Naming pressures in a refrigeration compressor What is the standard term for the pressure measured at the inlet of a refrigerant compressor (i.e., the evaporator pressure at the suction line)?

Introduction / Context:
Correct terminology helps in reading P–h charts, service gauges, and troubleshooting logs. The compressor has a low-pressure side (suction) and a high-pressure side (discharge).

Given Data / Assumptions:

• Standard vapour-compression layout with evaporator, compressor, condenser, and expansion device.
• Inlet line to compressor originates from evaporator outlet/suction accumulator.

Concept / Approach:
The pressure at the compressor inlet is called suction pressure. It corresponds to the evaporating pressure and is read on the low-side gauge in service practice. Some texts also refer to evaporator pressure as back pressure; however, “suction pressure” is the unambiguous term at the compressor inlet.

Step-by-Step Solution:
Identify component: compressor inlet.Associate pressure name: suction pressure (low side).Note: discharge pressure is the high-side pressure at compressor outlet; critical pressure refers to fluid property, not line pressure.

Verification / Alternative check:
Service manifolds label LP gauge for suction (evaporator) pressure and HP gauge for discharge (condensing) pressure.

Why Other Options Are Wrong:

• Discharge pressure: outlet, not inlet.
• Critical pressure: property at critical point, unrelated to component location.
• Back pressure: sometimes synonymous with evaporator pressure, but the standard inlet term is suction pressure.

Common Pitfalls:
Using “back pressure” interchangeably can cause confusion in multi-stage or cascade systems.

Final Answer:
Suction pressure