• Guide to Air Conditioning

The Standard in Information and Diagnostic Systems
Guide to
Air Conditioning
The art of keeping cool
on the move
flexibility, adaptability, profitability
 Contents Page
Introduction 4
Refrigerants 4
Refrigerant Legislation 4-5
Operation of an Air Conditioning System 5–8
Component Parts of an Air Conditioning System 9 – 17
Electrical Operating System 17
Equipment Safety – Recharging-Vacuum 18
System Lubrication 19
General safety when working with refrigerants 19
Leak Detection – Air Conditioning System Servicing 20
Fault Tracing and Summary 21
Summary 22
Copyright 2006 Sun Diagnostics UK. All rights reserved. No part of this publication may be reproduced, stored
in a retrieval system, or transmitted, in any form or by any means, electronic or mechanical, by photocopying,
recording or otherwise, without permission of the publisher in writing
2 Guide to Air Conditioning Guide to Air Conditioning 3
 Introduction They are also used in cleaning solvents, sterilant, aerosol propellants and blowing
agents in plastic foam products. In 1987 most developed countries signed the
It is only a few years ago that Air Conditioning was fitted as standard to luxury cars. Montreal Protocol calling for a phased reduction in CFC production to 50% of the
More recently, Air Conditioning is now available as standard on virtually every family 1986 level by the year 2000. It was subsequently reviewed and required a total CFC
car available. In their quest to offer even higher levels of specification and equipment, production phase-out by the 1st January 1996.
it seemed inevitable that manufacturers would offer Air Conditioning. Statistically, at
the time of writing, about 85% of new cars are fitted with Air Conditioning. The European Union agreed a more rapid phase-out. Regulation enforced an 85% cut
in CFC production by the end of 1994. As the production of CFC is reduced and
The main benefits of Air Conditioning are: finally stopped, the cost of CFC will steadily increase. It is estimated the typical
• Driver comfort and hence safety
dealership can recover and re-use approximately 30% of the refrigerant currently used.
• Cools the vehicle interior on hot days. (actually it removes heat!)
The automobile industry has been identified as the single largest venter of CFC R-12
• Removes moisture and therefore speeds up de-misting on cold, damp days.
• Helps to remove dirt and dust from the air in the vehicle interior. Ideal for allergy sufferers. releasing approximately 9% of all CFC’s. This fact clearly emphasises the industry’s
major objective: Design, Manufacture and Acceptance of CFC Recovery and
Recycling Equipment for use in the automotive industry to slow the release of CFC’s
Refrigerants
to the atmosphere. Although the newer R134a refrigerant does not deplete the ozone
In its basic form, a refrigerant is simply a ‘heat carrier’. It carries heat from the interior layer, it has a global warming potential. Therefore in view of this and for reasons of
of the vehicle and disperses it to the atmosphere outside. Although there are many economy, we always recycle the refrigerant wherever possible.
types of refrigerant in use, generally, the main type used in automotive applications is
R-134a. Due to its negative impact on the environment R-12 was phased out at the On the 1st October 2000 a trading ban applied to R12 refrigerant, with a total ‘use ban’ on
end of 1994. R134a refrigerant has been in use since approx 1993. the 1st January 2001. Looking to the future, it is very likely that we will see new refrigerants
in use, such as CO2 (Carbon Dioxide). However, the widespread use of R134a refrigerant
Refrigerant Legislation will ensure that these vehicles will require service for many years to come.
You may have heard of the concern over the ozone layer above the earth. The ozone
layer is a fragile layer surrounding the earth, which acts as a shield against the Sun’s
Operation of an Air Conditioning System
harmful radiation. Scientists have discovered a ‘hole’ in this layer above Antarctica To understand how an air conditioning system works, we first have to know something
and believe it has been caused by the release of chlorofluorocarbons (CFC’s). about heat. Heat is the energy available in an object. All substances contain a certain
The destruction of the ozone layer would result in more radiation striking the earth, amount of heat. Something ‘feels’ hot when it is substantially warmer than our own body
which in turn could result in an increase of skin cancer, damage to the human immune temperature. When something contains much less heat than our own body temperature
system, global warming and drought. CFC’s are chiefly used as refrigerants in we say it is cold. Cold is merely the removal of some heat. When the temperature is in
automotive and building air conditioning units, refrigerators, food display cabinets the zone of about 21 to 26 degrees Celsius all objects are comfortable to touch. As the
and cooling installations. temperature of anything goes above or below this range, we think of it as hot or cold.
4 Guide to Air Conditioning Guide to Air Conditioning 5
 Heat always moves from hot to cold. Whenever there is a temperature difference
Summary
between two objects the heat energy will be transferred from the warmer object to the
cooler one until both objects have stabilised at the same temperature. The greatest The warm air inside the vehicle is blown across the evaporator unit in the vehicle
quantity of heat movement occurs during a change of state. When enough heat is (convection). The heat is absorbed into the cooler refrigerant inside the evaporator
added to a liquid substance it changes into a vapour. Heat is given off during the (conduction). The refrigerant circulates the heat to the condenser unit outside of the vehicle
transformation from vapour to liquid. The quantity of heat used for these changes of (convection). The heat is absorbed into the cooler condenser fins (conduction). Next it is
state is called ‘Latent heat’ and cannot be read on a thermometer. The air conditioning given off to the cooler atmosphere (radiation). Airflow then carries heat away (convection).
system does not add cold to the interior of the vehicle, it removes heat.
Air Movement
Heat Movements Air temperature is only one factor affecting our body comfort. Others include air movements
There are three types of heat movement that we need to discuss to understand the and humidity. Movement of air provides for body comfort due to removal of the following:
working principle of an air conditioning system. Each of these affects how well an (1) nearby moisture, lost by the body during the evaporation process; (2) heat surrounding
automotive air conditioning system works. The three types of heat movements are, the body, lost by the convection process; and (3) heat of surrounding items, generated by
radiation, convection and conduction. the radiation process. That’s why an electric fan, or even a hand fan, provides comfort on a
warm day. Humidity is moisture in the air; Relative humidity is the percentage of moisture in
the air in relation to what the air is capable of holding at a given temperature. Low humidity
Radiation means the air is relatively dry and capable of absorbing moisture. When humidity is relatively
Heat radiates from hot substances, and increases the temperature of surrounding high evaporation processes are slowed. Removal of heat by evaporation decreases. Just as
cooler ones. The Sun is the major source of heat for the Earth. Its energy, transmitted our temperature comfort range is 21 – 26 degrees Celsius, likewise, our humidity comfort
through space, heats the Earth. Direct sunlight is a prime example of heat by ‘Radiation’. range is 45 – 50% relative humidity. Therefore, to be effective on hot, humid days, an air
conditioner must remove both heat and moisture from the vehicle.
Conduction
Heat is absorbed into cooler substances by ‘conduction’. We have all experienced this by Refrigerant
lifting a hot pan from the stove. The handles are hot even though they are not in direct The movement of heat and change of state of a substance leads us now to refrigerants.
contact with the burner. The heat is conducted through the metal of the pan to the cooler This is the chemical substance used as the ‘heat carrier’ within the automotive air
handles. Similarly, a metal bar heated at one end will become hot at the other end. conditioning system. R134a denotes refrigerant; 134a is the type of refrigerant. R134a
is used because it changes state as required by the air conditioning and can do this
Convection within the temperature range of an automotive air conditioning system. R134a is used in
most automotive air conditioners because of its low boiling point (the point at which
The radiator in your house will heat the air by means of convection. The warmer air will
evaporation occurs). At any temperature above approx. -26 degrees Celsius the
move up and is displaced by cooler air. This movement will accelerate the flow of heat.
refrigerant will change state, become vapourised and thereby absorb greater quantities
of heat inside the vehicle. This creates the ‘cooling effect’ of the air conditioning.
6 Guide to Air Conditioning Guide to Air Conditioning 7
 Pressure–Temperature Relationship Refrigerant Circuit - Receiver-Drier Type
The pressure-temperature relationship of the refrigerant is essential. If the pressure of the
refrigerant is low, the temperature will also be low. If the pressure of the refrigerant is high,
the temperature will be high also. Utilising this quality, an increase or decrease in the
refrigerant temperature can be obtained by varying the refrigerant pressure. To operate at
peak efficiency, the refrigerant must be at its coolest state without icing (low pressure) in
the evaporator and its warmest (high pressure) in the condenser. It is mentioned that the
refrigerant vapourises at a low temperature and absorbs great quantities of heat. In the
evaporator, the refrigerant is under very low pressure. Thus, a low temperature is also
obtained. This temperature is much lower than the temperature inside the vehicle. For this
reason, the vehicles heat will travel to the colder refrigerant. As the heat is absorbed , the
refrigerant vapourises and carries the heat from the evaporator to the compressor. The
compressor increases the pressure, and the temperature of the refrigerant vapours. The
vapours are then pumped to the condenser where the heat is transferred to the outside air,
which has a much lower temperature than the vapourised refrigerant, and condensation
takes place. The refrigerant while giving off its heat then returns to a liquid state.
System Operation
An air conditioning system works because of its basic principle:
• Heat travels from warmer to cooler.
• Liquid to vapour.
Evaporator refrigerant absorbs heat in the vehicle passenger compartment
during evaporation.
• Vapour to liquid.
Condenser refrigerant releases heat to the atmosphere during condensation.
Description
All automotive air conditioning systems contain the following 5 basic components:
An air conditioning system is divided into two parts, a High Side and a Low Side.
• Compressor • Condenser
This is true of all air conditioning systems, and the division of these two ‘sides’
• Receiver-drier or accumulator • Expansion valve or orifice tube
• Evaporator always occurs at the same point.
Each of these components is necessary for system operation, and all are dependent
upon the function of one another. Additional components are used for controlling the
system operating temperature, and these vary according to application.
8 Guide to Air Conditioning Guide to Air Conditioning 9
 High Side The compressor acts as a system pump to keep the refrigerant circulating. The suction
side of the compressor draws in the refrigerant vapour. From there, the refrigerant
High side simply refers to the side of the system in which high pressure exists. As passes to the outlet or discharge side of the compressor, where it is compressed
shown in the illustration on page 9 the high side is (following the flow arrows) from the (and thus the temperature is raised). In recent years the scroll type of compressor has
outlet (discharge) side of the compressor, through the condenser, through the receiver become more common place. It offers efficient operation with compact dimensions,
– drier (if equipped) and up to the expansion valve (or the orifice tube). although its function remains the same.
It is the compressor’s job to create the high pressure and high temperature so that It is very likely that we will see electrically driven compressors in the future, especially with
the refrigerant will be able to condense and release heat at the condenser. A pressure the move to 36 Volt electrical systems. The high-pressure, higher temperature, vapourous
differential is created at the expansion valve or orifice tube, the dividing point in the system. refrigerant is then forced out of the compressor and onto the condenser. This high
High side pressures can be typically from 7 to 15 bar, depending on the system used. temperature refrigerant vapour will have a higher temperature than the out-side air
temperature, so it will condense easily. Some models may have a muffler on both the
Low Side discharge and suction sides to help reduce system noise. Therefore, the two main functions
of the compressor are (1) to circulate the refrigerant through the systems, and (2) to raise
Low side is the term used for the side of the air conditioning system in which the low pressure
the pressure and temperature of the refrigerant so it will condense and release its heat.
and temperature exist. From the expansion valve or orifice tube through the evaporator and
accumulator (if equipped) to the inlet of the compressor, the refrigerant is in a low pressure
state. This allows heat to be transferred from inside the vehicle to the ‘colder’ refrigerant, which Condenser
carries it away. Low side pressures are nearly always in the 1 to 2 bar range. The condenser consists of a refrigerant coil
mounted in a series of thin cooling fins. This
Compressor arrangement provides maximum surface
area for heat transfer with a minimum
There are 2 basic types of air conditioning
amount of engine compartment space. The
compressors – the piston type and the rotary
condenser is mounted directly in front of
vane type. Piston-type compressors may have
the radiator where it can receive the full air
their pistons arranged in an in-line, axial, radial,
flow created by the vehicle’s forward motion
or V design. Rotary vane compressors have
and by the engine cooling fan. The condenser
no pistons. The most common compressor
receives heat-laden, high pressure refrigerant
used by car manufacturers is the Piston-type.
vapour from the compressor’s discharge pipe. The
After market systems are usually Vane-type
vapour enters at the top of the condenser and flows
compressors. Automotive air conditioning
through its coils. Heat follows its natural tendency, and
compressors are belt-driven from the engine
radiates from the hot refrigerant to the ‘cooler’ atmosphere. As the vapours are cooled
crankshaft. They have an electromagnetic clutch, which
and flow down through the condenser a point is reached where condensation occurs.
enables the compressor to ‘shut down’ when compressor
operation is not required.
10 Guide to Air Conditioning Guide to Air Conditioning 11
 The vapourous refrigerant becomes a liquid. A large amount of heat is given off by the Second, the receiver-drier also acts as a protection agent for the system. The portion of
refrigerant at the point of condensation. The refrigerant in the lower portion of the the receiver-drier that contains the drying agent absorbs any moisture in the refrigerant.
condenser is a warm high-pressure liquid. In an air conditioning system, which is The drying agent called desiccant is usually in the form of silica gel. It is important that
operating under average heat load, the condenser will have a combination of hot moisture be removed from the system, as it can be extremely harmful to the air
refrigerant vapour in the upper two-thirds of its coils, with the lower third of the coils conditioning system, components and to system operation, causing corrosion and
containing the warm liquid refrigerant, which has condensed. This high pressure, liquid freezing of the system. Where receiver-driers are equipped with a sight glass, this
refrigerant flows from the condenser and towards the evaporator. component allows the service technician to ‘view’ the internal system operation.
Generally, a system using R12 only has a receiver-drier sight glass.
Receiver-Drier / Accumulator
Sometimes the receiver-drier function is taken over by the accumulator. Where there
A receiver-drier is used on air conditioning is nothing mounted in the high side part of the air conditioning system, there has to be
systems which incorporate an expansion an accumulator in the low side part. It is mounted in the low side of the system, after the
valve. It receives refrigerant from the outlet of the evaporator.
condenser. The receiver-drier is
mounted either adjacent to the The function however, is basically the same as that of the receiver-drier, to accumulate
condenser or somewhere or store excess refrigerant and filter and dry the refrigerant. The accumulator also
downstream before the contains a drying agent. If any liquid refrigerant passes out of the evaporator, it will be
expansion valve. It consists stored in the accumulator. Liquid refrigerant is harmful to the compressor. An
of a small tank, a filter, a accumulator is used on air conditioning systems which incorporate an orifice tube. If any
drying agent (desiccant), contamination is suspected due to malfunctioning components or hose leakage
a pick up tube and (on resulting in air ingress, the receiver-drier or accumulator should be replaced.
some applications) a sight
glass. It has several The receiver-drier or accumulator have the same function in the air conditioning system.
functions. First the receiver-
• Acts as a storage tank, receiver-drier for liquid,
drier acts as a storage tank. It and accumulator for liquid-vapour refrigerant.
receives the liquid refrigerant • Acts as a filter.
from the condenser and holds this • Acts as a moisture remover.
liquid until it is required by the • Acts as a vapour-liquid separator.
evaporator. Requirements vary according to
operating conditions. Some manufacturers recommend that the Receiver-Drier or Accumulator is replaced
on a routine basis.
12 Guide to Air Conditioning Guide to Air Conditioning 13
 Refrigerant Circuit – Accumulator Type Metering Action
Refrigerant from the receiver-drier enters the
expansion valve as a liquid under high pressure.
As it passes through the Metering orifice in the
valve, the refrigerant is forced through the small
orifice and ‘sprayed’ out the other side. This
creates a pressure differential, the pressure and
temperature are thus lowered and the atomised
refrigerant can flow through the evaporator and
easily vapourise, thus absorbing heat.
Modulating Action
The thermostatically-controlled valve located within the expansion valve body, fluctuates
towards open or closed position as required to control the liquid refrigerant passing
through the orifice. This ensures that the evaporator receives the proper amount of
refrigerant, depending on the cooling required.
Thermostatic Expansion Valve Orifice Tube
The refrigerant flow to the evaporator must be controlled to obtain maximum cooling, The orifice tube serves the same basic function as the expansion valve, but has a
whilst ensuring complete evaporation of the liquid refrigerant within the evaporator. different configuration. The orifice tube is a straight tube of sintered metal or plastic.
This is accomplished by a thermostatic expansion valve or a fixed orifice tube. Some of these tubes have a filter screen to remove contaminates and a calibrated
orifice tube to meter refrigerant flow. The orifice opening is fixed, the orifice tube does
The thermostatic expansion valve performs three functions:
not affect the compressor operation as does the thermostatic expansion valve which
• Metering action
• Modulating action ‘cycles’ the compressor clutch off and on. The orifice tube has a constant flow through
• Controlling action the fixed orifice, which gives a constant pressure drop.
14 Guide to Air Conditioning Guide to Air Conditioning 15
 Evaporator Air Conditioning Control
The evaporator, like the condenser, consists of Although we have covered the main components and operation of an air conditioning
a refrigerant coil mounted in a series of thin system, there are a number of other control devices to protect system components,
cooling fins. It provides a maximum amount improve cooling and give good driveability. Some of these control devices which may
of heat transfer in a minimum amount of be fitted are:
space. The evaporator is usually mounted in
• Sunlight sensor
a housing under the dash panel or cowl. In
• Ambient temperature sensor
MAX / AC position warm air from the
• Low pressure cut-out switch
passenger compartment is blown across the • High pressure cut-out switch
evaporator coils and fins. The evaporator • High pressure relief valve
receives refrigerant from the thermostatic • Thermal cut-out switch
expansion valve or orifice tube as a low pressure, cold • Evaporator temperature sensor
• Wide open throttle (WOT) switch
atomised liquid. As this cold refrigerant passes through the
• High pressure fan switch
evaporator coils, heat moves from the warm air inside the vehicle into the cooler
refrigerant. When the liquid refrigerant receives enough heat a change of state takes
place. This causes the refrigerant to change from a low pressure liquid, into a low Electrical Operating System
pressure vapour. The thermostatic expansion valve or orifice tube continually meters The air conditioning electrical operating system can be very complicated. Briefly,
the exact amount of refrigerant required to maintain proper heat transfer efficiently. the compressor magnetic clutch is operated by a relay which gets its power from
This action also ensures that all liquid refrigerant will have changed into vapour by the the vehicle battery via fuses. The compressor relay is usually grounded by the vehicle
time it reaches the evaporator outlet. The vapourous refrigerant then continues onto engine management control unit, upon receiving the following:
the inlet (suction) side of the compressor.
• Air conditioning switched on • Blower switched on
The warm air blown across the evaporator will usually contain some moisture • Pressure switch signal • Evaporator temperature signal
(humidity). The moisture in the air will normally condense on the cold evaporator coil
and be drained off as water. A drain tube in the bottom of the evaporator housing With an automatic climate control, the air conditioning system usually has its own
leads the water outside the vehicle. This dehumidification of the air is an added feature Electronic Control Unit (ECU), which controls the compressor, selected temperature
of the air conditioning system that adds to passenger comfort. It can also be used as a and various air outlets. These systems usually have built in diagnostics, or can be
means of controlling fogging of the vehicle windows. An important component in the diagnosed by code readers or scanners.
cooling action of the evaporator is the blower motor/fan, also located in the evaporator
housing. The blower draws warm air from the passenger compartment, over the
evaporator, and blows the ‘cooled’ air into the passenger area.
16 Guide to Air Conditioning Guide to Air Conditioning 17
 Recycling Equipment Operation System Lubrication
The Sun Mobile Recycling Centres use a single pass filtration system. This means that The compressor in an air conditioning system relies on a lubricating oil to lubricate and
the refrigerant is recovered and recycled in a single pass through a master filter with a seal its moving parts. Part of this lubricating oil also mixes and circulates with the
drying medium into a CE approved storage container. Moisture, contaminants and refrigerant to lubricate and seal compressor pistons or vanes. It is very important that
particulates are trapped in the master filter. Clean, recycled refrigerant is stored in the any oil recovered from a vehicle air conditioning system is replaced prior to re-charging
container ready for re-use at any time. Any oil, which may be drawn from the vehicle, is the vehicle air conditioning system. In general R12 systems use a mineral oil and
collected in a separator unit which allows the quantity to be measured. R134a systems use a PAG (Poly-Alkyl-Glykol) oil. Viscosities vary according to
compressor manufacture.
Non-Condensable Gases (i.e. Air)
Some of the Sun Mobile Recycling Centres monitor refrigerant pressure and
Operator Safety
temperature. At pre determined purge pressures, a purge solenoid automatically opens It is extremely important that the necessary safety precautions are followed when
to purge any non-condensables from the machine. handling refrigerants, and working on air conditioning systems. The main danger is
frostbite. Remember that R134a evaporates or ‘boils’ at –26.5 degrees Celsius.
Safety Therefore:
• Always wear the correct protective gloves.
The Sun range of air conditioning equipment is CE approved. Refrigerant storage tanks