🔍 Key Concepts

• Compound gauge vs. absolute pressure gauge in refrigeration systems • Relationship between saturation pressure and temperature for a given refrigerant • How technicians quickly determine evaporator or condenser temperature from gauge readings

💭 Think About

• When a service technician hooks up a standard refrigeration manifold, what extra information besides pressure do they usually read directly from the gauge face? • Is the extra scale based on a fixed relationship between pressure and temperature for a given refrigerant, or does it change with superheat or subcooling? • Which of the listed temperatures (saturated, superheated, sub cooled) can be read directly from a simple gauge without doing extra calculations or using additional instruments?

✅ Before You Answer

• Verify which parameter has a direct, one‑to‑one relationship with pressure for a specific refrigerant at phase change conditions. • Check which of the temperature terms (saturated, superheated, sub cooled) describes the refrigerant exactly at boiling/condensing conditions, not above or below them. • Confirm that absolute pressure would require a different reference point (zero at a perfect vacuum) than what most compound and standard service gauges use.