Before opening the compressor crankcase to take an oil sample, you should

• A. Valve off the compressor and recover the refrigerant down to 1-2 psig
• B. Fully evacuate the system to 0 psig
• C. Increase the system pressure to 50 psig
• D. Loosen the crankcase bolt while running

Answer: (A)

The main idea is to safely isolate the crankcase and bring the refrigerant pressure down before opening it to sample the oil. You do this by valveing off the compressor and recovering refrigerant until the pressure inside the crankcase is about 1–2 psig. At that near-ambient pressure, removing the crankcase plug won’t cause a loud flare of refrigerant or oil, and it minimizes the chance of releasing refrigerant to the atmosphere or drawing in moisture and contaminants. It keeps the operation controlled and safe.

Evacuating the system to 0 psig would create a vacuum and isn’t necessary or desirable for a simple oil sample; increasing the system pressure to 50 psig would keep the area highly pressurized and dangerous to open; loosening the crankcase bolt while the compressor is running could spurts oil and refrigerant and risk injury.