Final answer:
After 1995, supplies of CFC refrigerant in the USA for servicing existing units must come from recycled or reclaimed stocks due to the Montreal Protocol. This international agreement aims to phase out CFCs to protect the ozone layer, with replacements like HFCs and HCFCs being used instead.
Step-by-step explanation:
After 1995, any supplies of CFC refrigerant to service existing units in the USA can only come from recycled or reclaimed stocks. This is a consequence of the Montreal Protocol, an international agreement from 1987 designed to phase out substances that deplete the ozone layer, including CFCs (chlorofluorocarbons).
There has been global progress towards eliminating CFCs, with the largest contributor to CFC emissions today being China. Success in reducing CFC emissions is evidenced by signs of recovery in the ozone layer, though there are still challenges due to variability in atmospheric conditions and the existence of CFC banks from outdated equipment which can still release these harmful substances into the atmosphere.
The movement to reduce CFC usage led to the development of substitutes such as hydrofluorocarbons (HFCs) and hydrochlorofluorocarbons (HCFCs), which have a lesser impact on ozone depletion. Consequently, post-1995 refrigerant supplies for maintenance purposes in the United States must comply with these strict protocols to prevent further harm to the ozone layer.