R-717 (Ammonia) Pressure at 75°F — Saturation P-T Data
How This Was Calculated
Saturation pressure interpolated from ASHRAE tabular data for R717. Normal operating pressure range.
- P_sat
- Saturation pressure: 282 PSI
- T_input
- Input temperature: 75°F
- T_data
- ASHRAE tabular reference data: R717
Important Considerations
This is the saturation pressure for R717 at exactly 75°F (23.9°C). If your gauge reads significantly different from 281.7 PSI with a confirmed stable system temperature, suspect a faulty gauge, partial blockage, or mixed/contaminated refrigerant.
The 75°F saturation temperature is what the refrigerant thermodynamically wants to be at 281.7 PSI — not what the pipe surface reads. Measure the pipe surface temperature and compare to 75°F to calculate superheat (suction line) or subcooling (liquid line). The difference tells you whether the system is properly charged.
Saturation pressure-temperature data for R717 derived from ASHRAE Fundamentals Handbook, Chapter 30 (Thermophysical Properties of Refrigerants), and verified against manufacturer published data (Chemours Opteon, Honeywell Solstice). Values represent saturated conditions at sea level.
Understanding R717 at 75°F / 281.7 PSI
At 75°F (23.9°C), R717 saturates at 281.7 PSI. That reading tells you the system state and which side it applies to — within limits. Below: how to use it, and what it cannot tell you.
What this reading tells you about system state
281.7 PSI at 75°F means the refrigerant is at its saturation point — it exists as a liquid-vapor mixture at this exact pressure and temperature combination. At 75°F saturation, identify which side of the system this gauge is connected to before interpreting the result — suction and discharge saturation temperatures have different normal ranges.
Suction side vs liquid side — why saturation temp differs
In a properly operating system, suction saturation temperature (evaporator) and liquid saturation temperature (condenser) are different by design. R717 suction saturation in a cooling application typically runs 35–50°F; liquid saturation typically runs 100–120°F on a hot day. The compressor maintains the pressure difference between them. Reading 281.7 PSI — at 75°F, this reading is outside the typical range for both sides — verify which service port you are connected to.
Three things this P-T lookup can't tell you
This chart gives you the saturation pressure for a pure R717 sample at 75°F. It cannot tell you: (1) whether the refrigerant in the system is actually pure R717 or a contaminated blend — use a refrigerant identifier if you suspect mixing; (2) whether there is non-condensable gas (air, nitrogen) in the system pushing pressures artificially high; (3) whether the system is over- or undercharged — charge diagnosis requires superheat and subcooling measurements alongside this pressure reading.
Why using the wrong refrigerant's P-T table is a critical error
If the system contains R-410A but you reference the R-22 chart, you will calculate a completely wrong saturation temperature from the same pressure. R-410A at 130 PSI saturates at approximately 45°F; R-22 at 130 PSI saturates at approximately 100°F — a 55°F difference. Always confirm the refrigerant type on the equipment nameplate before referencing any P-T chart. If the nameplate is illegible or missing, use a refrigerant identifier before proceeding.
Common Mistakes with R717 P-T Readings
- Confusing gauge pressure (PSIG) with absolute pressure (PSIA). P-T charts use gauge PSI. Absolute pressure adds 14.7 PSI to gauge readings. Most field manifold gauges read PSIG — which is what you want. If you are using a chart or app that specifies PSIA, subtract 14.7 before looking up the temperature. At 281.7 PSIG, the absolute pressure is 296.4 PSIA.
- Reading across to the wrong refrigerant column on a multi-gas chart. At 281.7 PSI, saturation temperatures differ by 50°F or more between refrigerant types. Always locate the R717 column first, then read the temperature. Misreading a neighboring column produces a valid-looking number that is completely wrong for the system you are servicing.
- Diagnosing charge from pressure alone. A reading of 281.7 PSI confirms that saturation temperature is 75°F — nothing more. Proper charge diagnosis requires comparing saturation temperature to pipe surface temperature (superheat on the suction side, subcooling on the liquid side). Pressure alone cannot tell you if the system is properly charged, overcharged, or undercharged.
- Not accounting for non-condensable contamination. If measured pressure is consistently higher than the expected P-T value at the measured pipe temperature, suspect air or nitrogen in the system. Non-condensables raise discharge pressure and reduce efficiency without changing refrigerant type. This will make the system appear overcharged on a pressure check. Recover and recharge to confirm.