1. FIGURE 7-1 Air is circulated through the A/C and heating system and the car to either add or remove heat. (Courtesy of Toyota Motor Sales USA, Inc.)

2. FIGURE 7-2 Automotive A/C systems are either a TXV system with a receiver–drier (a) or an OT system with an accumulator (b). Various compressors are used with both systems. (Courtesy of Visteon)

3. FIGURE 7-3 The high and low sides of an A/C system are divided by the compressor (where the pressure is increased) and either a TXV or an OT (where the pressure drops).

4. FIGURE 7-4 Refrigerant changes state to a vapor as it absorbs heat in the low side and into a liquid as it loses heat in the high side.

5. FIGURE 7-5 As liquid refrigerant enters the evaporator, the boiling point will try to drop as low as 32°F because of the drop in pressure. The cold temperature causes the refrigerant to absorb heat from the air circulated through the evaporator.

6. FIGURE 7-6 If the proper amount of refrigerant enters the evaporator, it has a slight superheat as it leaves (a). A starved condition, in which not enough refrigerant enters the evaporator, does not produce as much cooling (b). If too much refrigerant enters, the evaporator floods because the refrigerant will not all boil (c).

7. FIGURE 7-7 The low side begins at the TXV or OT and includes the evaporator and suction line to the compressor (a). The OT system includes an accumulator (b).

8. FIGURE 7-8 A TXV is controlled by the pressure on the diaphragm from the heat-sensing tube, the pressure spring, and evaporator pressure through the equalizer pipe (a). An H-type valve is essentially the same except evaporator pressure goes through an internal passage to the bottom of the diaphragm (b). (a. Courtesy of Toyota Motor Sales USA, Inc; b. Courtesy of Chrysler LLC )

9. FIGURE 7-9 Some systems use a suction throttling valve to keep evaporator pressure from dropping to the point at which icing can occur.

10. FIGURE 7-10 An OT is a simple restriction that limits the flow of refrigerant into the evaporator. The locating dimple keeps the OT from moving downstream.

11. FIGURE 7-11 Two views of a typical OT system; (a) is somewhat realistic and (b) is schematic. Both show the arrangement of the components and the refrigerant flow. (Courtesy of ACDelco)

12. FIGURE 7-12 A tube-and-fin (a) and a plate (b) evaporator
FIGURE 7-12 A tube-and-fin (a) and a plate (b) evaporator. Each type has a large contact area for heat to leave the air and enter the refrigerant.

13. FIGURE 7-13 Accumulators are designed so that vapor from the top leaves to the compressor. They contain desiccant to absorb water from the refrigerant and many include a fitting for low-side pressure and the clutch cycling switch.

14. FIGURE 7-14 Water in an A/C system can combine with refrigerant to form acids. These acids can etch and dissolve components, cause rusting of metal parts, and cause ice blockage at the expansion device.

15. FIGURE 7-15 An automotive A/C system has the potential to lose refrigerant through hoses ,the compressor shaft seal, and line fittings.( Courtesy of Everco Industries)

16. FIGURE 7-16 A system with the proper charge has the receiver–drier (a) or the accumulator (b) about half full of liquid.( Courtesy of Everco Industries)

17. FIGURE 7-17 A properly charged system has the condenser filled with condensing vapor and some liquid, a liquid line filled with liquid, a receiver–drier about half full of liquid, and an evaporator with vaporizing liquid (a). An overcharge with too much liquid causes liquid to partially fill the condenser (b). An undercharge has vapor in the liquid line and a starved evaporator (c).

18. FIGURE 7-18 The compressor clutch allows us to cycle the compressor off and on to control evaporator temperature and to shut the system off. (Courtesy of Everco Industries)

19. FIGURE 7-19 Most TXV systems use a thermal switch to cycle the compressor out when the evaporator gets too cold (a). Most OT systems use a pressure switch to cycle the compressor out when the low-side pressure drops too low (b).

20. FIGURE 7-20 A suction throttling valve (STV) stops evaporator pressure from dropping below 30 psi, and this keeps ice from forming on the evaporator.

21. FIGURE 7-21 A hot gas bypass system diverts high-side pressure into the evaporator to keep the pressure from dropping to the point at which icing can occur.

22. FIGURE 7-22 When the evaporator cools and low-side pressure drops, the piston stroke of a variable displacement compressor is reduced so that compressor output matches the cooling load. (Reprinted with permission of General Motors Corporation)

23. FIGURE 7-23 Piston compressors can drive the piston through a crankshaft (a), Scotch yoke (b), swash plate (c), or wobble plate (d). A rotary compressor can use vanes (e) or a pair of scrolls (f). (a and e are courtesy of Toyota Motor Sales USA, Inc.; c and d are courtesy of Zexel USA Corporation)

24. FIGURE 7-23 (CONTINUED) Piston compressors can drive the piston through a crankshaft (a), Scotch yoke (b), swash plate (c), or wobble plate (d). A rotary compressor can use vanes (e) or a pair of scrolls (f). (a and e are courtesy of Toyota Motor Sales USA, Inc.; c and d are courtesy of Zexel USA Corporation)

25. FIGURE 7-23 (CONTINUED) Piston compressors can drive the piston through a crankshaft (a), Scotch yoke (b), swash plate (c), or wobble plate (d). A rotary compressor can use vanes (e) or a pair of scrolls (f). (a and e are courtesy of Toyota Motor Sales USA, Inc.; c and d are courtesy of Zexel USA Corporation)

26. FIGURE 7-24 As the piston moves downward in the cylinder, evaporator pressure opens the suction reed and fills the cylinder with refrigerant (a). As the piston moves upward, piston pressure forces the discharge reed open and the refrigerant into the high side (b).

27. FIGURE 7-25 As the rotor turns in a clockwise direction, the vanes move in and out to follow the contour of the housing. This action forms chambers that get larger at the suction ports and smaller at the discharge ports. Evaporator pressure fills the chambers as they get bigger, and the reducing size forces the refrigerant into the high side. (Courtesy of Zexel USA Corporation)

28. FIGURE 7-26 This through-vane compressor has vanes that contact the rotor housing at each end, and they slide to make a seal at each end as the rotor turns. The vanes form a pumping chamber that gets larger at the suction port and smaller at the discharge port. (Courtesy of Toyota Motor Sales USA, Inc.)

29. FIGURE 7-27 A cutaway view of a scroll compressor
FIGURE 7-27 A cutaway view of a scroll compressor. Note that one scroll is secured to the housing and the other can be moved through its orbit by the drive shaft. (Courtesy of Sanden International)

30. FIGURE 7-28 As the orbital scroll moves, it forms pumping chambers/ gas pockets that start at the suction ports and force the refrigerant to the discharge port at the center. (Courtesy of Chrysler LLC)

31. FIGURE 7-29 This electric scroll compressor (a) is operated by a DC electric motor operating off batteries. A similar compressor can be used in a heat pump (b). Note that the heat pump is very similar to an A/C system that includes a reversing valve that can swap the high and low sides. (a is courtesy of Sanden International)

32. FIGURE 7-30 A condenser is a heat exchanger that transfers heat from the refrigerant to the air flowing through it.

33. FIGURE 7-31 A tube-and-fin condenser is made up of a series of fins with the tubes passing through them. An extruded tube condenser uses flat tubes with the fins attached between them. Flat tube condensers can use either parallel or serpentine flow. (Courtesy of Four Seasons)

34. FIGURE 7-32 The refrigerant follows a winding path through a serpentine condenser (top); it follows a back-and-forth path through a parallel-flow condenser (bottom).

35. FIGURE 7-33 The volume of gas that enters a condenser is about 1,000 times the volume of liquid leaving it.

36. FIGURE 7-34 A dual condenser: the refrigerant flows from the condenser portion through the modulator/receiver–drier portion and then through the subcooling portion.

37. FIGURE 7-35 The outlet of a receiver–drier is close to the bottom so liquid flows on to the TXV. Many units include a sight glass so we can observe this flow. (Courtesy of Toyota Motor Sales USA, Inc.)

38. FIGURE 7-36 A high-pressure relief valve (a) contains a strong spring that keeps the valve closed unless high-side pressure (from the left) forces it open; the valve can close when the pressure drops. The fusible plug (b) contains a meltable metal insert that will blow out if pressure gets too high.

39. FIGURE 7-37 A refrigerant hose contains one or two reinforcing braid layers around the rubber tube (a). A barrier hose includes an impervious nylon layer to reduce leakage (b). (Courtesy of Veyance Technologies, Inc.)

40. FIGURE 7-38 The three major hoses/lines are the discharge, liquid, and suction lines. Many systems have two liquid lines.

41. FIGURE 7-39 Most systems use three of these four refrigerant hose sizes. (Courtesy of Four Seasons)

42. FIGURE 7-40 Various fittings are used to seal the refrigerant line connections. The service fitting is used for metal line repairs or to insert an inline filter.

43. FIGURE 7-41 Spring-lock and quick-connect couplers are merely pushed together, and a garter spring or plastic cage keeps them coupled.

44. FIGURE 7-42 A double-wall heat exchanger is a tube within a tube; the inner tube is convoluted so it won’t kink as the tubing is bent.