Which unit is commonly used to specify a refrigerant charge for small systems?

• A. Gallons
• B. Kilograms
• C. Liters
• D. Pounds

Answer: (D)

In small HVAC/R systems, refrigerant charge is specified by weight. This is because the exact amount of refrigerant that actually fills and circulates in the system is best determined by mass, not volume. You can accurately control and verify the charge by weighing the refrigerant cylinder before and after charging, ensuring the system gets the designed mass of refrigerant.

Volume measures like gallons or liters aren’t reliable for this purpose since refrigerant density changes with temperature and pressure, and different refrigerants have different densities. Kilograms are a metric mass unit, but the common practice in the U.S. for small systems is to use pounds, aligning with how cylinders are labeled and how service procedures are carried out. Using pounds helps technicians achieve the correct charge, which is essential for proper pressure, efficiency, and system protection.