RACA Journal February 2025 RACA_February2025 | Page 43

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• Unprofessional installations may lead to fretting , chaffing and movement of wires against tubing and damage the copper tubes , leading to refrigerant leakages and consequently system failure

• The arrangement of system components and valves within the refrigerant circuit should also be considered as they may be exposed to high pressures , temperatures and vibrations

As installation and assembly are among the main tasks , best practice procedures are necessary for efficient quality of installation , servicing and maintenance .

There are other aspects which we may consider , for example the simple Schrader valve cap . Schrader valves are commonly used for refrigerant circuit connections with service gauge manifolds or direct connections to control devices . For general system servicing they play an important role . A Schrader valve ( without a sealing cap ) is not leak-proof !

Several types of sealing caps are used in practice :

• Knurled sealing cap with elastomer / rubber seal . Over time the elastomer / rubber seal of the knurled sealing cap ages and begins leaking . In addition , they become porous or get damaged by mechanical influences . If system components , compressors , condensers , evaporators , refrigerant transfer pipes have Schrader valves with knurled sealing caps these should be replaced by a hexagon cap nut or a flare nut with copper seal .

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• With regard to the hexagon cap with conic sealing surface and the flare nut with copper seal , when tightening the hexagon cap take care to ensure that the Schrader valve body is secured with a spanner . Tightening torque of 14 to 18 Nm applies ; use of a torque wrench is considered best practice . The sealing face of the copper seal should not be coated with oil . The smallest amounts of oil can cause copper seals to leak .

Kusaan , you may encounter a hexagon cap with rubber / elastomer seal . As with the knurled sealing cap it is not recommended as the tightening torque is not specified , damage to the seal poses an additional issue .

In the case of domestic refrigeration fridges , it is best practice to pinch the process tube and remove the Schrader valve .

Looking at the refrigerant tubing itself , as the world implements natural environmental refrigerants we should revisit refrigerant copper tubing . Copper is an excellent material for use with refrigeration and air conditioning systems . With decreasing temperature copper offers increasing stability and expansion . Brittleness with low temperatures does not exist compared to other materials , such as steel . Copper pipes are resistant against reactions with all refrigerants except ammonia ( NH3 ). As we implement newer refrigerants there have been changes to copper tubing specifications and one should ensure that the correct grade of tubing is used for a specific refrigerant . Good examples of this are copper tubing used with CO2 and R410a .

Requirements and conditions specified for copper pipes are referring to :

• Refrigerant tubing must be seamless

• Quality of the inner surface

• Closed ( caps ) pipe ends / dehydrated

• Marking of the pipes

• Stability against pressure

The term ‘ temper ’ describes the strength and hardness of the tube . In the pipe trades , drawn temper tube is often referred to as hard drawn tube and annealed as soft drawn tube .

Soft , annealed copper tubing is far more versatile than rigid copper tubing . It can be purchased in much longer lengths , is rolled up and requires fewer joints which reduces leak potential . Due to its fairly flexible nature , it can be positioned and shaped easily , which saves installation time . Soft drawn tube can be commonly joined by the use of flare-type joints . It is also possible to expand the end of one tube so that it can be joined to another by brazing , a procedure that can be efficient and economical in many installations ( swaged joints ).

Nevertheless , mechanical connections should be reduced in favour of brazed joints . Copper tube for RAC field service is designated by actual outside diameter . Soft drawn tubing typically ranges from 6.35mm to 22.2mm in size

Hard drawn copper pipes are rigid , and this type of piping makes a neater installation , but it is more time consuming and more difficult to install than soft tubing . It needs little mechanical support to keep it in position , compared to soft copper .

Rigid copper tube is generally joined by brazing , using capillary fittings or by welding and with the use of compression fittings . Hard drawn tubing is available in larger sizes than soft drawn tubing . Sizes range from 6.35mm to 104.78mm .

Lastly , if possible , formed pieces ( hand bent fitting pieces ) that can be prepared on site using a mechanical pipe bender are preferred . If fittings cannot be avoided the tubing should be laid out to use a minimum number of fittings . Long radius elbows should generally be used with refrigeration tubing . A long radius elbow has a longer sweep and will have less pressure drop than a short radius elbow . Only use a short radius elbow if it is absolutely necessary for clearance considerations .

Kusaan , I hope that this helps with your understanding around ensuring system tightness and reducing , or even eliminating refrigerant leaks . RACA

REFERENCES : 1 . ACRA 2 . GIZ Proklima