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 5
Refrigerant Controls
3
Learning Objectives
? Explain the purpose and operation of
refrigerant control devices. ? Name the six main
types of controls and explain their operation.
? Define terms related to refrigerant control
operations. ? Compare the various charging
elements used on refrigerant controls. ? Explain
the fast evaporation of liquid into a vapor.
4
Learning Objectives

• Determine the proper size capillary tube to be
  used for specific applications.
• Explain the operation of special refrigerant
  controls.
• Define the purpose and function of three types of
  solenoid valves.
• Follow approved safety procedures.

5
Refrigerant Control
5.1

• Used in a refrigeration system to change the
  pressure of the refrigerant.
• Is placed between the liquid line and the
  evaporator.
• Reduces the high pressure in the liquid line to
  low pressure in the evaporator.

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Six Types of Refrigerant Controls

• Automatic Expansion Valve (AEV).
• Thermostatic Expansion Valve (TEV).
• Low-Pressure Side Float (LSF).
• High-Pressure Side Float (HSF).
• Capillary Tube (Cap Tube).
• Thermal-Electric Expansion Valve.

7
Automatic Expansion Valve
5.1.1

• Operated by low-side pressure as the closing
  force and spring pressure as the opening force.
• Throttles liquid refrigerant in the liquid line
  down to a constant pressure. While compressor is
  running, liquid refrigerant is sprayed into the
  evaporator.
• Sometimes called a dry system, since evaporator
  is never filled with liquid refrigerant, but with
  a mist.
• Valve capacity should equal the evaporator
  capacity.

8
Automatic Expansion Valve
5.1.1
9
Bellows AutomaticExpansion Valve
5.3

• Valve seat is softer than needle.
• Spring is attached at both ends.
• May be adjusted for either pressure or tension.
• Attached to the evaporator by threaded fittings
  or a two-bolt flange.
• Used mainly on domestic air conditioning units or
  vending machines.

10
Bellows AutomaticExpansion Valve
5.1.1
11
Diaphragm AutomaticExpansion Valve
5.1

• Has stops to prevent excessive movement of the
  diaphragm.
• Diaphragm separates the atmospheric pressure and
  the system pressure.
• Three forces control valve
• Adjustable spring.
• Spring beneath diaphragm.
• Outlet pressure underneath the diaphragm.

12
Diaphragm AutomaticExpansion Valve
5.1
13
Thermostatic Expansion Valve (TEV)
5.1.2

• Sensing bulb includes liquid-charged,
  gas-charged, liquid cross-charged, and gas
  cross-charged.
• Note Liquid-charged and gas-charged use the same
  refrigerant in the system and bulb. Cross-charged
  uses a fluid in the sensing bulb different from
  the system refrigerant.

14
TEV
5.1.2

• Flow is through the valve into the evaporator.
• Low-side pressure, the temperature of the
  evaporator outlet, and spring pressure control
  flow.
• Provides a high flow rate as the evaporator
  empties (warms).
• Reduces flow as the evaporator fills (cools) with
  refrigerant.

15
Operation of TEV
5.1.2

• With unit running, temperature in sensing bulb is
  10F (5.6C) warmer than the refrigerant
  temperature in the evaporator.
• This temperature difference produces different
  pressures and different forces. This is described
  as the superheat of the bulb over the refrigerant
  temperature inside the evaporator.
• The pressure in the sensing bulb is greater than
  the pressure in the evaporator.
• As temperature increases or decreases, the
  pressure will also increase or decrease.

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Operation of TEV
5.1.2
17
Operation of TEV continued
5.1.2

• When compressor stops, low-side pressure and the
  sensing bulb pressure tend to equalize.
• The needle is forced into its seat. Refrigerant
  flow stops.

18
TEV Design
5.1.2

• The liquid and evaporator lines are connected to
  the brass valve body.
• Needle and seat are inside the body.
• Needle is joined to a flexible metal bellows or
  diaphragm.
• Bellows is moved by a rod connected at the other
  end to a sealed bellows or diaphragm and sensing
  element.

19
TEV Design
5.1.2
20
TEV Design continued
5.1.2

• The diaphragm is joined to the sensing bulb by
  means of a capillary tube.
• Fluid that charges the sensing element is labeled
  by color, letter, or number by manufacturer.
• A strainer located between the liquid line
  connection and orifice keep dirt from the needle
  and seat.

21
Questions

• Where is a refrigerant control located in the
  refrigeration system?

Between the liquid line and the evaporator.

• What is the purpose of a refrigerant control in a
  refrigeration system?

It changes the high-pressure, high-temperature
liquid to a low-pressure, low-temperature liquid.

• Which pressures operate the automatic expansion
  valve?

The spring pressure is the opening force and the
low-side pressure is the closing force.
22
Questions continued

• Which type of motor control can be used with the
  automatic expansion valve system?

A temperature control.

• Which types of thermostatic expansion valves use
  the same refrigerant in the system as in its
  sensing bulb?

The liquid-charged bulb and gas-charged bulb.

• What are three operating pressures of a TEV?

Low-side pressure, sensing bulb pressure, and
spring pressure.
23
Questions continued

• What happens to the quantity of refrigerant in
  the evaporator of a TEV system as the temperature
  of the sensing bulb increases?

The quantity of refrigerant increases.

• Do the pressures of a TEV system equalize during
  the off cycle?

No.

• What is commonly located before the inlet of a
  TEV?

A strainer.
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Flash Gas
5.1.2

• Refrigerant that evaporates instantly (flashes)
  and turns into a vapor while passing through the
  refrigerant control orifice.
• The instant vaporizing of some of the liquid
  refrigerant cools the remaining liquid to the
  evaporating temperature.
• Amount of flash gas depends upon the temperature
  of the refrigerant in the liquid line and the
  pressure inside the evaporator.
• Flash gas reduces the valve capacity.
• The amount of flash gas can be reduced by
  clamping the liquid line to the suction line.

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Superheat
5.1.2

• The difference in temperature between the vapor
  in the low side and in the sensing bulb.
• Increasing superheat starves the evaporator only
  part of the evaporator is filled with liquid
  refrigerant.

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Superheat
5.1.2
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Liquid-chargedSensing Element
5.1.2

• Sensing element is charged with the same
  refrigerant as the system.
• Maintains a constant superheat, or compressor
  superheat setting, even though low-side pressures
  and temperatures change.
• Sensing element controls thermostatic valve
  operation.

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Liquid-chargedSensing Element
5.1.2
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Liquid Cross-chargedSensing Element
5.1.2

• Uses a liquid different from the refrigerant in
  the system.
• Some liquid is always present in the element,
  regardless of temperature.
• Valve closes quickly when the compressor stops.
• Load on compressor is reduced at startup.
• As suction pressure is reduced, superheat is
  reduced.
• Valve is more responsive to changes in suction
  pressure than to changes in sensing bulb
  temperature.

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Liquid Cross-chargedSensing Element
5.1.2
31
Gas Cross-chargedSensing Element
5.1.2

• Uses the same refrigerant as the system.
• Charge provides that all liquid is vaporized at a
  predetermined temperature.
• Designed for temperature range from 30F to 60F
  (1.1C to 15.6C).

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Gas Cross-chargedSensing Element
5.1.2
33
Gas Cross-chargedSensing Element (Adsorption)
5.1.2

• Sensing bulb is charged with a liquid different
  from the system refrigerant.
• At the desired temperature, all the liquid has
  vaporized.
• Some elements contain two substances one is a
  non-condensing gas, such as carbon dioxide, that
  provides the pressure in the element. The other
  is a solid, such as carbon, silica gel, or
  charcoal. These substances can adsorb gas.

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Gas Cross-charged Sensing Element (Adsorption)
continued
5.1.2

• Adsorption, the ability of a substance to adsorb
  gas depends upon temperature.
• Gas is more readily adsorbed at low
  temperatures.
• Sensing elements rely on adsorption to control
  the refrigerant needle valve opening in the
  thermostatic expansion valve.
• Pressure-temperature lag in operation allows for
  use on any refrigeration or air conditioning
  system.

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Thermal-Electric (Solid State) Expansion Valve
5.1.2

• Depends on the use of thermistors, which are
  directly exposed to the refrigerant in the
  suction line, to control the expansion valve
  needle opening.
• Refrigerant flow is controlled by the temperature
  in the suction line.
• Bleed valves have a small slot in the valve seat,
  allowing pressure to balance during the off
  cycle.
• Allows for use of low-starting-torque compressor
  motors.

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Thermal-Electric (Solid State) Expansion Valve
5.1.2
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Expansion Valvewith Pressure Limiters
5.1.2

• Prevents overloading the condensing unit.
• Designed for systems in which the evaporator
  pressure must not exceed a safe operating limit.
• Consists of a diaphragm and a spring placed
  between the sensing element and the needle valve.
• Diaphragm will collapse if low-side pressure
  exceeds a certain set value.
• May be mechanical (conventional) or
  pressure-limiting (MOP maximum operating
  pressure).

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Expansion Valvewith Pressure Limiters
5.1.2
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Sensing Bulb Mounting
5.1.2

• Location is important mount on top of the
  suction line.
• On a vertical suction line, capillary tube of the
  bulb should always enter from the top of the
  bulb.
• Clean suction line and bulb with steel wool prior
  to assembling.
• Must be wrapped in insulation to make sure only
  suction line temperature is read.

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Sensing Bulb Mounting
5.1.2
41
Thermostatic Expansion Valve
5.1.2

• Capacities vary according to
• Orifice size. Undersizing can lead to starving of
  the evaporator oversizing can cause
  hunting/surging of the valve.
• Pressure difference between the high side and the
  low side (increasing pressure difference will
  increase the rate of refrigerant flow).
• The temperature and condition of the refrigerant
  in the liquid line.

42
Questions

• What results from the instantaneous evaporation
  of a liquid?

Flash gas.

• When flash gas is present in a liquid line, what
  happens to the capacity of an expansion valve?

It decreases.

• Which component can be used to reduce flash gas?

A heat exchanger.
43
Questions continued

• When measuring superheat, what two temperatures
  must be known?

Evaporator saturation temperature and sensing
bulb temperature.

• Which will cause a starved evaporator an
  increase or a decrease in superheat?

An increase in superheat.

• Which two TEV sensing bulbs do not use the same
  refrigerant that is in the system?

A liquid cross-charged bulb and a gas
cross-charged bulb.
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Solenoid Valve Principles
5.1.3

• Consists of a movable armature made of an iron
  alloy and attached to the valve needle, all
  sealed into a valve body.
• Coil is wound around the valve housing that
  contains the armature.
• May be activated by a thermostat.
• Used to control the temperature of a refrigerator
  or room.

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Solenoid Valve Principles
5.1.3
46
Types of Solenoid Valves
5.1.3

• Two-way valve controls flow of refrigerant
  through a single line.

47
Types of Solenoid Valves continued
5.1.3

• Three-way valve with an inlet that is common to
  two opposite openings.
• Controls refrigerant flow in two different
  lines. (Used mainly on commercial refriger-
  ating units).

48
Types of Solenoid Valves continued
5.1.3

• Four-way reversing valve used on heat pumps.

49
Types of Solenoid Valves continued
5.1.3

• Pilot-operated solenoid valve used for large
  commercial applications.

50
Equalizer
5.1.3

• Compensates for any pressure drop through the
  evaporator while the compressor is running.
• Used if the pressure drop between the inlet of
  the evaporator and the outlet is more than 4 psi
  (28kPa).
• Provides the same pressure as that in the suction
  line at the sensing bulb location.
• Equalization of pressure permits accurate
  superheating adjustments.

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Equalizer
5.1.3
52
Hunting
5.1.3

• Sometimes referred to as surging, hunting occurs
  when a valve first opens too wide, then closes
  down too much.
• When a valve is hunting excessively, refrigerant
  flow provided to the evaporator is not uniform.
• The less hunting, the more effective the system
  will be.
• Liquid may reach the compressor and cause damage.
• Hunting can be caused by a valve that is too
  large for the system.

53
Low-Side Float
5.1.4

• A simple and efficient refrigerant control
  method.
• Used with large industrial systems and in some
  water cooling systems.
• Requires a means of returning excess oil to
  compressor. Extending the suction tube to the
  bottom of the float pan ensures oil return.
• May use a pressure-operated motor control or a
  thermostatic motor control.

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Low-Side Float
5.1.4
55
High-Side Float
5.1.5

• Located in the high-pressure side of the system.
• Evaporator must be equipped with a special oil
  return.
• May use either a thermostatic or a
  pressure-operated motor control.

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High-Side Float
5.1.5
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Capillary Tube
5.1.6

• Acts as a constant throttle on the system.
• Equipped with a filter or a filter-drier to
  remove moisture or dirt from refrigerant.
• Amount of refrigerant must be carefully
  calculated.
• Must be used with a thermostatic motor control.
• Fittings must be leak-proof.

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Capillary Tube
5.1.6
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Comparing Refrigerant Controls
5.2
Note Pressure-time cycle varies with refrigerant
used.
60
Check Valves
5.3

• Limit the directional flow of refrigerant.
• Rotary and gear compressors have check valves in
  the suction line, preventing high-pressure vapor
  and refrigerant oil from backing up into the
  evaporator.
• May use either a disk or solid ball in
  construction.
• In multiple systems that operate at different
  temperatures, check valves keep refrigerant
  vapors in warmer evaporators from backing up into
  the colder evaporators.

61
Check Valves
5.3
62
Suction Pressure Valves
5.4

• Evaporator Pressure Regulator (EPR)
• Required on multiple systems in which
  evaporators operate at different temperatures.
• Required on most automobile air conditioning
  systems due to compressor operating at various
  speeds.
• Crankcase Pressure Regulator (CPR)
• Used to keep compressor suction pressure at a
  safe level.
• Prevents overloading the compressor.

63
Questions

• Which type of solenoid valve controls refrigerant
  flow through a single line?

Two-way valve.

• Where is a four-way reversing valve commonly used?

In a heat pump system.

• Where is a low-side float metering device
  commonly used?

In large industrial systems.

• Which type of motor control can be used on a
  low-side float system?

Thermostatic or pressure-operated control.
64
Questions continued

• Which type of motor control can be used on a
  capillary tube system?

A temperature control.

• What is the purpose of a check valve?

To allow refrigerant to flow in one direction.

• Where is a check valve located on a
  multiple-evaporator system?

At the outlet of the coldest evaporator.
65
Questions continued

• What is the purpose of an EPR valve (evaporator
  pressure regulator)?

It is used to maintain constant evaporator
pressure.

• Where is an EPR valve located on a multiple
  evaporator system?

At the outlet of the warmer evaporators.

• What is the purpose of a CPR (crankcase pressure
  regulator)?

It prevents the compressor from overloading.
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Safety
5.5

• Attach a 24-hour pressure-time recorder to any
  new installation. It will ensure the system is
  operating within safe pressure limits.
• Keep floors clear of debris.
• Wear safety goggles when working on refrigeration
  systems.
• When lifting, use leg muscles do not use your
  back.

67
Safety continued
5.5

• Always have good ventilation and good lighting
  when working on systems.
• All electrical circuits must be well-insulated to
  avoid shock.
• All metal parts of refrigerating mechanisms
  should be grounded.
• When removing a valve from a system, use two
  wrenches.

68
Glossary

• adsorption
• The adhesion of a thin layer of molecules of a
  gas or liquid to a solid object. There is no
  chemical combination between the gas and the
  solid substance (adsorber).
• automatic expansion valve
• Pressure-controlled valve that reduces
  high-pressure liquid refrigerant to low-pressure
  liquid refrigerant.
• check valve
• Device that permits fluid flow in only one
  direction.
• equalizer
• A device used to balance pressure in a system or
  balance liquid levels between two containers.

69
Glossary

• flash gas
• Instantaneous evaporation of some liquid
  refrigerant in evaporator, cooling the remaining
  liquid refrigerant to the desired evaporation
  temperature.
• hunting
• The process of cycling above and below the set
  point.
• pressure limiter
• Device that remains closed until a certain
  pressure is reached, then opens and releases
  fluid to another part of system or breaks an
  electric circuit.
• refrigerant control
• Device that meters flow of refrigerant between
  two areas of a refrigerating system. Maintains
  the pressure difference between high-pressure and
  low-pressure side of the system while unit is
  running.

70
Glossary

• solenoid valve
• Electromagnet with a moving core. It serves as a
  valve or operates a valve.
• superheat
• The temperature of vapor above its boiling
  temperature as a liquid at that pressure or the
  difference between the temperature at the
  evaporator outlet and the lower temperature of
  the refrigerant evaporating in the evaporator.
• thermistor
• A semiconductor with electrical resistance that
  varies with temperature.