Which are the three types of recovery methods currently in use?

The correct answer identifies the three distinct methods used for refrigerant recovery during maintenance or repair of refrigeration systems. These methods include using the appliance's compressor, a designated refrigerant recovery unit, and charge migration.

Using the appliance compressor involves operating the system in reverse to recover refrigerant, allowing the existing components of the system to be utilized for effective recovery. This method is particularly beneficial when other recovery devices are not available.

The refrigerant recovery unit is a specialized device designed specifically to recover refrigerants from systems, ensuring that the process complies with environmental standards. This method is widely recognized and essential for safely removing refrigerants, especially considering the regulations surrounding the handling of ozone-depleting substances.

Charge migration refers to the movement of refrigerant within the system, typically in response to pressure changes. This method is relevant when the refrigerant can be redirected rather than forcibly extracted, leveraging the natural flow of the refrigerant.

Other listed methods, like compression, absorption, and evaporation, describe processes relevant to refrigerant management but do not directly correspond to recognized recovery methods. Similarly, options discussing liquid, gas, and solid recovery, or vaporization, condensation, and superheating focus on general physical states and thermodynamic processes rather than specific recovery techniques in refrigeration.