Refrigerants are chemicals that absorb and release heat as they move through a cooling system to help produce air conditioning or refrigeration. They're used in air conditioners, refrigerators, freezers, chillers, and heat pumps. An HVAC system may need a recharge of refrigerants when it fails to chill or blow cold air, when ice forms on the evaporator coil, or as part of regular maintenance. Refrigerant refills are typically housed in clearly marked cylinders to avoid mixing or contamination of different refrigerants, which can cause system failures or component damage. Accessories are designed for applications such as accessing refrigerant lines, testing refrigerant samples, and locking refrigerant valves.