A/C Hoses, Lines And Fittings
Refrigerant is routed to the various components in the AC system by rigid lines and flexible high-pressure hoses. Hoses are used to connect components with the compressor, to allow for engine movement. Most other components are connected with rigid lines, although hoses are sometimes used. Most modern hoses are made of reinforced rubber with a nylon inner layer as a barrier material to prevent refrigerant leakage. Most lines are made of aluminum. Generally, the line or hose of largest diameter is the one between the evaporator and compressor on the low side of the system. The smaller diameter lines connect the compressor to the condenser and the condenser to the evaporator on the high side. Often there is a muffler between the compressor and condenser to quiet the pumping noise of the compressor. Inspect the refrigerant lines and hoses for leaks, kinks, dents and any other damage. Damaged lines and hoses are usually replaced, but in some cases they can be repaired. The fittings and crimping tool equipment used by some shops to custom make hoses can also be used to repair an existing hose. Rigid lines can be repaired by cutting out the damaged section of tubing. A new section is then installed and connected to the existing line using special collars that are crimped on.
When installing a new hose or line, make sure it is routed properly and that all guides and retainers are in place, if equipped. Do not replace a line or hose with one that is longer or shorter than the original, as damage from vibration or interference with other components may result. Hoses and lines are connected to components and one another using several types of fittings, including 0-ring fittings, manifold fittings and spring lock fittings. Most all fittings use 0-rings at the attachment ends. 0-rings should be replaced each time a connection is disturbed and lubricated with refrigerant oil before installation. Replacement 0-rings must also be selected with refrigerant compatibility in mind.
Spring Lock Fittings
Spring lock fittings require a special tool to disconnect them. To disconnect a spring lock fitting, first properly recover the refrigerant from the system, then fit the tool over the fitting. Push the tool into the cage opening to release the female fitting from the garter spring, then pull the male and female fittings apart. Remove the tool from the fitting. Remove and discard the 0-rings, being careful not to scratch the tubing. Inspect the garter spring and remove it if broken or damaged. Clean the ends of the fittings. Install a new garter spring, if removed. Lubricate new 0-rings with clean refrigerant oil and install them. Lubricate the fitting ends with clean refrigerant oil, then push them together with a slight twisting motion. The fitting is properly connected if the garter spring is over the flared end of the female fitting. Evacuate and recharge the system, then check for leaks.
Service Port Fittings
As described earlier, service valve fittings are unique to the type of refrigerant originally fitted to the system. The high and low-side fittings are different to prevent connecting service hoses to the wrong fittings. The reason for the different fitting designs is to prevent cross contamination of systems, refrigerant supplies, and service equipment. The fittings are covered with caps also containing o-rings. Always re-install the caps after service, and replace any damaged 0-rings in the caps. A worn Schrader valve core in a service port fitting is often the cause of a refrigerant leak. After recovering the refrigerant, the valve core can be removed using a valve core removal tool. Lubricate the new core with refrigerant oil and install it finger tight. Evacuate and recharge the system, then check for leaks
Although not usually installed as original equipment, many vehicle manufacturers recommend installation of in-line filters in a system that has suffered a compressor failure. The main reason is for protection of the new compressor from metal chips or other debris that could be in the system from the original compressor failure. The other reason is that the debris could also clog orifice tube or expansion valve filters, or wedge in an expansion valve and keep it from operating properly. There are filters that fit into both the high and low sides of the system.
The condenser is a heat exchanger much like a radiator. In fact, it is usually located just in front of the radiator on most vehicles. Air flow across the condenser is provided by an engine driven or electric motor operated fan, and at higher road speeds, by ram air. The hot, vaporized refrigerant is pumped from the compressor into the condenser. As the refrigerant winds its way through the condenser coils, it loses much of its heat to the surrounding air through its tubes and fins. As it cools, the high pressure vapor condenses into a warm, high pressure liquid. There are three basic types of condensers: tube and fin, serpentine, and parallel flow. The tube and fin style has pipes that pass through fins, with U-shaped fittings on the ends of the pipes connecting one to the next. The serpentine condenser has a flat, continuous piece of tubing that snakes through the fins. This type is more efficient than the tube and fin design, and it’s more compact. The parallel flow condenser is most similar to a radiator in its construction and is the most efficient of the designs in terms of heat transfer. Condenser replacement is required if the unit leaks or if it is damaged or clogged. Suspect a defective condenser if high-side pressures are excessive or if there has been a compressor failure and debris is suspected to be clogging the condenser. A restriction in the condenser is indicated by frost forming near the condenser outlet. Frost can also form on the condenser itself at the point of restriction in the condenser.
To replace a condenser, first recover the refrigerant from the system. Disconnect the negative battery cable and remove any components necessary to gain access to the condenser. Disconnect the refrigerant lines from the condenser and cap the lines to prevent system contamination. Remove the fasteners that secure the condenser and remove the condenser from the vehicle. Measure the amount of oil found in the condenser that was removed, and then add the same amount of fresh refrigerant oil into the replacement condenser. If oil has leaked out of the system, use the manufacturer’s recommended amount. Position the condenser in the vehicle and install the mounting fasteners. Tighten all fasteners to specifications. Using new lubricated 0-rings, connect the refrigerant lines. Install any components that were removed for condenser access. Reconnect the negative battery cable. Next, evacuate and recharge the NC system and check for leaks. Finally, check system performance.
As its name implies, the receiver/drier stores and dries the refrigerant. More accurately, a desiccant inside of it absorbs moisture from refrigerant. Receiver/driers are only used on systems that use expansion valves. They are located between the condenser and evaporator in the high pressure side of the system, ahead of the expansion valve. Inside the receiver/drier housing is a filter, a bag of desiccant (drying agent) and a pickup tube. If the air conditioning system has a sight glass, it is often located on the top of the receiver/drier. In its ‘receiver’ function, the unit stores liquid refrigerant until the evaporator needs it. How long and how much refrigerant is stored depends on cooling demand. On hot, humid days, demand is high and refrigerant isn’t stored long.
In its ‘drier’ function, the receiver/drier protects the rest of the system from the damaging effects of moisture. Water in the system can combine with refrigerant and lubricant, form corrosive substances, and even change the chemical composition of refrigerant and lubricant. The desiccant, which usually looks like very large granules of salt, is contained within a porous bag. This bag sometimes breaks, which allows the desiccant to leave the receiver/drier and Bow throughout the system. This obviously renders it ineffective as a moisture absorbent. The desiccant can only absorb and hold so much moisture. If too much water gets in the system, the desiccant must be replaced. In most cases, you have to replace the whole receiver/drier unit to achieve this. Desiccants are not universal. Different types must often be used with different refrigerants and lubricating oils.
The receiver/drier should be replaced if it leaks, if it is clogged, if the system has been left open for a period of time or if major system service has been performed, such as compressor replacement. Suspect a defective receiver/drier if desiccant is found in other parts of the system, if there is moisture or debris in the system, or if there is a significant temperature difference in the liquid line before and after the receiver/drier or there is frost on the receiver/drier, which would indicate a restriction.
To replace a receiver/drier, first recover the refrigerant from the system. Disconnect the negative battery cable and disconnect any electrical connectors from the receiver/drier. Remove any components necessary to gain access to the unit. Disconnect the refrigerant lines from the receiver/drier and cap the lines to prevent system contamination. Remove the fasteners that secure the receiver/drier and remove it from the vehicle. If equipped, remove any switches or sensors that are mounted on the receiver/drier. If necessary, install any switches or sensors that were removed onto the replacement receiver/drier. Measure the amount of oil found in the receiver/drier that was removed, and then add the same amount of fresh refrigerant oil into the replacement receiver/drier. If oil has leaked out of the system, use the manufacturer’s recommended amount. Position the receiver/ drier in the vehicle and install the mounting fasteners. Tighten all fasteners to specifications. Using new, lubricated 0-rings, connect the refrigerant lines. Install any components that were removed for receiver/drier access. Reconnect the electrical connectors to the receiver/ drier, if necessary, and reconnect the negative battery cable. Next, evacuate and recharge the A/C system and check for leaks. Finally, check system performance.