In a refrigerator, what is the primary control function of the expansion (metering) valve?

Introduction / Context:
The expansion valve (capillary, thermostatic, or electronic) meters liquid refrigerant from the high-pressure condenser/liquid line into the low-pressure evaporator. It is crucial for maintaining proper evaporator feeding and pressure levels.

Given Data / Assumptions:

• Single-stage vapour-compression system.
• Condenser provides subcooled liquid to the metering device.
• Evaporator requires controlled flow to match heat load.

Concept / Approach:
The metering device creates a pressure drop from condenser pressure to evaporator pressure. It controls mass flow so that the evaporator receives the right amount of refrigerant, preventing starvation (low capacity) and flooding (risk of liquid slugging). TEVs further modulate flow to maintain a target superheat.

Step-by-Step Solution:

Verification / Alternative check:
System pressure and superheat measurements confirm correct metering: stable evaporator pressure and target outlet superheat indicate proper control.

Why Other Options Are Wrong:

Compressor start/stop, condenser pressure regulation, and non-condensable purging are separate functions handled by controls, head-pressure devices, or service procedures.

Common Pitfalls:
Misadjusting superheat on a TEV or selecting too small a capillary causing high superheat and low capacity.

Final Answer:

Correct