🔍 Key Concepts

• Safety procedures before opening a refrigeration system and why pressure matters • Difference between gauge pressure (psig) and absolute pressure (psia) • What condition of pressure makes it safest to open a system without drawing air/moisture in or blowing refrigerant out

💭 Think About

• Think about what happens if there is still positive pressure in the system when you loosen a flange or fitting. What will flow, and in which direction? • Consider what could happen if you pulled a vacuum or went below atmospheric pressure before opening the system. What might enter the system? • Which choice represents a condition where there is no stored energy trying to escape and minimal risk of contamination entering the system?

✅ Before You Answer

• Verify what 0 psig actually means in relation to atmospheric pressure. • Make sure you understand why refrigeration service work usually aims for no differential pressure across an opening when breaking into the system. • Confirm which option best eliminates both the risk of refrigerant discharge and the risk of drawing air or moisture into the system.