AC pipes route refrigerant between the compressor, condenser, and evaporator inside the engine bay. They are made of aluminum because it is light, rejects heat, and handles high pressure. Rubber sections are crimped in where the pipes connect to the vibrating engine to prevent cracking.
These lines carry refrigerant at pressures up to 350 PSI. If a pipe rubs against a metal bracket, it can wear a pinhole. This leak releases refrigerant gas and PAG oil, disabling the A/C system.
Replacing an AC pipe requires evacuating the system with a recovery machine. Once unbolted, you must replace the rubber O-rings at the connections. Pulling a vacuum is required to remove moisture before recharging the system.