R-438A (MO99) Pressure at 140°F — Saturation P-T Data
How This Was Calculated
Saturation pressure interpolated from ASHRAE tabular data for R438A. Elevated pressure — high-side normal range.
- P_sat
- Saturation pressure: 315 PSI
- T_input
- Input temperature: 140°F
- T_data
- ASHRAE tabular reference data: R438A
Important Considerations
At 140°F, R438A is at 315 PSI — in the elevated range above 300 PSI. This is within normal high-side operating conditions for hot weather but warrants attention. Confirm condenser coil is clean, fans are operating, and ambient temperature is within equipment rated limits. Monitor for pressure trending higher over a season, which may indicate refrigerant overcharge or coil fouling.
140°F is an extreme operating temperature — above the rated ambient limit for most residential HVAC equipment (typically 115–120°F). At this condition, R438A reaches very high saturation pressure which stresses compressor windings and discharge valves. Most manufacturers void warranty for operation above rated ambient. Consider condenser shading, pre-cooling, or equipment with expanded ambient ratings for installations in direct sun in hot climates.
The saturation pressure shown (for R438A at 140°F) is the baseline for measuring superheat and subcooling. Suction superheat = suction line temperature minus evaporator saturation temperature. Subcooling = condensing saturation temperature minus liquid line temperature. Typical targets: 8–12°F superheat at the evaporator (TXV systems), 10–20°F subcooling at the condenser. Deviations indicate improper charge, metering device issues, or non-condensables.
R438A — consult ASHRAE Standard 34 and manufacturer safety data sheet for handling requirements. EPA Section 608 certification is required for purchase and handling.
R438A has a GWP of 2,265 — meaning 1 lb released equals 2,265 lbs of CO2 equivalent warming over 100 years. This places it in the high-GWP category subject to accelerated phase-down under the AIM Act (American Innovation and Manufacturing Act). EPA regulations are reducing HFC production and import allowances through 2036. Lower-GWP alternatives are available: R-32 (GWP 675), R-454B (GWP 466), and R-290 (GWP 3) depending on application.
Saturation pressure-temperature data for R438A 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.