Vapor pressure is the pressure exerted by a vapor in equilibrium with its liquid or solid phase at a given temperature. In HVAC systems, vapor pressure determines the boiling point of refrigerants and influences system operating pressures. Every refrigerant has a unique vapor pressure curve that changes with temperature.
Refrigerant Characteristics
R-410A maintains a vapor pressure of approximately 117 PSIG at 70°F and 278 PSIG at 105°F. R-22 operates at lower pressures, around 73 PSIG at 70°F. These pressure differences require different component ratings and system designs. High vapor pressure refrigerants like R-410A allow smaller, more efficient equipment but require stronger system components rated for 400 PSIG minimum.
System Design Impact
Vapor pressure influences compressor displacement, line sizing, and component wall thickness requirements. Technicians reference pressure-temperature charts daily to verify system pressures fall within normal operating ranges, typically 100 to 300 PSIG depending on the refrigerant and ambient conditions. Abnormal vapor pressures indicate refrigerant leaks, non-condensables, or system malfunctions requiring immediate attention.