It is recommended that replacement of air conditioning hoses can only be done by dealer service department or in air conditioning shop only due to the dangers of depressurising the system, and disconnection of the hoses or any component must only be done only after the system is out of pressure. Rubber and plastic hoses of engine, accessory and emission systems are quite susceptible to the high temperature under the hood, so their marvelous, loose clamps, material hardness and leakage need frequent check up . Many hoses are fitted with clamps that should be checked for tension in order to exclude leakage while smooth-bore hoses without clamps must be controlled for expansion or stiffening. Blow-by gas produced in the crankcase is drained out through PCV system by a rubber hose into the intake manifold and PCV hose needs to be checked for cracks and blockage. Colour-coded vacuum hoses also exist and have certain thickness and material requirements for the walls; on replacement, vacuum hoses should be similar to the originals. It is suggested to disconnect hoses to facilitate inspection, and for rerouting purposes, they should be labeled; plastic T-fittings should be examined for cracks. A little portion of vacuum hose can be used identify if leakages are present by using a stethascope to check for hissing sounds. Fuel lines are most of the time under pressure therefore it is important that in case of leakage the fuel is collected, all rubber fuel lines should be inspected for signs of deterioration particularly at bends and at fittings. Only high quality fuel line which has been designed for the fuel-injection systems should be used for replacements, parts such as, vacuum lines that are not reinforced or plastic tubing. Screw type clamps on fuel lines should be replaced with spring-type clamps where hoses are replaced. Fuel pump to carburetor or fuel injection system steel lines must be checked to see if they have bends or cracks, the replacements must be seamless steel tubing. Brake lines especially those made of metal should also be checked for crack and loosing of fittings, any sign of brake fluid leakage should be acted on immediately. Fuel injection nylon lines used in fuel injection systems may need special material and techniques for repair while power steering hoses should be examined for leaks, loose connections and worn clamps and where there is wear, then wear part should be replaced.
