Answer :
Final answer:
In a refrigeration system using R-11, a vapor pressure of 15 psig is necessary before charging with liquid. The correct option is D. 15 psig.
Explanation:
In this case, a vapor pressure of 15 psi (pounds per square inch gauge) is necessary for the shells before changing with liquid. This pressure is required for the proper functioning of the refrigeration system. When recharging a refrigeration system with R-11, the necessary vapor pressure in the shells before changing with the liquid is 1 psig. This ensures that non-condensable gases are purged out and that the system is not contaminated. The process requires careful monitoring of pressure to avoid any potential issues that could arise from incorrect charging.