What type of equipment is used to recover refrigerant?

Refrigerant recovery machines are specifically designed to safely remove refrigerants from air conditioning and refrigeration systems. These machines are equipped with a combination of compressor systems, filters, and other components that allow for the efficient extraction and storage of refrigerants without the risk of releasing them into the atmosphere, which is crucial for environmental protection.

Using a refrigerant recovery machine ensures compliance with EPA regulations, as these regulations mandate that refrigerants must be recovered and not vented. The machine's functions typically include verifying refrigerant purity, properly handling different types of refrigerants, and managing pressures within the system.

Other options represent components related to refrigerant systems but do not serve the purpose of recovery. Refrigerant expansion valves regulate the flow of refrigerant within the system, air conditioning compressors circulate refrigerant by compressing it but do not recover it, and thermostats are used for temperature control and do not have any function related to refrigerant recovery. Therefore, the specific design and functionality of refrigerant recovery machines make them the correct choice for this question.