Final answer:
In MVAC system retrofitting, the replacement refrigerant must be approved by the EPA, which is responsible for regulating refrigerants to protect health and the environment.
Step-by-step explanation:
If retrofitting a MVAC system (Motor Vehicle Air Conditioning), the replacement refrigerant MUST be EPA approved. The Environmental Protection Agency (EPA) regulates refrigerants under the Clean Air Act to ensure that any substitute does not harm public health or the environment. Other organizations, like the California Air Resources Board (CARB), the Air-Conditioning, Heating, and Refrigeration Institute (AHRI), and the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) also provide standards and guidelines, but the EPA's approval is a legal requirement for refrigerants used in MVAC systems.