What is the abnormal suction pressure reading for the low stage compressor?

A suction pressure reading that is significantly lower than the normal operating range for a low-stage compressor indicates an abnormal condition. In industrial refrigeration, low-stage compressors typically operate at certain pressure ranges depending on the system design and refrigerant used.

The selection of 9 inches of mercury (HG) as an abnormal reading suggests that it falls below what is typically expected for low-stage compressors under regular operating conditions. Abnormal suction pressures can indicate several issues such as low refrigerant levels, restrictions in the suction line, compressor malfunction, or even heat exchanger inefficiencies.

It's important to consider that normal operating ranges may vary based on specific system designs. However, in many cases, readings significantly below the manufacturer's specified parameters could point towards potential problems, requiring investigation and corrective actions to maintain system efficiency and prevent damage to the compressor.