Which of the following can be used to flush a system after refrigerant recovery?

Flushing a refrigeration system after refrigerant recovery is an essential maintenance task that helps to remove any contaminants, moisture, and debris that may be present. Nitrogen is the preferred choice for this process due to its inert properties and ability to effectively purge the system without causing any chemical reactions or introducing moisture.

Using nitrogen under pressure allows technicians to displace the remaining refrigerant and contaminants within the system's components, such as lines, coils, and filters, ensuring a clean environment for the new refrigerant to operate efficiently. Additionally, nitrogen is a dry gas, significantly reducing the risk of moisture contamination, which can lead to issues like refrigerant breakdown and corrosion within the system.

The other options present various risks and limitations that make them unsuitable for flushing a refrigeration system. R-22, a refrigerant, is not appropriate to use for flushing since it can leave residues and is regulated for environmental concerns. Compressed air can introduce moisture and oil into the system, potentially causing damage. Water is not suitable due to its ability to introduce contaminants and promote corrosion within the components, especially in systems that depend on refrigerant to function properly.

Using nitrogen helps ensure that the system is thoroughly cleaned and primed for optimal performance with the new refrigerant.