HVAC & Refrigeration Pressure Conversion: PSIG to PSIA & Gauge Readings
HVAC pressure guide for converting manifold gauge readings: 0 PSIG, 15 PSIG, 250 PSIG to PSIA. Formulas for subcooling, superheat, and vacuum.
Mastering HVAC refrigeration pressure conversion from PSIG to PSIA is essential for reading pressure-temperature (P-T) charts, calculating superheat and subcooling, and verifying vacuum evacuation levels. HVAC/R technicians rely on manifold gauge readings to measure high-side liquid line and low-side suction line pressures in PSIG.
For quick online HVAC gauge conversions, use our PSIG to PSIA converter on the home page.
1. HVAC Pressure Regimes: PSIG vs PSIA in Heating & Cooling
- Deep Vacuum Evacuation: Measured from 0 PSIG down to -14.7 PSIG ($14.7\text{ PSIA}$ to $0\text{ PSIA}$). Technicians target micron levels (e.g., 500 microns) relative to absolute zero.
- Low-Side Suction Line: Operates around 10 PSIG to 30 PSIG for low-temperature refrigeration or 118 PSIG for R-410A air conditioning.
- High-Side Liquid Line: Operates around 250 PSIG to 400 PSIG for high-pressure refrigerants like R-410A.
Read our detailed breakdown on PSIG vs PSIA difference explained.
2. Converting HVAC Refrigeration Pressure: PSIG to PSIA Formula
To look up saturation temperatures on absolute thermodynamic tables, convert manifold PSIG to PSIA:
$$\text{PSIA} = \text{PSIG} + 14.7$$
To convert back from thermodynamic tables to manifold gauges:
$$\text{PSIG} = \text{PSIA} - 14.7$$
Quick answer: HVAC Refrigeration Pressure Conversion
Answer: In HVAC refrigeration systems, 0 PSIG equals 14.7 PSIA. 15 PSIG equals 29.7 PSIA. 250 PSIG equals 250 PSI gauge and 264.7 PSIA absolute.
3. HVAC Refrigerant Pressure Conversion Table & Benchmarks
| Refrigerant State | Gauge Reading (PSIG) | Gauge PSI | Absolute Pressure (PSIA) |
|---|---|---|---|
| Deep Vacuum (Atmospheric) | 0 PSIG | 0 PSI | 14.7 PSIA |
| R-134a Suction Line | 15 PSIG | 15 PSI | 29.7 PSIA |
| R-22 Low-Side Suction | 60 PSIG | 60 PSI | 74.7 PSIA |
| R-410A Low-Side Suction | 118 PSIG | 118 PSI | 132.7 PSIA |
| R-134a High-Side Line | 150 PSIG | 150 PSI | 164.7 PSIA |
| R-410A High-Side Line | 250 PSIG | 250 PSI | 264.7 PSIA |
4. Key Calculation Benchmarks for HVAC Technicians
- 0 PSIG to PSIA: $0 + 14.7 = 14.7\text{ PSIA}$.
- 15 PSIG to PSIA: $15 + 14.7 = 29.7\text{ PSIA}$.
- 250 PSIG to PSI: $250\text{ PSIG} = 250\text{ PSI gauge}$.
- 250 PSIG to PSIA: $250 + 14.7 = 264.7\text{ PSIA}$.
For reverse conversions, read how to convert PSIA to PSIG and how to convert PSIG to PSIA.
Use our free online PSIG to PSIA calculator anytime.
Related Resources
- PSIG to PSIA Tool: Homepage PSIG to PSIA Calculator – Online unit converter engine.
- PSIG to PSIA Guide: How to Convert PSIG to PSIA – Detailed formula & calculation guide.
- PSIA to PSIG Guide: How to Convert PSIA to PSIG – Reverse conversion calculations.
- Compressed Air Systems: Compressed Air System Pressure Guide – Pneumatic tool & compressor conversion.
Frequently asked questions
Why do HVAC manifold gauges read in PSIG?
HVAC digital and analog manifold gauges measure refrigerant pressure relative to atmospheric air, displaying readings in PSIG.
How do you convert 0 PSIG to PSIA in HVAC vacuum testing?
0 PSIG on an HVAC manifold equals 14.7 PSIA at sea level. Below 0 PSIG indicates vacuum evacuation (measured in microns or inches of Hg).
How do you convert 250 PSIG to PSI / PSIA for R-410A refrigerant?
250 PSIG equals 250 PSI gauge pressure, and 264.7 PSIA absolute pressure at standard sea level (250 + 14.7 = 264.7 PSIA).