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Information on Car Air Conditioning
The following information on car air conditioning may help
answer any of the questions you may have about car air conditioning.
If having read the following information about car air conditioning, gives you an idea that you are going to need your vehicles air conditioning system looked at, please gives a call today to arrange an appointement for us to check and service your car’s air conditioning.
Because the UK has a temperate climate many people have assumed that air-conditioning in their car would be a rarely used luxury that was not worth paying for.
Now that we have experienced several relatively warm years the benefits of air-conditioning are gradually being generally accepted.
and car air conditioning is now fitted as standard to many cars , its not just a luxury item any more.
Moreover the additional benefits that
are not immediately obvious are now being appreciated by those fortunate to have a good system operating in their car.
What are these benefits?
- The ability to reduce the
in-car temperature to a comfortable level on exceedingly hot days, without having a seventy mile an hour gale buffeting you and being unable to hear the radio or your passengers because of the wind-noise.
- If you have youngish children you will quickly appreciate the extra quiet in the back – aircon seems to almost magically remove the bad temper from most children.
- As aircon also conditions the air, the ability to remove the moisture from the air coming into the car on really muggy days and to achieve a comfortable atmosphere within the car, perhaps in conjunction with the heater control .
the AC button will control the Relative Humidity and the heater if needed will control the temperature leaving you free to enjoy the warmth without being stuffy.
Very few cars are not able to utilise this extremely useful facility.
- The ability to be able to see through the windscreen and all the other glass clearly without a film of mist.
The safety aspect of aircon is often overlooked but is extremely important particularly to the mini people carriers which are becoming so popular now.
Using the AC button to direct the air to the screen the moisture on the glass will be evaporated very rapidly, long before the
heater has had a chance to warm up and will continue this advantage around the side glasses and on to the rear screen. For best effect use the AC button, perhaps in conjunction with the heater in winter and on the fresh air setting (not recirculation).
AC is usually extremely good at de-misting and this safety aspect of good all round visibility, even when
picking up a crowd of wet noisy kids in winter is one of AC’s strong
- The cleaner, fresher air with low Relative Humidity will enhance driver awareness and help prevent drowsiness making your journeys and those of your loved ones safer over long distances as drivers are better able to remain fresh and alert.
- Being caught in a long
traffic jam on a hot day can be purgatory with all the exhaust fumes
coming straight into your open windows, particularly if you are dressed for business – wet under the arms and hot under the collar- probably the time when you most wished that you had bought a car with aircon. This is when AC proves it is one of the nicest affordable luxuries.
- All the air coming into a car with aircon passes through a heat-exchanger, which as it is very cold, quickly becomes dripping with condensation, which collects and drains out under the car.
Air entering this heat exchanger will contain dust and
pollen grains, but by the time the air has passed through this
heat-exchanger (called the evaporator) the vast majority of these
pollutants will have been filtered out, trapped by the condensate and
dripped back onto the road. It is estimated that approximately 80% of all dust and pollen is trapped in this way on each pass through the evaporator – this helps us all but is a source of particular relief to Hay Fever sufferers or Asthmatics.
- By allowing all car windows
to remain closed, even on the hottest days, the aerodynamics of the car remain at optimum, keeping fuel consumption low and exterior noise to a minimum, increasing safety to the driver and passengers.
The engine drives a compressor that sucks the refrigerant gas in the pipe
from the evaporator (that’s the heat-exchanger next to the heater) and
compresses it to quite a high pressure.
This pressure can vary a lot but typically in summer would be around 250 psi.
Gas compressed this much heats up considerably.
This hot, high-pressure gas leaving the compressor is piped to the front of the car where it is connected to a radiator capable of containing these high pressures.
As cool air passes through the radiator it cools the gas sufficiently to turn it into a liquid in exactly the same way that if steam is cooled it turns back into water.
So now the refrigerant is in liquid form coming out of the pipe from the bottom of this radiator (still at high pressure remember) and it is piped back towards the evaporator where there is a restriction in the pipe like a pin hole where it is squirted in a fine spray into the evaporator.
This high-pressure liquid spray now finds itself in an area of very low pressure (remember this is where we came in – it is the area that the compressor is sucking).
It now has the room to expand and turn back into a gas, and it longs to do this, but to turn back into a gas it has to absorb some heat (stretch your mind back to school-days, ‘Latent Heat of Vaporisation and all that’, is it coming back to you?).
It finds the heat necessary to return to a gas by stealing some of the heat from the car’s interior – it takes what it needs and leaves you with just a little heat – perhaps five degrees Celsius. Aha – this is just what you want.
You feelnaturally that the AC is giving off cold, but what is really happening is that it is taking your heat away and leaving you with a lack of heat – which is of course what we call coldness.
There are one or two niceties about the system that we don’t need to go into here but that basically is the whole system, with the gas being compressed, condensed into liquid and returned to a gas in a continuous cycle.
It is the change of state from liquid to gas which achieves the cooling, and if for any reason there is insufficient air passing through the front radiator (the condenser) then the gas will remain as a hot, high-pressure gas and will complete the circuit back to the compressor still as a gas and there will be no cooling.
It is vitally important that the cooling fans are operating
properly, both electro fans and any engine fans, whether directly coupled,
viscous coupled or clutch operated. They may be perfectly adequate to keep the engine cool but the extra task of coping with the AC may sort the sheep from the goats.
Viscous coupled fans in particular have a finite life and eventually
need replacement, as they may no longer be capable of shifting the quantity of air they did in their younger days. An electro fan that may not have had to do any work for six months because the refrigerant has run down and has not been recharged for a time may easily seize up and refuse to work again (particularly common with Ford Scorpios and BMW’s).
When you press the AC button a sensor checks that there is sufficient
refrigerant in the system to not damage the compressor and assuming that there is, it allows 12 volts to flow to an electro-magnetic clutch on the compressor.
At this point you can usually hear a distinct click as the clutch is pulled in
by the electro-magnet and the compressor starts to turn at the same speed as the belt pulley. Within 15 seconds some cooling can be felt but it may take a minute or so to achieve the lowest temperatures.
It is normal for the system to have other sensors to monitor for excessively high pressures (over about 450 psi) and to turn off the compressor to avoid the possibility of damage, and also another to turn on or to increase speed of anelectro fan when pressures rise to about 275 psi – this fan will quickly reduce this pressure.
The temperature of the evaporator is usually maintained at just over freezing point either by a thermostat or by a switch or a valve that controls the pressure and thence the temperature.
This description of a typical AC system is sufficiently accurate for
illustration but some slight differences may be obvious in your own vehicle.
For example many of the earlier systems used the GM Axial 6 cylinder compressor utilising a strange looking 3 legged fuse, this system does not check for sufficient refrigerant pressure as stated in the paragraph above, but will deliberately blow the fuse if the compressor detects that it would be damaged by an insufficient refrigerant charge – Jaguars were the most frequent users in the UK.
Climate Control is a more sophisticated control of temperature to what ever is required by the driver or even the passenger independently.
So that the driver may set a required temperature of say, 18º C and
the passenger may prefer 21º C.
The system will then ensure that both are kept to the temperature they require. However the system tries to anticipate your requirement in other little ways – for example if a sensor detects that the sun is shining, it automatically reduces the settings by two
degrees to compensate for the extra warming of the sunshine through the glass. Several sensors monitor other factors and compensate as necessary.
Climate Control does sound really the bee’s knees and nothing else should be considered. In practice however even the simplest system of AC can work so efficiently that it does make you wonder why anyone should go to the trouble of the complexity of climate control. After a little use it is very easy by adjusting fan speeds and face-level-vent apertures to achieve very acceptable comfort from a very simple system.
My own car at present (VW T5 Van) has a very basic system but is capable of making me very comfortably indeed.
but don’t misunderstand me, AC is brilliant and full climate control just a
little bit more so.
If you have a simple AC system you can cheat though. There is no real
difficulty emulating some of the characteristics of Climate Control with just plain old AC.
If you experience some times when with the AC set on it’s minimum
setting so that it is giving just a little cold and after a short while the air
coming in is too cold for comfort, you could try turning the AC completely off.
In all probability, after a couple of minutes, you will get so warm that you
need to turn the AC on again.
Just pretend you are a Climate Control Module and turn on a tiny amount of heat (with the AC still just turned on – believe me it’s perfectly alright). This combination of a little heat and a little cold should be just what you need – this is all the Climate Control Module is doing
for you if you have this.
The short answer is – yes it does.
But in most cases not much – it all depends on how the car is used. For
example if you get in your car and drive up the motorway for a hundred miles at seventy miles an hour the amount of extra petrol or diesel used to run the AC is negligible. Indeed if you were to turn the AC off and drive instead with a window open to keep cool, you may well find that the increased drag on the car would increase the fuel consumption more than by using the AC button.
On the other hand if your car is mostly used for short journeys there may be a penalty
to pay in petrol for the comfort of continuous AC. For example you get into a stinking hot car and drive 15 minutes to the supermarket. By the time you get there the car is comfortably cool and you leave it in the full sun for an hour while you do the shop. After the hour the car has returned to its stinking hot have to have the AC on full again for the short journey home.
If this is the sort of travelling this car has to do all its life with only short
journeys then the fuel consumption is definitely going to deteriorate but after all you get comfort in exchange. For a few minutes each day the compressor is going flat out, taking power from the engine and in addition both the internal blowers and the electric condenser fans are working hard to cool the car down, causing the alternator to work hard to power them and loading the engine further. If this same car is then used for a long journey, after perhaps ten minutes once the internal temperature is reduced comfortably, the AC throttles itself back – its done the hard work, now it only has to keep the car cool and now the fuel consumption returns to a much more acceptable level. Similarly if on a hot day you drive along and perhaps note that the fuel consumption on your onboard computer shows 34mpg and you turn on the AC and it immediately drops to 28 mpg it would be easy to assume that you were loosing 6 mpg for the AC. Having read the previous few sentences you can now work out that this simplistic assumption is not in fact correct and that within a few minutes the computer will show a gradual rise to near the point at which it started.
I have found little official research on this but in June 2003 the UK Department of Transport sponsored some research into fuel economy on trucks which included the use of AC. This technical evaluation was done by BTAC/IRTE (British Transport Advisory Committee/Institute of Road Transport Engineers) at the MIRA test track at Nuneaton,
at the top speed lorries are able to do with their speed limiters (56mph). At
this relatively low speed the effects of an open window are nothing like so serious as at 70 mph, but even so the effect on fuel consumption was an increase of 7% – quite a considerable increase for this moderate speed. With the windows closed and with the AC on, to quote the official report – “the consolidated data suggest that air conditioning has a minimal affect on fuel consumption”.
Whilst not true there is an element of truth in this story. Up to about
twelve years ago only luxury cars had AC in Britain, some Mercedes, BMW’s, Jaguars, and the top models of the popular makes, such as the Ford Granada/Scorpio and the Vauxhall Senators. Rolls Royce had a nice system and cars that would otherwise be extremely hot and uncomfortable such as Ferrari, Lamborghini and Porsche had to have AC. Not only cars of course, the top-of-the-range Volvo lorry was fitted as standard with AC over twenty years ago and many farm tractors and most combine-harvesters are also so fitted. They used a system much the same as today but the difference was they used a gas popularly known as Freon. This is a trade name but is properly called R12 and it is this refrigerant which is a CFC and the mis-use of it by the AC technicians of the day that is partly responsible for the problems in the ionosphere. This refrigerant was not only used in AC of course, every domestic refrigerator and freezer all over the world was filled with R12 as was every shop fridge or freezer and also the walk-in chillers that butchers have and the huge coldstores that farmers use and the vast freezer warehouses that the processors and the supermarkets use. Food safety legislation over recent decades has forced the use of refrigeration into many areas of life, one has only to notice the large number of chill cabinets in shops for cakes and cheese and drinks and – the list is endless. Additionally there is now a large number of refrigerated lorries on the road where chilledor frozen food must be kept to set temperatures during delivery, take a look when you are next driving on a motorway and first look at the number of Tesco/Asda/Safeway/Sainsbury/etc lorries you see – almost
every one is a reefer (refrig), then look at the number of similar artics used by the supplier companies, I’m sure you will be amazed at the extent of refrigeration in transport. Almost every application
where refrigeration was needed you would find R12 or another similar
refrigerant of the same family of CFC’s, the use of it world-wide was huge.
Every fridge we the general public scrapped would have been broken up by the rag-and-bone man to recover the steel and copper and the R12 allowed to escape.
Hindsight is a wonderful thing and if we were able to put the clock back I’m sure that things would have been done differently, but, up until the mid ’80s the best knowledge available said that the release of R12 into the atmosphere was safe. In those days, if there was a problem in the system, the refrigerant was released as not only was it thought to be safe, it was relatively cheap and therefore the customer would benefit from a completely new charge of
refrigerant with no possible contamination.
One cannot blame the local Sainsburys for what was done on their behalf
by the technicians of the day; they were doing what was thought right at the time. Now most refrigeration is handled by a different family of gasses,
thought to be safer! When a refrigeration or an AC system develops a fault the refrigerant is recovered and recycled – we have moved on. R12 is now only used for the AC in cars built before 1993 but it is not completely dead and buried however – although no longer used in car AC systems it is still widely used by Medicine and also by the Military (among other things it is used to cool the warhead in missiles I believe).
Cars built after about 1993 use a gas that is not a CFC. This is called
R134a and saves using a name that is about as long as a certain Welsh railway station. There should be a sticker in the engine bay telling you if you have R134a.
There are many other refrigerants many of which are based on inflammable gases but obviously these cannot be used in a moving vehicle (imagine a crash, the front radiator could be at 300 psi full of something like butane and has just had a small hole punctured in it – WW2
flame-throwers could learn a thing or two from this). Both R12 and R134a are not flammable. Although R12 is no longer fitted into new cars those built before about 1993 will still need to be recharged with it say every three years.
A fact not always appreciated is that R12 is so efficient that it needs
lower pressures to achieve the same result and thus creates fewer greenhouse gases than R134a.
It varies a lot depending upon a number of factors. Exceptionally I have
serviced AC systems on cars that were still working – just – after ten years
without being recharged. A more usual time for the first recharge would be
around four years. R12 systems will usually last slightly longer than R134a
systems as the R12 molecule is larger and the type of oil used with R12
provides a better seal on the compressor shaft I believe. However although R12 systems lose their charge more slowly than R134a systems this is offset by the fact that is more important for R12 systems not have a low charge as if moisture enters the system (as it can with a low charge) this will mix with R12 to create acids within the system which will do no good at all and will start to corrode the system from the inside. A good rule of thumb would be to recharge a new car after no more than four years and then to recharge at three-year intervals. Most problems occur when the system is struggling because it has insufficient gas to do it’s job properly, and some of the results can be expensive to put right. It’s usually much cheaper to maintain it regularly every three years than to wait for a breakdown and possibly an expensive repair. Particularly do not leave a car with a low charge over the winter months – this is when the air contains most moisture in it and it is likely to enter the system. Get it sorted when you first notice it and you will still have a system next spring – leave it and you take a big risk.
This is usually where I come in and at this point I start asking questions.
Many of the answers I would really like to know as they may require specialist knowledge but there are some questions you could ask yourself and make some judgements upon.
1. Bearing in mind the rule of thumb in the section above, how long since it
was last charged? If you have owned the car for less than about two years and have no other evidence then look further.
2. Is there enough air coming through the face-level-vents? Turn the blower right up, put the air control to face-level and feel how much air is coming out, insufficient could be the result of blocked pollen/dust filters if you have them or a dislodged piece of air trunking under the dash or a vent control that has stuck or even a blower motor not pulling it’s weight. Try pushing the recirculation button (your handbook will show you the logo for this) – if more air comes out of the face-level vents then suspect the pollen filters.
3. The heater may be turned off but is it still working a little and
spoiling the AC? Turn off both heater and AC and with the car running on
tickover for say ten minutes, the bonnet closed and the blower operating, check that the air from the vents is only at ambient temperature and is not
4. Is the AC compressor actually running at all? Look under the bonnet at
where the drive belt is running and get a friend to switch the AC on and off a few times, not too quickly as some systems do not start for several seconds after the switch has been pushed. You should hear a distinct click as the clutch operates and you may then be able to identify which is the compressor, you should then be able to observe that when the AC is turned off the belt turns the pulley only but when it is switched on, the outer plate (which is connected to the compressor internals) turns also. If it does not turn, look first at the fuses – it could be something really simple. Should an AC fuse have blown, before you replace it, check that any electro fan on the radiator is able to turn freely – if it is stiff it may draw excessive current and blow the fuse again. If no fuse has blown probably the most likely scenario is that the gas pressure is so low that the safety switch has operated to prevent the compressor turning and risking damage. Double-check that the blower is actually running – if this fails the AC will not run. Early systems using the large black cylindrical Harrison or Frigidaire A6 compressor (mostly Jaguars and Rolls in the UK) frequently used a strange three-legged fuse mounted on the front end of the compressor, under adverse conditions this blows to protect the compressor and to ensure that the system is looked at and preferably recharged before the fuse is replaced – this is one fuse that almost certainly means that a recharge is necessary, don’t be tempted to just replace the fuse without having the system checked out first.
5. Once you have ascertained that the compressor is running you could try
following the path of the thin pipe coming from the bottom of the condenser (the front radiator). This will often go into a type of metal bottle (the receiver/dryer) that will frequently have a small glass eye in the top of it (the sight-glass). Occasionally this sight-glass is independent and is set into a separate small block. Clean the glass and observe it whilst the compressor is running. Is it virtually completely clear? If you can see a continuous stream of bubbles or even what looks like foam then almost certainly the system needs recharging. It is perfectly normal to see a few bubbles each time the
compressor starts and stops and if you have the later R134a refrigerant a few bubbles may be seen continuously on a very cold day but otherwise the
sight-glass should show only a continuous flow of liquid. The majority of
Vauxhalls and Volvos do not have a sight-glass as most of them use a slightly different system, as do some recent Fords.
They may very well be right but try this first – you may save a lot of
money. Turn the AC off and start the car – does it make a noise now? If it
does, get someone to switch on the AC whilst you listen carefully – does the
noise (A)diminish, (B)stay the same or (C)worsen. If the noise doesn’t start
until the AC is actually switched on then you probably do need a new compressor although it is worth looking to see if the car has a belt tensioner idler pulley as that might just be the source of the noise. It is also worth saying that my twenty year old Mercedes has a noisy compressor – I’ve added a little too much oil and I turn the radio up a little but the AC works fine and it doesn’t leak. If you have (A) above, you could be lucky; the problem is almost certainly a failed compressor pulley bearing – a fairly common fault. As long as you act quickly you could repair this for the price of a new bearing (between £10 and £40), frequently without even having to recover the refrigerant. If you have (B) above you may also be lucky like in (A) but there is a risk that the main support bearing within the compressor has also been damaged – this would require a rebuilt compressor. If you have (C) you probably do need another compressor.
Yes very occasionally. The biggest enemy of AC is moisture within the system
with the refrigerant. The oil used in AC systems is hygroscopic and will absorb
moisture if it gets the chance. Obviously any free moisture floating around in
the system will sooner or later get to the place where the cold is produced and
will promptly freeze into a chunk of ice thus stopping the AC working. As the
evaporator defrosts it will flood the windscreen with moisture and mist up the
screen, after a couple of minutes the chunk of ice will melt and the AC will
resume working again which will quickly demist the screen and then that blessed
bit of moisture will freeze up again and restart the cycle. Every AC system has
a container, which has a bag of desiccant in it to absorb any free moisture.
Depending on the design of the system this container is either a receiver/dryer
or an accumulator. These are intended to be replaced on a regular basis, rather
like an oil filter but perhaps not so frequently.
If the system should develop a fault it is probably worth replacing this
dryer when the fault is cleared but if there is no fault then replacing perhaps
each alternate recharge would be prudent – that is, about every six years. This
is because the desiccant is gradually absorbing moisture that has entered the
system and after a time it reaches the limit of it’s capacity – and it is
important not to approach too close to that limit. If the drier is really quite
old the desiccant can sometime break down and circulate with the
refrigerant and eventually clog the expansion valve. This is quite common on
the older Jaguars with the long
horizontal receiver/drier and manifests itself by the lack of coldness out of
the vents but the expansion valve glowing with hoar frost.
Some of the common driers are only about £20 but a few specialised ones like
some BMW receiver/dryers are more expensive. If you expect about £40 you won’t
be too far out and you may be happily surprised. A few models produced since
about 1998 are incorporating this drier element into the construction of the
condenser which has the advantage that when the condenser is replaced after say
an accident that the drier is replaced as well (as it ought to be), but does
create complications for routine drier replacement in the future – it could be
that the manufacturers have used a much larger quantity of desiccant than
usual, I do not know about this at present.
First let’s get this term ‘top-up’ out of the way. Although this term is
often used, I try to avoid using it as in common with any self respecting
aircon technician, a top-up is never just a top-up. To operate efficiently an
AC system needs a specific quantity of refrigerant. For example a 1990 BMW 525
needs 1,925 grams of R12 whereas a 1999 Rover 200 uses only 560 grams of R134a
plus or minus 25 grams. In other words for optimum operation this Rover needs
somewhere between 535 grams and 595 grams, no more and no less. This is
perfectly typical of modern cars – if the system had only 510 grams or 620
grams it would work slightly less effectively and if the disparity were greater
the efficiency would fall even more, indeed if it had too much refrigerant it
would quickly get to the point of damage to the compressor. Now to get back to
the ‘top-up’, if the quantity of refrigerant is so crucial, how do I know how
much refrigerant to add to the system to bring it to the correct charge? The
short answer is I don’t. Except in only exceptional cases for short term
expedience would I consider just adding refrigerant to an existing system – the
correct procedure which is followed in 99.9% of cases is to recover all
residual refrigerant, evacuate the system to deep vacuum and recharge with the
correct weight of refrigerant.
The evacuation to deep vacuum plays an important part in the recharge; it is
also the lengthiest part of the recharge procedure. The object of this is to
achieve such low pressures within the system that any moisture within the
system will boil away at normal temperatures and be drawn away by the vacuum
pump. In the absence of any other indications (ask yourself the questions on
the page above) a reasonable rule of thumb would be for a first recharge when
the car is four years old and thereafter every three years. It is certainly
cheaper (and more comfortable) to keep a good charge in the system rather than
to repair a system that has been allowed to deteriorate with a depleted
Let’s imagine that your car has been sitting in the supermarket car park in
full sunshine for a couple of hours and is too hot to touch. A reasonable
result can be achieved by following this.
Open all the doors whilst you load up the car
Once in the car, start the engine, run the windows down, set the blowers to maximum,
AC on (ensure the Econ button is OFF), any temperature controls to the lowest
temperature setting, fresh air (not recirc) and air directed through the Face
you have blasted the hot air out of the open windows and filled the car with
colder air, shut the windows and turn the Recirculation control ON (simply
marked as Max on some models).
the settings this way until the fabric of the inside of the car has cooled down
and then either reduce the blower speed or turn the Recirc control to Fresh Air
whichever you choose to do, or perhaps both.
the inside of the car is really cool, turn the blowers down a little further to
suit your comfort and perhaps turn the Face Level Vents upwards to direct the cool air over your head
and come down in the rear of the car.
Alternatively to use the AC to
demist the car the technique is quite different.
If the car is already misted up then simply turn
on the AC, air directed to screen, blowers to highest speed, fresh air selected
and the heat turned to maximum. Many cars simply have a demist button that does
all this for you, but try it out as some are only a heated screen, use of the
AC will be far quicker.
If the weather is warm but the car has misted
up, use full heat on the screen together with the AC until it is safe to back the heater off and
reduce the blower speed. Continue to use the AC in Fresh Air mode (Recirc OFF)
for best demisting.
Return to top
How much would it cost to have Aircon installed
into my car?
This is a question that I am asked constantly, frequently by email. As the
answer is not straightforward and what is more, I do not do installations like
this, I will go into it a little.
If your car does not have AC at all, apart from a little advice, I cannot
help. As to the cost the following paragraphs may help a little. Firstly it
should be noted that to install AC into a car whilst it is being assembled is a
great deal easier and thus cheaper than it is to add it later to a finished
car. Having AC fitted later can be a bit of a shock.
Let me divide cars into two broad categories:
Type 1 Cars built by Japanese manufacturers or by
manufacturers heavily influenced by
Mitsubishi etc, and ROVER when it was building cars influenced by Honda, also
Range Rovers although probably not under Japanese influence.
Type 2 Other cars generally of European origin or
design – Examples: BMW, Ford, Vauxhall etc and DAEWOO (uses GM technology)
Cars in the first category are relatively simple to retrofit AC as the
Japanese tend to install the evaporator under the dashboard in front of the
passengers knees, where it is relatively easy to access.
Type 2 cars generally have the evaporator mounted underneath or behind the
heater matrix right deep behind the dashboard, which means that to access
it the whole dashboard with all the
wiring, airbags, possibly the steering column needs to come out. This can be a
very lengthy and expensive task, possibly up to two days work.
The evaporator is not the whole story of course, many cars have the wiring
loom for AC installed in all models, whether actually fitted with AC or not.
Naturally this simplifies any later retrofit. Also have a look under the
bonnet. Is there room for a mechanic to get his hands into the space around the
engine like a Honda Civic or is the under-bonnet space crammed with components
as are so many cars where a large or powerful engine is shoehorned into a tiny
space, necessitating removal of some other components first in order to mount
the compressor (about the size of a kilo bag of sugar) and the condenser (a
radiator, similar in size and shape to the water radiator and mounted directly
in front of it). General rule: the more room under the bonnet, the easier and
thus cheaper it will be to retrofit.
Type of installation – 4 possibilities
kit – usually the best but most expensive option. For Type 1 cars kit cost £600 to £900 with installation and
charging cost of say £350 to £500 – say a minimum of £950. For Type 2 cars kit
cost £700 to £1200 with installation and charging cost of £500 to £800 – say a
minimum of £1200.
alternative kit – these kits (Diavia is a very good example) are made
specifically for many models and use switches identical to the manufacturers
own, and utilise good quality components. These are installed only by
registered installers who can be found in your local Thomson or Yellow Pages
(or their Web equivalents) under the general heading for Air Conditioning
Equipment. Prices would range from about £1000 up.
installation by an AC technician – varies from excellent to very mediocre. Some
I have seen are every bit as good as a manufacturers installation but some have
been barely adequate. Fortunately some of the mediocre installers eventually go
to the wall. Prices probably from £850.
secondhand system. A possible if the car is not in the first flush of youth and
you may not consider it worth spending around £1000 on it. Let’s imagine a
three year old Mondeo or say a six year old Jaguar. In both of these cases it
may be worthwhile to look in Motor Trader or Exchange & Mart at the section
following the ‘cars for sale’ of your make. This usually contains adverts of
spares for this make and also details of cars written off, a car which has been
rolled will frequently be written off by the insurance company although the
level of damage to the bulk of the car may be minimal. A car like this will
probably still be capable of having the engine running and of ascertaining that
the AC is functioning correctly or at least is still charged with refrigerant.
In these circumstances the AC system may be easily transferable to another car
fairly cheaply. The firm advertising the spares may be able to install them in
your own car or be able to suggest someone who could. I would always recommend
that you discard the secondhand drier and install a new drier from an AC
technician (£20 to £40) who could then charge and test the installed
R12 after October 2000
Now that R12 is now longer available we need to
look at what has to be done when it is time to recharge the system. If your car
has the earlier refrigerant R12 or Freon (basically prior to 1993) and you feel
that it is time to recharge the system let’s stop and consider the options.
The AC is still working reasonably but it is 3 years since it was last recharged and surely it must need a recharge now
The AC is hardly working with little cooling or has stopped completely.
Let’s cover the first one – number 1. Ignore all
my exhortations in the paragraphs above about 3 yearly recharges and hang on to the remainder of the R12 that you have. The alternatives are not as good as R12 so wait until the system is noticeably not cooling as it should and then go on to number 2.
Once you get to number 2. there are several options available probably with your AC
technician’s advice but broadly here is the scenario. If the system has stopped
working because of a perhaps a compressor failure, perhaps the best solution is
that when the compressor is replaced, also replace the drier and retrofit with
the later R134a refrigerant. In many cases a drop in performance may be noticed
but should still be acceptable. A few compressors used on early classic cars
are unable to use R134a, it is also worth looking at the rest of the rubber
hoses as some of the earlier ones are unsuitable for R134a and would need
replacing with more modern hoses.
Even if the compressor is not being replaced it
may be worth considering retrofitting to R134a if the compressor type is
capable of handling the higher pressures required – your AC technician will
know. You may also consider changing a perfectly performing R12 only compressor
for a new compressor which is able to handle R134a, many of which are identical
in size and configuration and can fit directly on to the car.
In all cases of retrofitting to R134a the oil in
the system would need to be changed but the technicalities of the oil type and
the extent and type of the change are beyond the scope of this article.
The other real alternative is to have the
remaining R12 recovered and use one of the ‘drop-in’ replacement refrigerants
for R12 that have been approved for automotive use. Again a replacement drier
may be prudent together with the addition of a small amount of a synthetic
compressor oil. The performance should in most cases approach that of R12, the
loss may not be noticeable. At the moment all the evidence suggests that these
replacement refrigerants would need recharging at slightly more frequent
intervals than R12, as the risk of compressor damage would appear to be greater
as the charge gets low than it was with R12.
The details of the law on R12 after January 2001
appear to have been written by someone with little appreciation of the real
world out there but maybe someone will revise it with a little common sense. Oh
look, there goes another herd of pigs flying past.
I feel that a little update might be appropriate
on this matter nearly two years after the removal of R12. As at September 2002
we have now treated very many cars that were previously R12 systems. The vast
majority of these have been given a refrigerant that is not a mixture of gasses
as are some of the drop-in replacements but is basically the latest refrigerant
R134a together with additives to ensure that the refrigerant carries the
existing lubricant around correctly. In theory at least the system should be
slightly less effective than with R12 but I am happy to report that in practice
I can see no difference with the performance of the alternative refrigerant
If you want to contact me have a look at our
home page – details are there of the area that we cover, my email address and
also there are phone numbers for advice or for making a booking – www.vehicle-electrics.co.uk
On this page too are some links to other websites that I have found
contain some useful information on the AC or other aspects of cars. Some of
these are exceptionally good and are well worth a extended look – the
originators of some of these must have spent an age compiling them and deserve
more than a little credit.
Credit goes to http://www.ac4cars.co.uk for the content of this webpage, If you are looking for airconditioning service in southeast london or
north Kent then please contact them here .
for bookings – 01 474 83 29 41
for advice – 07917 014 551 – (Vodafone)
or by email firstname.lastname@example.org
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