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.

  1. Cop­per does not inter­act with fre­on, fre­on and oth­er com­mon refrig­er­ants.
  2. This mate­r­i­al has min­i­mal inter­nal sur­face rough­ness. Due to this prop­er­ty, a high per­me­abil­i­ty of the refrig­er­ant is ensured.
  3. It is resis­tant to tem­per­a­ture fluc­tu­a­tions.
  4. 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.Variety of pipeline sizes

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.Annealed Copper Pipe

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:

  1. The neg­li­gence of some “spe­cial­ists” who, when installing the air con­di­tion­er, neglect such a pro­ce­dure as evac­u­at­ing the sys­tem.
  2. 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:

  1. One of the pipeline fas­ten­ing nuts is released and the valve on the air con­di­tion­er opens.
  2. 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.Consequences of exposure to oxidation

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:Galvanic compatibility of metals

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.Pipe rolling machine

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.

Rolling resultAs 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:Torque table

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.

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