Chapter 9 Evaporators, Condensers, Accumulators, and Receiver-Driers 151 Copyright by Goodheart-Willcox Co., Inc. Summary Every refrigeration system has an evaporator and con- denser and every refrigeration system has either an accumu- lator or a receiver-drier. Th e evaporator and condenser work with the compressor and fl ow control device to cause the refrigerant to change state. Th e accumulator and receiver- drier store refrigerant, separate liquid and vapor refrigerant, and remove moisture. Refrigerant boils in the evaporator and absorbs heat from the air. Th ere are two refrigerant evaporator designs, the tube and fi n and the plate and fi n. Th e tube and fi n evap- orator is made from a single length of aluminum or copper tubing, folded into a series of serpentine coils. Tube and fi n evaporators can be made in any shape and size. Th e plate and fi n evaporator has less resistance to airfl ow while allow- ing more contact between refrigerant and air. Plate and fi n evaporators are roughly the same size and shape. Th e fi rst plate and fi n evaporators had the refrigerant passing in equal amounts through each fi n. Th is design caused oil to drop out of the refrigerant and an external oil return line was needed. Th e multiple-pass evaporator eliminated this problem and does not have an external oil line. Parts that may be attached to the evaporator include the expansion valve and sensing bulb, orifi ce tube, and temperature probe. All condensers are tube and fi n types, and most are cross-fl ow types with the refrigerant fl owing across the condenser. Metal fi ns are pressed over the tubing. Other condensers are header types with an inlet header that distributes refrigerant to each tube. R-134a systems use multifl ow condensers. Accumulators are located between the evaporator and the compressor inlet and store vaporized refrigerant from the evaporator. To keep liquid refrigerant from getting to the compressor, the accumulator separates liquid and vapor- ized refrigerant. A small hole at the bottom of the refriger- ant pickup tube allows oil to return to the compressor. Th e accumulator also contains the desiccant bag. Th e receiver-drier is a tank that stores condensed refrigerant and removes moisture and debris. Vaporized refrigerant rises to the top of the receiver-drier, and only liquid refrigerant exits through the bottom mounted pickup tube. Some receiver-driers have pressure switches. Th e switch turns off the compressor if the pressure goes too high. Older receiver-driers contained a pressure relief valve or a fusible plug. Th ese devices remove system pressure and prevent compressor and system damage. Pressure relief valves were installed on the compressor body of older vehicles. Pressure relief valves are no longer used. Th ey consisted of a spring-loaded valve that opened when system pressures became too high. When pressure was reduced, the valve closed. Th e fusible plug was designed to melt and blow out when system pressure and temperature became too high. Fusible plugs are no longer used since they cause the entire refrigerant charge to be lost. Review Questions—Chapter 9 Answer the following questions using the information provided in this chapter. 1. Why is an evaporator oft en called a heat exchanger? 2. What is the purpose of the rubber fl ap at the evaporator case drain? 3. Describe a multiple-pass evaporator. 4. Th e expansion valve sensing bulb is located on the _____ side of the evaporator. 5. Which of the following desiccants can be used with R-134a only? (A) XH-5. (B) XH-7. (C) XH-9. 6. _____ keep the air from bypassing the condenser. 7. Accumulators are located at what point in the refrigeration system? 8. Liquid refrigerant will fall to the _____ of the receiver-drier. 9. A high pressure switch cuts off the _____ if the pressure becomes too high. 10. Th e substance in an accumulator or receiver-drier that removes moisture from the system is called a(n) _____.