Cooling and air-conditioning installations utilize the change of cooling agent parameters (pressure, temperature and state) when it circulates between the evaporator and the condenser in the cooling system. The cooling agent circulates driven by the refrigerating compressor. The refrigerant absorbs heat by evaporation in the evaporator, then it gives up heat when vapour is condensed in the condenser. There are many types of refrigerants (water, carbon dioxide, ammonia), however there is one special type of low-boiling hydrocarbons, called freons.
Flexible freon hoses are widely used in air-conditioning systems of various vehicles (cars, machinery, trains, trams) as well as in smaller installations of industrial cooling. In these installations, freon (e.g. R134a, R1234yf) mixed with compressor oil (e.g. PAG synthetic oil) acts as a refrigerant. It circulates in the system where it undergoes continuous pressure and temperature fluctuations. Therefore, requirements concerning freon hoses are so high. It is essential for the system to be perfectly tight as freon is very penetrating, expensive and harmful to the environment. It must be highly resistant to pressure, temperature, chemicals and stop humidity from permeating the hose wall. It concerns automotive air-conditioning in particular because there, the freon hose operates in the engine compartment, tightly packed and bent, in high ambient temperature conditions, exposed to vibrations and in contact with car fluids.
The air-conditioning hoses, including those intended for cars are mounted with special types of fittings, often dedicated to one make or type of vehicle. For hoses for industrial air-conditioning, see also the group: steel hoses.