The major components of an air conditioning system all have an inlet and outlet connection. It's the refrigerant lines that connect these parts together allowing them to function as one. O-ring seals are provided at the various connections providing a tight seal while allowing for some flexibility to absorb vibration and movement. This design also facilitates the replacement of individual pieces.

All automotive AC will have at least three major refrigerant lines. These include the suction hose, liquid line and the discharge. The suction hoses are located between the outlet side of the AC evaporator and the inlet side of the compressor. It's referred to as the suction side because this is where the compressor uses vacuum to pull in refrigerant. These are low pressure hoses that should be cool to the touch when operating and larger in diameter than the others found throughout the system.

The discharge line connects from the outlet of the compressor and runs to the inlet of the AC condenser located out in front of the radiator. This can cover a lot of ground on some automobiles and therefore is often the longest. The liquid line connects the condenser outlet to the receiver drier also known as the accumulator on some applications. This is the only line that is carrying Freon in the liquid state hence its nickname.

Discharge and liquid lines are always very warm to the touch and easily distinguishable from the much larger diameter suction line. Both of these high pressure hoses are made up mostly of aluminum tubing but can contain small sections of rubber hose to allow for flexibility and safe routing in the engine compartment. Any rubber hose utilized in an air conditioning system is specially manufactured to carry refrigerant. Vehicles that use the R134A type of Freon have an additional layer of rubber that serves as a barrier to prevent the refrigerant from escaping through the pores of the hose.