When servicing systems with refrigerant blends, how should charging be performed?

• A. Charged as a gas
• B. Charged as a vapor
• C. Charge in any phase
• D. Charged as a liquid

Answer: (D)

When a refrigerant blend is used, the exact mix of components matters, because different ingredients boil off at different rates. If you charge the system by introducing the refrigerant as a gas, the more volatile components tend to vaporize first and leave the others behind, changing the blend composition inside the system (fractionation). Charging in the liquid phase injects the full, correct mixture through the liquid line, helping maintain the intended ratios and ensuring the system operates with the designed performance. This approach is especially important for blends like those commonly used in modern systems; after charging, some vaporization will occur as the system runs, but the initial charge remains accurate.