When a recip compressor's discharge line is cool, it could indicate:

When the discharge line of a reciprocating compressor is cool, it usually indicates that the system is not operating correctly, potentially due to problems in the evaporator. If the evaporator coils have frozen, the refrigerant flow can be impeded, leading to reduced heat exchange. This can result in lower temperatures in the discharge line as the compressor is pumping refrigerant that hasn't absorbed sufficient heat, making it feel cooler than expected.

This situation can occur because ice formation in the evaporator restricts airflow or refrigerant flow, creating poor heating conditions within the system. Consequently, the compressor may be discharging refrigerant that has not adequately converted the absorbed heat, leading to cooler temperatures in the discharge line.

Understanding this phenomenon helps in diagnosing issues within the refrigeration cycle and is crucial in ensuring the efficient operation of the system.