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TM 5-4120-287-15 Section II.  REFRIGERANT TUBING SERVICE 7-11.  General a. This section describes the methods used to clean and replace the refrigerant carrying tubing in the air conditioner. b. The maintenance area should be equipped with such standard items of equipment as suitable air and electrical outlets and work benches.  It is important that the maintenance area be clean and dust-free.  Keep hardware and small parts together in trays to prevent them from being mislaid. Cover parts which are to stand for any period of time with clean paper or suitable coverings. c. Discard all lockwashers, tab lockwashers, preformed packings, and composition gaskets as they are removed. When removing preformed packings, be careful not to damage the preformed packings cavities and/or adjacent surfaces involved in sealing. 7-12.  Maintenance of Refrigerant System in Air Conditioning Unit The refrigerant system piping must be absolutely clean and the joints properly connected in order to eliminate contamination or leakage of the refrigerant. a. Keep all tubing sealed.  When a refrigerant line is disconnected, seal it immediately with masking tape or plug it depending on the type of connection. b. Keep all installation and servicing tools, test gauges, and replacement parts clean. c. Do not keep the air conditioning unit open longer than necessary.  When a system must be opened, the servicing tools and other equipment must be ready for use so that minimum time is required to perform the operation. 7-13.  Refrigerant Tubing a. General.  Copper tubing is utilized to carry the refrigerant through the vapor cycle system (fig. 1-11 and 7-3).  The wall thickness of the copper tubing, depending on the required refrigerant pressure and capacity in a particular copper tube air conditioner operation, ranges from 0.030 inches to 0.050 inches. b. Fittings.  Brazed fittings (sweated joints) are used at tube junctions to assure against the possibility of refrigerant leakage. 7-14.  Brazed Connections a. Opening a Brazed Joint.  When opening a brazed joint perform the following steps: (1)   Discharge and purge the refrigerant from the air conditioner (para 7-7 and 7-8).  Purge the area around the joint with nitrogen to assure that any refrigerant due to leakage has been expelled from the area. (2)   Using an oxy-acetylene torch, heat the joint beyond the melting point of the filler material. (3)   Using well-insulated gloves, and/or other appropriate hand tools separate the joined tubes before the filler material temperature drops below the melting point. CAUTION Using masking tape or plugs, immediately seal any lines opened to the atmosphere.  This is requisite for preventing moisture and/or dirt from entering the vapor cycle system - b. Joining Brazed Fittings. (1)   Braze fittings in accordance with Military Specification MIL-B-7883. (2)   Use class 4 or 6A silver solder filler material as designated in QQ-S-561d. 7-15.  Flared Joints a. General.  The compressor discharge assembly with a flared end, mates with a fitting machined to accommodate an 0 ring when the coupling nut on the tube assembly is threaded on to the fitting.  The combination of the mating flares and the compressed 0 ring ensure a leak proof connection (fig. 7-4).  The filter-drier SAE flared nuts do not require an O-ring. NOTE New 0 rings are required every time a flared tube assembly is removed and rejoined. b. Torque Requirements.  When installing tube assemblies it is essential that the coupling nut be tightened to the torque requirements shown in table 1-1, torque requirements. 7-6

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