Why does low refrigerant cause coils to freeze?

Low refrigerant causes evaporator coils to freeze through a fundamental principle of thermodynamics involving pressure and boiling point relationships inside a closed loop. Refrigerant is designed to absorb heat as it changes from a liquid to a gas under specific low-pressure conditions inside the indoor evaporator coil. When a system has a refrigerant leak, the total volume of circulating fluid drops, which ironically causes the operating pressure inside the coil to decrease significantly below normal levels. According to physical gas laws, a drastic drop in pressure causes a corresponding drop in the boiling point temperature of the remaining refrigerant. Instead of boiling at a safe 40 degrees Fahrenheit to absorb heat comfortably, the refrigerant inside the coil drops to well below 32 degrees Fahrenheit. As a result, the metal surface of the coil becomes freezing cold, causing any moisture naturally present in the household air passing over it to instantly condense and freeze into a solid layer of frost and ice.