Probably, there is no such person in the world who, one way or another, faced with the installation of an air conditioner, did not wonder why only copper, and far from the cheapest pipes, are used to create a freon circuit. Why not use, for example, steel or metal-plastic, which can withstand decent pressure, are not subject to corrosion and, moreover, are much cheaper?
Reasons for using copper piping in climate technology
In fact, the reason why copper piping is used in residential air conditioning systems is quite simple: copper has a range of physical properties that neither steel, aluminum, nor most polymers have in combination.
- Copper does not interact with freon, freon and other common refrigerants.
- This material has minimal internal surface roughness. Due to this property, a high permeability of the refrigerant is ensured.
- It is resistant to temperature fluctuations.
- Copper products are known for their ductility, gas impermeability, corrosion resistance and light weight.
In fairness, it should be noted that not all air conditioning systems use copper piping. For example, in some brands of foreign cars, aluminum lines are used to move the refrigerant, which causes many problems and questions: “How to solder an aluminum air conditioner tube and why signs of oxidation appeared on it.” Whether this is due to the process of reducing the cost of production of the modern automobile industry or for ideological reasons, history is silent.
The main dimensions of the pipeline in household split systems
To combine the indoor and outdoor unit of a domestic air conditioner, pipes are used, and with different diameters: one freon is supplied in the form of a liquid, and the other passes in a gaseous state. Usually, the piping that carries the refrigerant from the evaporator to the condenser always has a larger diameter.
In climate technology, freon lines with an internal section size of 1/4 “(6.35 mm) and 3/8” (9.52 mm) are most often used. In addition to these common sizes, some split systems use a pipeline with a diameter of:
- 1/2″ (12.7 mm);
- 3/4” (19.05 mm);
- 5/8” (15.88 mm).
The main criterion when choosing these products is the performance of the air conditioner: the higher it is, the larger the diameter of the pipeline. The rate of circulation of freon in a closed circuit depends on the correctly selected diameter of the tubes for the air conditioner.
The standard wall thickness of copper piping for air conditioners usually does not exceed 0.7 mm. This is due to the fact that in the future the master will have to bend and roll the tubes, and with a larger wall thickness, it will be quite problematic to perform these works with high quality.
As a rule, most manufacturers produce copper pipes for climatic equipment already annealed, formed into coils of 15, 25 or 50 m. Annealed copper is more elastic and allows bending with little or no change in cross section.
At the ends of the pipe there must be special plugs that prevent moisture and debris from entering the product. Copper, for the pipeline of climatic equipment, can be used in different grades. The most popular is CU-DPH. Products from this brand of copper will have the highest corrosion resistance.
Despite the high resistance of copper to corrosion, there are cases of depressurization of the freon circuit, which occur due to oxidation of the main pipeline of the air conditioner. The reasons for the oxidation of the copper pipes of the air conditioner take place for several reasons, among which the main ones are:
- The negligence of some “specialists” who, when installing the air conditioner, neglect such a procedure as evacuating the system.
- Ignorance of some “repairmen” about the chemical properties of metals and fluxes.
Freon purge method
Vacuuming the circuit is a mandatory process before starting the air conditioner for the first time. This is done to remove air from the system before letting the refrigerant through it. It is this rule that is most often violated by negligent installers who do not consider it necessary to purchase expensive equipment, namely a vacuum pump and a gauge manifold. To remove air from the refrigeration circuit, such “specialists” use the method of purging the system with freon, which, by the way, is prohibited by most manufacturers of climate control equipment.
Since air conditioners are shipped partially charged with refrigerant from the factory, the purge method looks like this:
- One of the pipeline fastening nuts is released and the valve on the air conditioner opens.
- Freon must replace the air that will leave the system from under the released nut.
After such, so to speak, air removal procedures, as a rule, moisture remains on the walls of the copper pipereacts with freon, which leads to the oxidation of sections of the copper pipeline and damage to the compressor.
Galvanic couple and pitting corrosion
Now a few words about the processes occurring in metals. When some metals come into contact, microcurrents begin to flow at the place of their junction, which cause corrosion processes in a less “aggressive” metal, up to its complete destruction. When copper interacts with steel, the first metal is oxidized and the second metal is destroyed.
Imagine a situation when a compression nut (fitting) made of unalloyed steel is put on a copper pipe of a freon line. Over time, the junction oxidizes, which leads to the gradual destruction of steel and to the violation of the integrity of the oxide film that protects copper from atmospheric influences. As a result: oxidation, corrosion and depressurization of the circuit.
The table shows the galvanic compatibility of metals. The “+” sign marks materials that do not create galvanic pairs:
Situation two: the use of the wrong solder and flux for soldering the refrigeration circuit of climate technology. In fact, the proportion of such errors is 15–20% of the total number of corrosion causes. Incorrect solder can create the galvanic couple discussed above, and flux residues in pipes after soldering inevitably lead to pitting corrosion, which is characterized by a rapid flow and leads to perforation of the pipeline section.
The solution to the problem of installation and repair of the refrigeration circuit of air conditioners is seen in the use of the right materials, as well as strict adherence to the rules for connecting and soldering copper pipelines. In addition, to prevent oxidation of copper pipes and depressurization of the circuit, it is possible to “reconcile” metals that are not very “friends with each other” by the process of tinning the most “aggressive” copper.
Freon route installation
The process of installing the combination of the external and internal unit of the split system has already been described many times. I would like to dwell on only a few points that deserve special attention. The process of creating a freon line includes the correct cutting, flaring and soldering of copper tubes.
Cutting the tube into segments of a certain length is done with a tool called a pipe cutter. The use of hacksaws and other cutting tools is unacceptable. The use of a hacksaw and similar tools generates large amounts of chips that are difficult to remove from the pipeline. In addition, the use of such tools does not guarantee an even cut without nicks and burrs that will interfere with rolling. Pipes are cut with a margin of 5–10 cm, for trimming, in case of unsuccessful rolling.
Rolling is the second most important operation after cutting. The tightness of the refrigeration circuit and the durability of the air conditioner depend on the correct rolling. The tool itself looks like a clamp, in the lower part of which there are holes for pipes of different diameters.
Algorithm of actions when expanding copper pipes for an air conditioner:
- put a compression nut on the pipe section;
- insert the end of the tube into the required hole in the lower part of the self-clamping bar or vise so that it protrudes from the edge by 3–4 mm;
- by rotating the rotary mechanism in the upper part of the clamp, insert a rolling nozzle of the required size or an eccentric cone (depending on the rolling model) into the end of the tube;
- gradually turning the mechanism to disassemble the tube;
- after the end of the rolling process, release the end of the tube from the mechanism.
The flared end of the copper tube must have an ideal geometry.
As a rule, a standard air conditioning flare kit consists of a pipe cutter and a flare. Depending on the model, the rolling kit may include rolling nozzles for a 3/16″ tube diameter; 1/4″; 5/16″; 3/8″; 7/16″; 1/2″; 5/8″.
After the pipe sections are flared (neatly and correctly), they should be connected to the pipes coming out of the indoor unit. To do this, align the outlet flange with the flare nut as evenly as possible and hand-tighten the connection.
The nut is initially tightened only by hand. It should twist freely along the entire length of the thread.
After that, the nut is crimped with a wrench. Ideally, a torque wrench to control the tightening torque of the connection. If you tighten the nut tightly, the flared part of the copper tube will simply be cut off. If the nut is not tightened, refrigerant may leak out. The table of tightening torque for the connections of the copper pipes of the air conditioner is in the documents for a specific brand of climate technology. For example: for the Polaris air conditioner, the table looks like this:
If the manufacturer did not bother to publish the table, then the correct tightening can also be done “by eye”: after the nut is tightly tightened by hand, make another ¾ turn with a wrench.
Refrigeration circuit repair
Most often, air conditioning pipes require repair due to refrigerant leaks in the system. Repair of the pipeline consists in identifying the place of leakage, cutting out the leaking section of the pipe, followed by building up the pipeline and soldering it.
- After cutting the pipeline, its ends must be prepared: one end must be flared with a flaring nozzle so that the ends of the pipeline can be inserted into each other.
- After that, the surface of the inner tube should be cleaned of patina with fine sandpaper or abrasive paste and inserted into each other.
- [>The next step is the heating of the pipeline section at a distance of 6–10 cm from the junction. Warming up is carried out to such a state until the solder melts upon contact with the junction.
Only copper-phosphorus or copper-silver solder can be used for soldering
- Pour solder over the joint, evenly distributing it around the entire perimeter of the joint.
Installation and connection of the freon route of the air conditioner, in principle, can be done independently. The durability of your split system depends on the correct installation and quality of work. Entrust this work to professionals.