Just before charging the system with clean refrigerant, you should

• A. Evacuate the system
• B. Install a new compressor
• C. Open service valves
• D. Check oil level

Answer: (A)

Evacuate the system to remove air, moisture, and non-condensables before adding refrigerant. Pulling a deep vacuum clears out ambient air and any water vapor that can form ice or acids later, which would impair lubrication, reduce heat transfer, promote corrosion, and cause improper charging. It also helps verify the system is leak-tight and ready to accept a clean refrigerant charge. Opening service valves would introduce air, installing a new compressor isn’t a pre-charge step, and simply checking oil level doesn’t prepare the system for the charge itself.