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.)
Automotive Heating and Air Conditioning, Fifth Edition
By Tom Birch
© 2010 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
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)
Automotive Heating and Air Conditioning, Fifth Edition
By Tom Birch
© 2010 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
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).
Automotive Heating and Air Conditioning, Fifth Edition
By Tom Birch
© 2010 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
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.
Automotive Heating and Air Conditioning, Fifth Edition
By Tom Birch
© 2010 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
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.
Automotive Heating and Air Conditioning, Fifth Edition
By Tom Birch
© 2010 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
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).
Automotive Heating and Air Conditioning, Fifth Edition
By Tom Birch
© 2010 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
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).
Automotive Heating and Air Conditioning, Fifth Edition
By Tom Birch
© 2010 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
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 )
Automotive Heating and Air Conditioning, Fifth Edition
By Tom Birch
© 2010 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
FIGURE 7-9 Some systems use a suction throttling valve to keep evaporator pressure from dropping to the point at which icing
can occur.
Automotive Heating and Air Conditioning, Fifth Edition
By Tom Birch
© 2010 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
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.
Automotive Heating and Air Conditioning, Fifth Edition
By Tom Birch
© 2010 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
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)
Automotive Heating and Air Conditioning, Fifth Edition
By Tom Birch
© 2010 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
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.
Automotive Heating and Air Conditioning, Fifth Edition
By Tom Birch
© 2010 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
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.
Automotive Heating and Air Conditioning, Fifth Edition
By Tom Birch
© 2010 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
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.
Automotive Heating and Air Conditioning, Fifth Edition
By Tom Birch
© 2010 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
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)
Automotive Heating and Air Conditioning, Fifth Edition
By Tom Birch
© 2010 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
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)
Automotive Heating and Air Conditioning, Fifth Edition
By Tom Birch
© 2010 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
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).
Automotive Heating and Air Conditioning, Fifth Edition
By Tom Birch
© 2010 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
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)
Automotive Heating and Air Conditioning, Fifth Edition
By Tom Birch
© 2010 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
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).
Automotive Heating and Air Conditioning, Fifth Edition
By Tom Birch
© 2010 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
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.
Automotive Heating and Air Conditioning, Fifth Edition
By Tom Birch
© 2010 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
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.
Automotive Heating and Air Conditioning, Fifth Edition
By Tom Birch
© 2010 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
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)
Automotive Heating and Air Conditioning, Fifth Edition
By Tom Birch
© 2010 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
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)
Automotive Heating and Air Conditioning, Fifth Edition
By Tom Birch
© 2010 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
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)
Automotive Heating and Air Conditioning, Fifth Edition
By Tom Birch
© 2010 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
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)
Automotive Heating and Air Conditioning, Fifth Edition
By Tom Birch
© 2010 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
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).
Automotive Heating and Air Conditioning, Fifth Edition
By Tom Birch
© 2010 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
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)
Automotive Heating and Air Conditioning, Fifth Edition
By Tom Birch
© 2010 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
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.)
Automotive Heating and Air Conditioning, Fifth Edition
By Tom Birch
© 2010 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
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)
Automotive Heating and Air Conditioning, Fifth Edition
By Tom Birch
© 2010 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
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)
Automotive Heating and Air Conditioning, Fifth Edition
By Tom Birch
© 2010 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
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)
Automotive Heating and Air Conditioning, Fifth Edition
By Tom Birch
© 2010 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
FIGURE 7-30 A condenser is a heat exchanger that transfers heat from the refrigerant to the air flowing through it.
Automotive Heating and Air Conditioning, Fifth Edition
By Tom Birch
© 2010 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
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)
Automotive Heating and Air Conditioning, Fifth Edition
By Tom Birch
© 2010 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
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).
Automotive Heating and Air Conditioning, Fifth Edition
By Tom Birch
© 2010 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
FIGURE 7-33 The volume of gas that enters a condenser is about 1,000 times the volume of liquid leaving it.
Automotive Heating and Air Conditioning, Fifth Edition
By Tom Birch
© 2010 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
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.
Automotive Heating and Air Conditioning, Fifth Edition
By Tom Birch
© 2010 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
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.)
Automotive Heating and Air Conditioning, Fifth Edition
By Tom Birch
© 2010 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
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.
Automotive Heating and Air Conditioning, Fifth Edition
By Tom Birch
© 2010 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
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.)
Automotive Heating and Air Conditioning, Fifth Edition
By Tom Birch
© 2010 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
FIGURE 7-38 The three major hoses/lines are the discharge, liquid, and suction lines. Many systems have two liquid lines.
Automotive Heating and Air Conditioning, Fifth Edition
By Tom Birch
© 2010 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
FIGURE 7-39 Most systems use three of these four refrigerant hose sizes. (Courtesy of Four Seasons)
Automotive Heating and Air Conditioning, Fifth Edition
By Tom Birch
© 2010 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
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.
Automotive Heating and Air Conditioning, Fifth Edition
By Tom Birch
© 2010 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
FIGURE 7-41 Spring-lock and quick-connect couplers are merely pushed together, and a garter spring or plastic cage keeps
them coupled.
Automotive Heating and Air Conditioning, Fifth Edition
By Tom Birch
© 2010 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
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.
Automotive Heating and Air Conditioning, Fifth Edition
By Tom Birch
© 2010 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458