Modern Refrigeration and

1
Modern Refrigeration and Air Conditioning
Althouse Turnquist Bracciano
PowerPoint Presentation by Associated Technical
Authors
PublisherThe Goodheart-Willcox Company,
Inc.Tinley Park, Illinois
2
Chapter 4
Compression Systems and Compressors
3
Modules

• Compression Systems
• Compressors

4
Learning Objectives

• Study the five thermal laws relating to
  refrigeration.
• Explain the compression cycle for a domestic
  refrigerator.
• List the components of a refrigeration
  compression system.
• Explain the operation of each component of a
  compression system.
• Trace the flow of refrigerant through a complete
  refrigeration system.

5
Learning Objectives

• Name the two types of motor controls and discuss
  their operation and purpose.
• Describe the five principal types of refrigerant
  controls and their operation.
• Name four different types of compressors.
• Explain how compressors operate.
• Identify the internal parts of a compressor.
• Follow approved safety procedures.

6
Chapter 4
COMPRESSION SYSTEMS MODULE
7
Laws of Refrigeration
4.1

• Fluids absorb heat while changing from a liquid
  to a vapor state.
• Fluids give up heat in changing from a vapor to a
  liquid.
• The temperature at which a change of state occurs
  is constant during the change, providing pressure
  remains constant.
• Heat flows only from a body that is at higher
  temperature to a body that is at a lower
  temperature (hot to cold).

8
Laws of Refrigeration
4.1

• Metallic parts of the evaporating and condensing
  units use metals that have high heat conductivity
  (copper, brass, aluminum).
• Heat energy and other forms of energy
  (electrical, mechanical) are interchangeable.

9
Compression Cycle
4.2

• The compressor changes the refrigerant vapor from
  low pressure to high pressure during the
  compression cycle.
• This transfers heat from the inside of the
  cabinet to the outside.
• Refrigerating system consists of a high-pressure
  side and a low-pressure side.

10
Compression Cycle
4.2
11
Operation ofCompression Cycle
4.2.1

• Note high side and low side.
• The evaporator is on the low side.
• Heat is absorbed in the low side.
• The condenser is in the high side.
• This is where the heat is released from the
  refrigerant.

12
Temperature and Pressure Conditionsin the
Compression Cycle
4.2.2

• Upon starting, compressor moves refrigerant
  molecules from the low-pressure side to the
  high-pressure side.
• It is necessary to speed up the molecules by
  increasing their temperature.
• With each stroke of the compressor, more vapor
  molecules squeeze into the condenser, increasing
  pressure and temperature.
• During compression, pressure increases.
• At the same time, temperature increases.

13
Temperature and Pressure Conditionsin the
Compression Cycle
4.2.2
14
Temperature and Pressure Conditionsin the
Compression Cyclecontinued
4.2.2

• The higher temperature causes a flow of heat to
  the surrounding metal and air.
• Heat moves from the vaporized refrigerant to the
  cooling medium.

15
Temperature and Pressure Conditionsin the
Compression Cycle
4.2.2
16
Temperature and Pressure Conditionsin the
Compression Cycle
4.2.2

• Cooling continues until heat loss causes some
  vapor molecules to become liquid molecules.
• The liquid molecules collect and flow into the
  liquid receiver.
• Temperature and pressure increase until a balance
  is reached.

17
Temperature and Pressure Conditionsin the
Compression Cycle
4.2.2
18
Questions

• When does a fluid give up latent heat?

When it changes from a gas to a liquid.

• Heat always flows from a __________ substance to
  a ______________ substance.

warmer
cooler

• What is the purpose of a compressor?

It changes a low-pressure, low-temperature gas to
a high-pressure, high-temperature gas.

• Into which part of the system is the heat
  absorbed the high side or the low side?

The low side.
19
Questionscontinued

• What main component absorbs heat?

The evaporator.

• During the compression cycle, as the refrigerant
  pressure increases, its ____________ also
  increases.

temperature

• When heat transfers from the high-pressure high-
  temperature refrigerant gas as it flows through
  the condenser, what happens to the refrigerant?
  

It changes to a liquid.
20
Evaporator
4.3

• Two main types of evaporators
• Dry System Evaporators are fed refrigerant as
  quickly as needed to maintain desired
  temperature.
• This system usually has a superheated gas
  leaving the evaporator.
• Flooded System Evaporators are always filled with
  liquid refrigerant.
• The type of refrigerant control used determines
  the type of evaporator used.

21
Evaporatorcontinued
4.3

• Four styles of evaporators for residential
  refrigerators/freezers
• Shell-type.
• Shelf-type.
• Wall-type (used with chest freezers).
• Fin tube-type with forced circulation (used with
  frost-free construction).

22
Evaporator
4.3
23
Evaporator
4.3
24
Evaporator
4.3
25
Evaporator
4.3
26
Accumulator
4.4

• A safety device.
• Prevents liquid refrigerant from flowing back
  into the compressor.
• Liquid refrigerant that flows into the
  accumulator will be evaporated.
• This vapor will flow into the suction line.

27
Accumulator
4.4
28
Suction Line
4.5

• Carries the refrigerant vapor from the evaporator
  to the compressor.
• Must be large enough to avoid resistance of
  refrigerant flow.
• Should slope from the evaporator or accumulator
  down to the compressor to avoid oil pockets.
• May be in contact with all or part of liquid line
  to reduce flash gas in evaporator.

29
Low-Side Filter-Drier
4.5.1

• Included at the compressor end of the suction
  line on some systems.
• May be placed in the system for a short period to
  clean the refrigerant within the system.
• Should offer little resistance to vaporized
  refrigerant flow.

30
Low-Side Filter-Drier
4.5.1
31
Compressor Low-Side orSuction Service Valve
4.5.2

• Allows the technician to connect gauges to the
  system.
• Allows for checking pressures and adding or
  removing refrigerant or oil.
• Sealing caps protect the opening when valve is
  not in use.
• Most new domestic models do not have service
  valves. Saddle valves are used instead.

32
Compressor Low-Side or Suction Service Valve
4.5.2
33
Questions

• What are two main types of evaporators?

A dry system evaporator and flooded system
evaporator.

• Which component determines whether an evaporator
  is considered dry or flooded?

The metering device.

• Name four styles of evaporators for residential
  refrigerator/freezers.

Shell-type, shelf-type, wall-type, and fin
tube-type.
34
Questionscontinued

• What is the purpose of an accumulator?

It prevents liquid refrigerant from flowing back
into the compressor.

• Where is the suction line located on a
  refrigeration system?

Between the evaporator and the compressor.

• Where is the low-side filter-drier placed in a
  system?

In the suction line.
35
Questionscontinued

• What is the purpose of the suction service valve?

To allow a technician to access the system for
charging, removal of refrigerant, evacuation, and
adding refrigerant oil.
36
Compressor
4.6

• A motor-driven device.
• Removes heat-laden vapor refrigerant from the
  evaporator.
• Compresses the vapor into a small volume at a
  high temperature.

37
Compressor High-SideService Valve
4.6.1

• Provides a shutoff between the compressor and the
  condenser.
• Provides an opening for a high-pressure gauge or
  a gauge manifold.

38
Compressor High-SideService Valve
4.6.1
39
Oil Separator
4.7

• Separates the oil from the hot, compressed vapor.
• Placed between the compressor exhaust and the
  condenser.
• Contains a series of baffles or screens that
  collect the oil.
• Oil is returned to the compressor crankcase by
  the use of a float-type valve.
• Commonly used in large commercial installations.

40
Oil Separator
4.7
41
Condenser
4.8

• Removes the condensation heat from the
  refrigerant vapor.
• This heat is picked up in the evaporator and the
  compressor.

42
Condenser
4.8

• Condensers commonly used in domestic
  refrigeration
• Finned-static (natural convection).
• Finned-forced convection.
• Wire-static.
• Plate-static.

43
Condenser
4.8
44
Condenser
4.8
45
Condenser
4.8

• Condensers commonly used in commercial systems
• Finned-static, air-cooled.
• Finned-forced convection, air-cooled.
• Water-cooled, tube-in-a-tube, shell and coil,
  shell and tube, and evaporative type.
• Plate-static.

46
Questions

• What is the purpose of the compressors high-side
  service valve?

It provides shutoff between the compressor and
the condenser and provides access to the high
side for a service technician.

• What is the purpose of an oil separator?

It separates the refrigerant oil from the
high-pressure gas leaving the compressor.
47
Questionscontinued

• Where is an oil separator located?

In the discharge line between the compressor and
the condenser.

• What type of valve is used in an oil separator?

A high-side float.

• What is the purpose of the condenser?

It removes the heat that is picked up in the
evaporator and the compressor.
48
Questionscontinued

• Name two condensers commonly used in domestic
  refrigeration.

Wire-static and finned-force convection.

• Name two types of condensers used in a commercial
  system.

Finned-force convection and water-cooled.
49
Liquid Receiver
4.9

• A storage tank for liquid refrigerant.
• Most have service valves.
• Often found in systems using a low-side float or
  expansion valve-type refrigerant control.
• Not used in capillary-tube systems.
• Seldom used in domestic systems or small
  commercial units.

50
Liquid Receiver
4.9
51
Liquid Line
4.10

• Usually made of copper tubing.
• Domestic units use steel.
• Used to carry liquid refrigerant from the
  condenser to the evaporator.
• Avoid pinching or buckling these lines.

52
Liquid Line Filter-Drier
4.10.1

• Often installed in liquid line.
• Keeps moisture, dirt, and metal from entering
  refrigerant flow control.
• Drying element in filter removes moisture.
• Some equipped with sight glass to indicate
  refrigerant level.
• May contain chemical that changes color to
  indicate moisture in system.

53
Liquid Line Filter-Drier
4.10.1
54
Questions

• What is the purpose of a liquid receiver?

It is a storage tank for refrigerant within the
system.

• Does a capillary tube system require a liquid
  receiver?

No.

• Does a TXV system require a receiver?

Yes.

• Where is the liquid line located on a
  refrigeration system?

Between the condenser (or receiver) and the
metering device.
55
Questionscontinued

• What is the purpose of a liquid line filter drier?

To clean the system of moisture and small
particles.

• What is commonly used with a filter drier that
  determines refrigerant charge in a system?

Sight glass.
56
Refrigerant Flow Control
4.11

• Allows liquid refrigerant to enter the
  evaporator.
• Maintains the required evaporating pressure in
  the evaporator.

57
Refrigerant Flow Control continued
4.11

• There are five types of refrigerant flow
  controls
• Capillary (CAP) Tube.
• Automatic Expansion Valve (AEV).
• Thermostatic Expansion Valve (TEV).
• Low-Side Float (LSF).
• High-Side Float (HSF).

58
Refrigerant Flow Controlcontinued
4.11

• Capillary (CAP) Tube
• Long length of small diameter tubing.
• Reduces pressure by reducing the flow of
  refrigerant through its length.
• Does not use a check valve or a direction control
  valve.
• High and low pressures equalize during the off
  part of the cycle.

59
Capillary (CAP) Tube
4.11.1
60
Refrigerant Flow Controlcontinued
4.11.2

• Automatic Expansion Valve (AEV)
• Used only with the temperature-operated motor
  control.
• Maintains constant pressure in the evaporator
  when the system is running.
• Operates independently of the amount of
  refrigerant in the system.
• Division point between high side and low side.
• Adjustable to the correct evaporator pressure.
• Refrigerant flows only when the compressoris
  running.

61
Automatic Expansion Valve (AEV)
4.11.2
62
Refrigerant Flow Controlcontinued
4.11.3

• Thermostatic Expansion Valve (TEV)
• Sensing bulb mounted at the evaporator outlet.
• Bulb temperature controls the operating of the
  thermostat valve needle.
• Sensing bulb is the opening force spring and
  evaporator pressure are the closing forces.
• Evaporator fills more quickly and permits more
  efficient cooling.
• Used with pressure- or temperature-operated motor
  control.
• Can be used with a multiple evaporator system.

63
Thermostatic Expansion Valve (TEV)
4.11.3
64
Refrigerant Flow Controlcontinued
4.11.4

• Low-Side Float (LSF)
• Used on a flooded system.
• May use either a temperature- or
  pressure-operated motor control.
• Usually has a large liquid receiver.
• Can be used in multiple evaporator systems.

65
Low-Side Float (LSF)
4.11.4
66
Refrigerant Flow Controlcontinued
4.11.5

• High-Side Float (HSF)
• Float is located in the liquid receiver tank or
  in a chamber in the high-pressure side.
• Float controls level of liquid refrigerant on the
  high-pressure side.
• Amount of refrigerant in system must be carefully
  measured.
• Extra refrigerant will overcharge the evaporator
  and cause frosting of the suction line.
• Can be used with a pressure- or temperature-
  operated motor control.

67
High-Side Float (HSF)
4.11.5
68
Questions

• What is the purpose of a refrigerant flow control?

It separates the high side from the low side and
changes a high-pressure liquid to a low-pressure
liquid.

• On a capillary tube system, what happens to the
  high- and low-side pressures during the off cycle?

They equalize.

• What is the purpose of an AEV (automatic
  expansion valve)?

It maintains a constant pressure in the
evaporator.

• Which type of compressor motor control is used
  with an AEV?

A temperature-operated motor control.
69
Questionscontinued

• What are three operating pressures of a TEV
  (thermostatic expansion valve)?

Sensing bulb (opening force), the spring, and
evaporator pressure (closing force).

• Which type of motor control is used with a TEV?

A pressure- or temperature-operated motor control.
70
Questionscontinued

• Which type of system uses a low-side float?

A flooded evaporator system.

• Name two metering devices that are used on
  critically charged refrigeration systems.

The high-side float and the capillary tube system.
71
Motor Control
4.12

• Two types
• Temperature-operated motor control
  (thermostatic).
• Sensing bulb connected to a toggle or snap-action
  switch.
• Adjustment permits differences in operating
  temperatures.
• Pressure-operated motor control (low-side
  pressure).

72
Motor Control
4.12
73
Chapter 4
COMPRESSORS MODULE
74
External-Drive Compressors
4.13

• Bolted together.
• Crankshaft extends through the crankcase and is
  driven by a flywheel (pulley) and belt.
• May be driven directly by an electric motor or
  gas engine.
• Requires a crankshaft seal.
• Seldom used today.

75
External-Drive Compressors
4.13
76
Hermetic Compressors
4.14

• Motor is sealed inside a dome or housing.
• Motor is directly connected to the compressor
  no crankshaft seal needed.
• Usually is spring-mounted inside the hermetic
  dome, reducing vibration.

77
Hermetic Compressors
4.14
78
Types of Compressors
4.15

• Reciprocating.
• Rotary.
• Scroll.
• Screw.
• Centrifugal.

79
Reciprocating Compressor
4.15.1

• Used in majority of domestic, commercial, and
  industrial HVAC systems.
• Basic components include a cylinder and a rod.
• Can be classified by cylinder arrangement, number
  of cylinders, type of crankshaft, or
  construction.
• May be multicylinder, thereby increasing pumping
  capacity.
• Cylinders are usually made of cast iron.
• Usually, crankcase is part of same casting as the
  cylinder.

80
Reciprocating Compressor
4.15.1
81
Reciprocating Compressor
4.15.1
82
Reciprocating Compressorcontinued
4.15.1

• Piston is designed to come as close as possible
  to the cylinder head without touching it. This
  forces as much of the vapor into the
  high-pressure side as possible.
• A valve plate under the cylinder head contains
  both the intake and exhaust valves.
• A connecting rod attaches the piston to the
  crankshaft.

83
Reciprocating Compressor
4.15.1
84
Reciprocating Compressor
4.15.1
85
Reciprocating Compressorcontinued
4.15.1

• Several compressor valve designs are used.
• The intake valve operates at a relatively cool
  temperature and is constantly lubricated by oil
  circulating with the refrigerant vapors.
• The exhaust valves operate at high temperatures
  and must be leakproof.
• Valves open about .010" (.254mm). If movement is
  greater, valve noise develops.

86
Reciprocating Compressor
4.15.1
87
Reciprocating Compressorcontinued
4.15.1

• If a system uses an external motor to drive the
  compressor, a crankshaft seal is necessary. All
  seals use two rubbing surfaces that must be
  lubricated to prevent wear and leakage.
• External drive compressors are driven by a
  V-belt. These are usually driven at less than the
  motor speed. Therefore, the motor belt pulley
  will be smaller than the compressor pulley.
• More than one belt may be used in large-capacity
  installations.

88
Reciprocating Compressor
4.15.1
89
Reciprocating Compressorcontinued
4.15.1

• Some compressors use an eccentric-type crankshaft
  mechanism. This construction reduces vibration
  and the need for connecting rod caps and bolts.
• A scotch yoke mechanism may be used to connect
  the piston to the crankshaft. No connecting rod
  is used. The cylinder and piston are quite long.
• The scotch yoke is popular in small high-speed
  compressors.

90
Reciprocating Compressor
4.15.1
91
Reciprocating Compressor
4.15.1
92
Reciprocating Compressorcontinued
4.15.1

• The reciprocating compressor used on automobile
  air conditioning systems is known as a swash
  plate (or wobble plate) compressor. No
  connecting rod is used.
• The swash plate compressor usually has three or
  more cylinders arranged in a circle around the
  drive shaft.
• The swash plate compressor is double-acting a
  three-cylinder compressor gives a pumping action
  like a six-cylinder conventional compressor.

93
Reciprocating Compressor
4.15.1
94
Reciprocating Compressorcontinued
4.15.1

• Compressor housings support the cylinders,
  crankshaft, valves, oil pump, lubrication lines,
  and the refrigerant inlet and exhaust openings.
• In hermetic compressors, the housing also
  supports and aligns the driving motor.

95
Rotary Compressor
4.15.2

• Two basic types
• Stationary blade.
• Rotating blade.

96
Rotating Blade
4.15.2

• Blades rotate with the shaft.
• Operation
• Low-pressure vapor from the suction line is drawn
  into the opening.
• The vapor fills the space behind the blade as it
  revolves.
• Trapped vapor in the area ahead of the blade is
  compressed until it can be pushed into the
  exhaust line to the condenser.

97
Rotating Blade
4.15.2
98
Rotating Blade continued
4.15.2

• Frequently used as the booster compressor in
  cascade systems.
• Advantages
• Provides a large-size opening into the suction
  line.
• Provides large inlet port openings.
• Has a very small clearance volume.

99
Stationary Blade
4.15.2

• Blade remains stationary and is part of the
  housing assembly.
• Operation
• An eccentric shaft rotates an impeller in a
  cylinder. The impeller constantly rubs against
  the outer wall of the cylinder.
• The blade traps vapor as the impeller revolves.
  The vapor is compressed into a smaller space. The
  pressure and temperature increase.
• The vapor is forced through the exhaust port,
  entering the condenser.

100
Stationary Blade
4.15.2
101
Stationary Blade
4.15.2
102
Rotary Cylinder Construction
4.15.2

• Made of cast iron.
• Has intake and exhaust ports.
• Usually mounted on an end plate.
• Exhaust valve reed is mounted on the exhaust port
  outlet of the compressor.

103
Rotary Compressor Construction
4.15.2

• Rotating blade compressor rotor is a fixed part
  of shaft.
• Stationary blade compressor rotor accurately
  fits the eccentric. The eccentric is a fixed part
  of the shaft.

104
Scroll Compressor
4.15.3

• Very few moving parts.
• Smooth compression cycle with low torque.
• Low noise and low vibration levels.

105
Scroll Compressor Operation
4.15.3

• Generates a series of crescent-shaped gas pockets
  between two scrolls.
• One scroll remains stationary.
• The other scroll the orbiting scroll rotates
  through the use of the swing link.
• Pockets of gas are slowly pushed to the center,
  reducing their volume.
• When the pocket reaches the center of the scroll,
  the gas is at high pressure.
• Discharge is through the center port.

106
Scroll Compressor Operation
4.15.3
107
Scroll Compressor Operation
4.15.3
108
Screw Compressor
4.15.4

• Two basic types
• Open, externally driven compressor, used most
  often with ammonia systems.
• Hermetic, internally driven compressor, using
  halocarbon refrigerants.

109
Screw Compressor Operation
4.15.4

• A pair of helical rotors trap and compress air as
  they revolve in an accurately machined cylinder.
• The male rotor is driven by the motor and has
  four lobes.
• The female rotor has six lobes. It meshes with
  and is driven by the male rotor.
• The refrigerant vapor is drawn in by the meshing
  rotors.

110
Screw Compressor Operation
4.15.4
AMale rotor. BFemale rotor
111
Screw Compressor Operation
4.15.3
112
Screw Compressor Operation continued
4.15.4

• The rotors provide a continuous pumping action,
  trapping and compressing the refrigerant.
• A capacity control device provides for variable
  unloading and accurate temperature control of a
  conditioned space.

113
Centrifugal Compressor
4.15.5

• Used in large-capacity systems from 50 to 5,000
  tons.
• Simple design no valves, pistons, or cylinders.
• Pumping efficiency increases with speed.

114
Centrifugal Compressor Operation
4.15.5

• Vapor is fed into housing near the center of the
  compressor.
• Rapidly rotating impellers move the vapor
  outward, forcing it against the outer diameter
  and increasing its pressure.
• Several impellers are put in series to multiply
  the pressure increase and further compress the
  vapor.

115
Centrifugal Compressor Operation
4.15.5
116
Compressor Motors
4.16

• External drive compressor.
• Motor connected to compressor by one or more
  V-belts or by direct drive.
• Hermetic compressor.
• Motor is mounted under the same dome as
  compressor.

117
Mufflers
4.18

• Used on most hermetic units and many
  external-drive systems to reduce noise.
• May be located at both the intake and the exhaust
  openings of the compressor.
• Constructed of brazed cylinders with baffle
  plates mounted inside.

118
Mufflers
4.18
Note discharge and suction (intake) mufflers.
119
Lubrication
4.20

• Specific lubricating oils are available for
  reciprocating and rotary compressors.
• A small pump is used for force-feed or pressure
  systems. It is usually mounted on one end of the
  crankshaft.

120
Lubrication
4.20
121
Compressor Volumetric Efficiency
4.21

• For efficient operation, the volumetric
  efficiency must be as high as possible.
• Items such as head pressure, clearance space, and
  size and condition of the valve openings impact
  volumetric efficiency.
• Formula
• Volumetric efficiency

__Actual volume__
(
)
X 100
Calculated volume
122
Compression Ratio
4.22

• The relationship of the high-side absolute
  pressure to the low-side absolute pressure.
• Ratios vary up to 101.

123
Check Valves
4.23

• Prevent refrigerant vapor, oil, or liquid
  refrigerant from backing up into the evaporator
  or other devices.

124
Check Valves
4.23
125
Unloader
4.24

• Makes it easier to start the compressor by
  temporarily reducing high-side pressure at the
  cylinder head.
• May be operated mechanically, electrically,
  hydraulically, or by a solenoid valve.

126
Unloader
4.24
127
Gaskets
4.25

• May be made of special paper, synthetic material,
  plastic, or lead.
• Used between bolted parts such as cylinder heads,
  valve plates, and crankcase openings.

128
O-ring
4.26

• Sealing device.
• Material used for O-ring depends on temperature,
  pressure, fluids to be controlled, and useful
  life required.

129
O-ring
4.26
130
Crankcase Heater
4.27

• Evaporates liquid refrigerant trapped in the oil.
• Required on remote installations where ambient
  temperature is lower than evaporator temperature.
• Reduces risk of oil slugging.

131
Crankcase Heater
4.27
132
Questions

• Name two types of compressor motor controls.

Temperature-operated and pressure-operated.

• Name two types of compressor drives.

Direct drive and belt drive.

• Name five types of compressors.

Reciprocating, rotary, scroll, screw, and
centrifugal.

• On a reciprocating compressor, where are the
  discharge and suction valves located?

In a valve plate under the compressor head.
133
Safety
4.28

• Always be alert to hazardous situations or
  procedures and equipment that may be dangerous.
• Always follow recommended procedures.
• Always wear goggles when working on a
  refrigerating system.
• Handle all parts with care. Clean and dry each
  part that is dismantled.
• Do not allow moisture to enter the refrigerating
  mechanism.

134
Safetycontinued
4.28

• Make sure settings and adjustments are done
  correctly. Improper temperatures cause food to
  spoil.
• Take care when tightening tube connections,
  installing gaskets, replacing electrical
  terminals, and soldering fittings.

135
Glossary

• accumulator
• Storage tank that receives liquid refrigerant
  from the evaporator and prevents it from flowing
  into the compressor before vaporizing.
• centrifugal compressor
• Pump that compresses gaseous refrigerants by
  centrifugal force.
• check valves
• Allow fluid to flow in only one direction in a
  system.
• clearance space
• The space left in the cylinder when the roller or
  piston ends its compression stroke.

136
Glossary

• compression ratio
• Ratio of the total volume of the cylinder to the
  clearance space.
• compressor
• Pump of a refrigerating mechanism that draws a
  low pressure on the cooling side of the
  refrigerant cycle and squeezes or compresses the
  gas into the high-pressure or condensing side of
  the cycle.
• compressor volumetric efficiency
• The relationship between the actual performance
  of a compressor and theoretical performance of
  the pump based on its displacement.

137
Glossary

• condenser
• The part of the refrigeration mechanism which
  receives hot, high-pressure refrigerant gas from
  compressor and cools gaseous refrigerant until it
  returns to its liquid state.
• evaporator
• Part of a refrigerating mechanism in which the
  refrigerant vaporizes and absorbs heat.

138
Glossary

• head pressure
• The pressure the compressor must pump against.
• liquid receiver
• Cylinder (container) connected to condenser
  outlet for storage of liquid refrigerant in a
  system.
• oil separator
• Device used to remove oil from gaseous
  refrigerant.
• rotary compressor
• Mechanism that pumps fluid by using rotating
  motion.

139
Glossary

• screw compressor
• Compressor constructed of two mated revolving
  screws.
• scroll compressor
• A compressor that uses the interaction of two
  spiral coils (scrolls) to compress a vapor.
• suction line
• Tube or pipe used to carry refrigerant gas from
  evaporator to compressor.
• unloader
• Temporarily reduces the high-side pressure at the
  cylinder head during compressor startup.