Final answer:
Supplies of a phased-out refrigerant come from recycled or reclaimed stocks following international agreements like the Montreal Protocol.
Step-by-step explanation:
After a refrigerant is phased out, supplies of that refrigerant for equipment servicing can only come from recycled or reclaimed stocks. When international environmental legislation like the Montreal Protocol mandates the phase-out of a particular refrigerant, such as chlorofluorocarbons (CFCs), production of new supplies ceases.
Consequently, any necessary servicing of equipment that still uses these refrigerants must rely on existing supplies that have been recovered from other systems, and then recycled or chemically reclaimed to ensure that they meet industry standards for reuse. This process helps to protect the environment and the ozone layer by reducing further emissions of harmful substances.