When oil has been removed from a compressor, it should be tested for _________________________.

Testing oil that has been removed from a compressor for acidity and contamination is critical for several reasons. Acidity in oil can indicate the presence of harmful breakdown products that can lead to corrosion and increased wear on engine components. Tracking acidity levels helps assess the oil's degradation and its ability to lubricate effectively.

Contamination is equally important. Oil can become contaminated with particulate matter, water, or other fluids, which can compromise its lubricating properties and cause damage to the compressor's internal components. Identifying the type and extent of contamination allows for corrective measures to be taken, such as filtering or replacing the oil, ensuring the longevity and reliability of the compressor.

In contrast, moisture and pressure, temperature and flow rate, as well as viscosity and density are also important parameters in different contexts but do not specifically address the key factors affecting oil quality and performance after removal from a compressor. Focusing on acidity and contamination gives a more direct insight into the operational health of the system.