Air conditioning cars - some background notes
These notes have been provided by P Manners of Sankyo International
at Reading - they are an interesting read for members who have air
conditioning in mind. (Mar 84)
For many years now car air-conditioning has been offered on
prestige cars such as Rolls Royce, Aston Martin and Ferrari, usually
as an option (and a very expensive one at that) costing around £1,000
or more. However in reason years, a move has been made to make air-conditioning
available more freely to the general public. Specialist installers
like Mark IV, Kool Limited, and Alpinair have emerged to fill this
gap. Let us describe what will happen if you choose to have air-conditioning
fitted to your V8.
First the theory
The air-conditioning system works in a similar way to your refrigerator
you have in your home. It removes heat from inside the cabinet (your
passenger compartment) and pumps it to the outside of the cabinet
(the air outside your car). To accomplish this you require a number
o Compressor which is the pump in the system.
o Condenser which releases heat to the outside air.
o Receiver/drier which stores and dries the refrigerant.
o Hoses to connect the individual components.
o Evaporator assembly which cools and dries the passenger compartment
o Refrigerant R12 which circulates through the system and carries
away the heat extracted from the passenger compartment.
So how does the system work and what happens to the refrigerant?
The R12 is drawn into the compressor and compressed by either a piston
or a vane (depending on the type of compressor), then the high pressure
R12 travels down the discharge hose to the top of the condenser where
it passes its latent heat to the atmosphere via the condenser fins.
As the latent heat is released, the R12 changes in state from a gas
at high pressure to a liquid at high pressure. This liquid congregates
at the lower coil of the condenser and is fed via a liquid pipe to
the drier, where it is dried by a desiccant (drying agent) and stored
momentarily in the reservoir until travelling by a liquid hose to
the evaporator. As it reaches the evaporator it meets a valve called
the expansion valve, which is triggered via a remote sensor on the
other side of the evaporator coil. This valve decides whether to let
R12 through. When it opens and lets R12 through, it goes through a
very small nozzle and expands instantly from a liquid state to a saturated
gas - saturated gas meaning that it is composed of tiny droplets of
During this change in state no work is done so the R12 becomes very
cold. This cold R12 touches the pipes of the evaporator coil and then
makes to coil very cold too. As warm air is passed over this cold
coil it cools appreciably and the water present in the air is condensed
on the cold coil and drains away down a small hole going through the
bulkhead. Obviously the heat in the air is passed to the R12 and so
the R12 changes from a saturated vapour to an unsaturated vapour,
or super heated gas, depending on the temperature of the ambient air.
This low pressure gas goes down the suction hose and into the compressor,
starting the cycle all over again.
Obviously one does not want the air-conditioning functioning all the
time so a system of thermocouples, relays and amplifiers has been
devised to control the output temperature from the evaporator. This
is done by either operating flaps in the heater box to allow hot air
into the cool air, or shutting off the compressor by turning the clutch
Most parts of air-conditioning installations can be done by the enthusiast
with a normal set of tools. However, when setting the system up, it
first needs to be evacuated and then charged with about 65-70psi of
R12. This requires specialist machinery which would only be found
at an air-conditioning installer. Normal mounting parts are required
as well as the components listed earlier in this note.
o New crankshaft pulley with an extra groove.
o Compressor mounting brackets and bolts.
o Various hose clamps and grommets.
o Supplementary fan for the radiator.
o Ducting for the evaporator.
o Drier bracket.
If you do try and install an air-conditioning system, it is most likely
that it will be in your V8. However there is a slight problem - generally
European cars are not designed to take A/C systems - there are no
holes in the block for the mounting brackets, no holes in the bulkhead
for the refrigerant hoses to pass through, and most important, there
is very often no room for either the condenser or evaporator. While
the previous items can be made to fit, it is very often impossible
to make a space in the dashboard or underneath it for a fairly large
item such as an evaporator. With many American and Japanese cars,
the manufacturers have had the foresight to include holes and spaces
for air-conditioning equipment. Therefore A/C installations in those
vehicles are much easier. So if you decide to fit an A/C system to
your V8 do not expect the system to plonk straight in because it will
not! It will need to careful thought and skill in getting it to fit
and look a good installation.