Which type of recovery machine is used to recover refrigerant from the system without utilizing the system compressor?

A self-contained recovery machine is designed specifically to recover refrigerant without relying on the system's compressor. This type of machine includes its own refrigeration loop and compressor. It operates independently, allowing for efficient recovery of refrigerants directly from the system, ensuring that the refrigerant is taken out and stored immediately, which is essential for both safety and environmental regulations.

Portable machines, while effective for refrigerant recovery, typically require the option of connecting to the system’s compressor or use another method for flow, which does not fit the criteria of recovering refrigerant independently. Centrifugal machines are typically used for air conditioning systems but do not fit the context of refrigerant recovery directly from systems. Vacuum pumps, on the other hand, are used primarily to remove moisture and air from a system, rather than recovering refrigerant directly.

The self-contained recovery machine is the best choice for this scenario, as it fulfills the requirement of independent operation from the system's compressor, ensuring a streamlined refrigerant recovery process.