You need a digital manifold gauge set to read suction and discharge (liquid) pressures in psig, a clamp-type temperature probe or digital thermometer to measure line temperatures, and a PT chart or this calculator to convert pressure to saturation temperature. Many modern digital manifolds calculate superheat and subcooling automatically once you select the refrigerant — but this calculator lets you verify those readings independently.
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Researched by the RefrigerantTrack Research Team