🔍 Key Concepts

• Difference between high-pressure, medium-pressure, and low-pressure refrigerants • Typical operating evaporator pressures for common refrigerants like R-12, R-22, R-123, R-134A • Which refrigerants are commonly used in centrifugal chillers and large AC plants

💭 Think About

• Think about which refrigerant is associated with large chiller systems that operate below atmospheric pressure on the low side. • Recall which of these refrigerants are generally considered high-pressure and used in smaller direct expansion (DX) systems. • Ask yourself: on an exam, which refrigerant is most commonly identified as a low-pressure refrigerant in safety and maintenance questions?

✅ Before You Answer

• Identify which refrigerant typically has evaporator pressures below atmospheric pressure at normal chilled-water temperatures. • Separate the choices into high-pressure vs low-pressure based on their common use in marine and industrial HVAC systems. • Verify in your reference materials which refrigerant is linked with centrifugal chiller / low-pressure system safety procedures (leak tests, purge units, etc.).