Copyright Goodheart-Willcox Co., Inc. 810 Air-Conditioning Systems This type of a preassembled refrigeration system requires careful handling, since it is charged with refriger- ant. Be careful while uncrating the tubing to avoid creat- ing kinks. The kinked areas might later crack and leak. Another type of system consists of an evaporator, con- densing unit, and line set that come as an unassembled but matched set, sized for the application. One or more of the components come precharged. The precharged com- ponents contain enough refrigerant for the entire system. The technician then connects the various components on-site. Some manufacturers provide flare fittings for con- necting the evaporator coil and compression or braze fittings for connecting the condensing unit. Other manu- facturers provide quick-connect couplings for connecting the parts. These couplers may be connected without losing refrigerant or getting air into the system. Quick-Connect Couplings Quick-connect couplings enable manufacturers to pro- duce precharged refrigeration and air-conditioning units. Necessary tubing is also provided in separate packages. These separate units can be assembled at the installation site. They are ready to operate without evacuating, charg- ing, or cleaning. Quick-connect couplings are brazed directly to the tubing. Flared joints are not needed. There are two types of quick-connect fittings: • Those that can be connected and disconnected many times with very little loss of refrigerant. When this type of coupling separates, independent springs force valves in both halves of the coupling to close. This prevents the escape of refrigerant. This type of coupling is very seldom used. • Those that can only be quick-connected once. The ends of these couplings are sealed off with diaphragms. When the two halves of the coupling are connected, the diaphragms are punctured. This allows refrigerant to pass through the coupling. See Figure 32-19. If these couplings ever need to be disconnected, the refrigerant must first be removed from the system. To assemble either type of quick-connect fitting, align the couplings and tighten the coupling nut. This draws the coupling together. Quick-connect fittings are used mostly on precharged residential air-conditioning systems. They are also used on precharged transportation units. Units are usu- ally charged at the factory. The condensing unit, refrigerant lines, and evaporator are charged separately. Figure 32-20 shows a liquid line that has an access (service) port. Access service valve Knife Diaphragms A B C Diaphragms Diaphragms folded back Rubber seal Aeroquip Corp. Figure 32-19. Quick-connect coupling equipped with a service valve. A—A knife edge aligns with and begins piercing the diaphragm. B—As the fitting is tightened, the diaphragm is punctured. C—When the diaphragm is punctured, refrigerant can flow through the coupling. The flow of refrigerant folds the remnants of the diaphragm out of the way.