If suction superheat is lower than recommended, the most likely reason is:

• A. Too much refrigerant in the evaporator
• B. Too little refrigerant in the evaporator
• C. Impaired capillary tube
• D. Dirty condenser coils

Answer: (A)

Suction superheat shows how completely the evaporator turns liquid refrigerant into vapor before it reaches the compressor. When suction superheat is lower than recommended, it usually means the evaporator is flooded with liquid refrigerant—there’s too much refrigerant in the evaporator and not enough of it is vaporizing before leaving. Because a larger portion of the refrigerant remains liquid, the vapor that does reach the suction line is cooler and closer to the evaporator’s saturation temperature, so the measured superheat is lower.

If there were too little refrigerant in the evaporator, you’d typically see higher superheat, since the vapor leaving would be more vapor-heavy and at a higher temperature relative to the evaporator pressure. A restricted capillary tube or dirty condenser coils can affect pressures and flow, but they don’t explain a lower suction superheat as consistently as an overfilled evaporator.