April 05, 2015
Latest from Air-Conditioning Fundamentals , Automotive Air-conditioning and Climate Control Systems :
The early history of transportation systems starts mainly with the horse drawn carriage. This was eventually surpassed by the invention of the automobile. Early automobiles had cabin spaces that were open to the outside environment. This means that the occupants had to adjust there clothing to allow for different weather conditions. Closed cabin spaces were eventually introduced which required heating, cooling and ventilating to meet customer expectations. Early heating systems included heating clay bricks and placing them inside the vehicle or using simple fuel burners to add heat to the vehicle’s interior. Ventilation inside the vehicle was achieved through opening or tilting windows or the windscreen; vents were added to doors and bulkhead to improve air circulation and louvred panels were the equivalent to our modern air ducts. Air flow was difficult to control because it was dependent upon the vehicle speed and sometimes would allow dirty, humid air which contained fumes to enter the interior from the engine compartment. Cooling could be as simple as having a block of ice inside the vehicle and allowing it to melt! Eventually a number of design problems were overcome, these included air vents at the base of the windscreen for natural flow ventilation and electric motors to increase the flow at low speeds. Eventually heat exchangers were introduced which used either the heat from the exhaust system or water from the cooling system as a source, to heat the inside of the vehicle cabin. Early cabin cooling systems were aftermarket sourced and worked on evaporative cooling. They consisted of a box or cylinder fitted to the window of the vehicle. The intake of the unit would allow air to enter from outside and travel through a water soaked wire mesh grille and excelsior cone inside the unit. The water would evaporate due to absorbing the heat in the air and travel through the outlet of the unit which acted as a feed to the inside of the vehicle. The water was held in a reservoir inside the unit and had to be topped up to keep the cone wet otherwise the unit would not operate. The air entering the vehicle would be cool if the relative humidity of the air entering the unit was low.If the relative humidity of the air was high then the water could not evaporate. When the unit was working effectively it would deliver cool saturated water vapour to the inside of the vehicle which raised the humidity levels.These units were only really effective in countries with very low humidity.
In 1939 Packard marketed the first mechanical automotive A/C system which worked on a closed cycle. The system used a compressor, condenser, receiver drier and evaporator (fitted inside the boot/trunk) to operate the system. The only system control was a blower switch. Packard marketing campaign included: ‘Forget the heat this summer in the only air-conditioned car in the world.’ The major problem with the system was that the compressor operated continuously (had no clutch) and had to have the belt removed to disengage the system which was generally during the winter months.Over the period 1940–41 a number of manufacturers made vehicles with A/C systems but these were in small volume and not designed for the masses. It wasn’t until after World War II that Cadillac advertised a new feature for the A/C system that located the A/C controls on the rear parcel shelf, which meant that the driver had to climb into the back seat to switch the system off. This was still better than reaching under the bonnet/hood to remove the drive belt. In 1954–55 Nash-Kelvinator introduced air-conditioning for the mass market. It was an A/C unit that was compact and affordable with controls on the dash and an electric clutch.
Source: AUTOMOTIVE AIR-CONDITIONING AND CLIMATE CONTROL SYSTEMS-Steven daly