When refrigerants are contained in a recovery cylinder, what condition must they be free from to ensure proper pressure readings?

For accurate pressure readings in a recovery cylinder, it is essential that the cylinder is free from non-condensables, such as air. Non-condensables can significantly affect pressure readings, leading to misleading assessments of the refrigerant's state. When air or other non-condensible gases are trapped in the cylinder along with the refrigerant, they do not contribute to the phase change of the refrigerant and can inflate pressure readings.

In a recovery process, the refrigerant needs to be in a purer state for effective recovery and recycling. The presence of air can lead to operational issues, such as increased system pressure and reduced efficiency. Therefore, ensuring the recovery cylinder is free from non-condensable gases allows for more precise monitoring of the refrigerant's pressure and condition.

While it is also important to consider moisture and impurities or excessive heat in the broader context of refrigerant recovery and system integrity, they do not specifically impact the accuracy of pressure readings in the same direct manner as non-condensables do. Maintaining a pure refrigerant environment enhances the recovery system's performance and reliability.