Air conditioning systems use refrigerants and a vapor-compression cycle to cool air for personnel comfort, preserving perishable items, and keeping equipment operating. There are different types including industrial, residential, and personnel air conditioners. Key components are the compressor, condenser, coils, refrigerant, expansion valve, and evaporator coils. Heat is transported by the refrigerant between coils that either absorb or remove heat from the air or refrigerant.