If all liquid has been recovered from a system to be overhauled, what is the recommended pre-opening procedure?

• A. Should not be opened until all vapor has been recovered
• B. Open after vapor is recovered
• C. Open after depressurizing the vapor
• D. Open after flushing with nitrogen

Answer: (A)

The important rule here is to handle any remaining refrigerant vapor before you open the system. Even when all liquid refrigerant has been recovered, vapor can still be trapped under pressure inside the system. Opening the service ports while vapor is present would cause a rapid release of refrigerant, which can be dangerous to the technician (frostbite from the cold vapor, pressure-related injuries) and wasteful or environmentally harmful due to emissions.

Therefore, the safest and most reliable pre-opening procedure is to keep the system closed and complete the vapor recovery until no more vapor can be removed. Only after the vapor has been fully recovered should you proceed to open the system for overhaul. Nitrogen flushing or other methods are separate steps and do not replace the need to recover vapor first.