Type III EPA 608 Certification Practice Exam

The correct vapor pressure for charging a refrigeration system with liquid R-11 is 16.9 inches of mercury (Hg) vacuum. This value is significant because it correlates with the saturation pressure of R-11 at a specific low temperature, allowing for efficient liquid transfer into the system.

R-11 is a chlorofluorocarbon (CFC) refrigerant that is often utilized in low-pressure refrigeration applications. To effectively charge a system with R-11, the refrigerant must be in a liquid state, which necessitates that the pressure inside the charging system be adequately low to draw the refrigerant from the storage tank.

A vapor pressure of 16.9 inches of Hg vacuum corresponds to approximately 10°F (or -12°C) which is well aligned with the operating characteristics of R-11. This vacuum level assists in ensuring that the refrigerant remains stable and can readily flow into the system without encountering issues such as vapor lock or inefficiencies.

Undertaking a charge at a lower vapor pressure such as 20.5 or 10.0 Hg vacuum may not provide sufficient driving force for the liquid to enter the system, while a 5.0 Hg vacuum is too high for R-11 to remain in