| 140 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 of components: 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 air. 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 R12. |
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. Controls 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 off. Installation 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. General information 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. |