How it Works: Air-Conditioning

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How it Works: Air-Conditioning

A.R.A. Chairman Air-Conditioner, as installed in a 1963 US Ford Fairlane
A.R.A. Chairman Air-Conditioner, as installed in a 1963 US Ford Fairlane.

Frigiking unit as fitted to 1962 Ford Thunderbird
Frigiking unit as fitted to 1962 Ford Thunderbird.

Frigiquip Strato Dawn in early model US Ford
Frigiquip Strato Dawn in early model US Ford.

Boot installation of Air-Conditioner
Rarely seen in Australia is the boot installation - which was a popular alternative in the USA.

Boot installation of Air-Conditioner
Early under-dash Mark IV Monitor.

Eaton under-dash air conditioner
The more compact, but more obvious Eaton under-dash air conditioner.

Vanguard Trimline under-dash air-conditioner
Vanguard Trimline under-dash air-conditioner.

Gaining Popularity since 1948

These days we take air conditioning for granted - unless of course it breaks down. But not that many decades ago, the vast majority of motorists had to travel through sluggish traffic sitting on sticky vinyl bench seats as they tried to get home. Take a Sunday drive through summer and the open window was the only real solution to flow-through ventilation - and that introduced wind, dust, and pollen from the open countryside. Right up until the early 1980s air conditioning was usually an option that many could not afford - and the 1970s in particular was a decade when the aftermarket installation was at its height.

The very first crude attempts at car air-conditioning came in the USA in 1948, with the industry gaining strength until 1953, when about one in every 150 cars was refrigerated. From those days on cooling the driver became one of the newest multi-million-dollar industries in America. The story was not the same here in Australia, thanks mainly to the prevalence of English cars which, because of the climate from which they originated, and perhaps because the engines were underpowered anyway, air-conditioning was not a primary concern.

Australia, like much of America, was a pretty hot place in summer - and the aftermarket air-conditioner grew in popularity during the early 1970s. But this was a time when you did not simply tick the options box - rather you would take your car to a air-conditioning specialist to see what could be done. There were many available units - and each owner had to consider costs, models, expense of operation, its effect on their car - then evaluate against general driving discomfort without the air-conditioner.

First, owners had to understand how the unit worked and what constituted a genuine refrigerating unit. The auto air conditioner worked the same way a room unit did. Back then a room unit had all its major parts within one housing, while the car unit (because of space requirements) has them separated - an idea that would later catch on with domestic air-conditioners with the split-system. The evaporator (where the cold air came from) and the controls were inside the passenger compartment (except on factory installations). The compressor, the condenser, and the interconnecting tubing were under the bonnet.

Freon 12

Controlled electrically and driven by the fan pulley, the early style air-conditioners cooled the inside of the car through the unique qualities of Freon 12, a refrigerant which constantly circulated through the closed circuit of the system. Freon 12 was a liquid which boiled at 21.7 Fahrenheit / -29.83 Celcius below zero, but under pressure boiled from 80 to 90 Fahrenheit / 26.66 to 32.33 Celcius. The compressor, acting as pump, forced the Freon in liquid form to the expansion valve. This valve permitted the liquid to expand and cool as pressure was released, and the boiling point then dropped to between 10 and 30 F. When this happened, the liquid changed to a very cold gas, which passed through the evaporator tubing.

Warm air in the car was blown or pulled through the gas-chilled fins and tubes of the evaporator. The heat in the air was transferred to the Freon, which carried the heat to the condenser where cooler outside air dropped the gas temperature so it again became a liquid. This process was repeated over and over as a continuous cycle.

Cooling, with these early air-conditioners and with the new, occurred as heat inside the car was passed on to the sealed-in Freon gas. Like moisture on cold windows in the winter, the cold evaporator coils and fins condensed humidity out of the air (into water), which was then drained off - or in some cases, allowed to drip into the passenger foot-well. There was also a cleaning effect going on here, because pollen and dust were trapped on the moist evaporator coils.

Types of After Market Air-Conditioner

By 1972 air-conditioning installation had been pretty much perfected, such that iw was possible to get an air conditioner installed in three to five hours. Units could be placed in the car's boot, with cool air outlets coming out the rear-seat package shelf. The most popular style, however was the the custom under-dash variety, where the evaporator was centrally mounted. Spend a little more and you could get a sleek custom unit where about all you could see was the cool air outlets and the control panel. Other units were built-in at the factories and required no special installation.

In America, many of the independently manufactured units could not be differentiated from factory-installed ones. Styling and new designs enabled the custom units to be completely built-in, doing away with centrally mounted evaporators. The remaining units that were centrally mounted were generally so well slimmed down and modified that, by 1978, they no longer took up vital space. Obviously the custom units were installed after the car was made, thus all parts were accessible for maintenance. In addition, when it came time to sell the car, you could take out the custom unit and re-install it on your next vehicle - although this was much more a sales ploy than a realistic option (but we have no doubt some owners actually did this).

There was other major differences that affected performance. Factory fitted air-con units from the 1960s and 1970s generally had their evaporator coils inside the engine compartment, while the custom units had theirs inside the passenger compartment behind the firewall. Since the evaporator was what removed heat and gave cooling, it logically followed that an evaporator mounted in the engine compartment had a huge extra heat load to battle besides that in the passenger compartment. Then as today, it is not uncommon for under-bonnet temperatures to reach 149 Celcius in many areas of the country.

Helping the Air-Conditioner Do It's Job

Owners quickly learnt that their air-conditioning unit gave better performance if they applied window-tint. Tint can reduce the heat load by as much as 15 percent. Another obvious thing to do, particulary on older model cars, was to insulate the headliner. And of course there were a few disadvantages - a car with air conditioning gave slightly less mileage, especially on the low-horsepower cars - where the hit to performance was more noticeable too. Servicing and maintenance was required too, however after market units were considerably less to maintain - the cost for example of a compressor being roughly double for a factory fitted unit to that of an after-market version.

But on the down side, owners of after-market systems usually had to get their units serviced at specific centres, and there were generally far fewer of these than car dealerships. Wise owners from this era would ask to see a list of the manufacturer's service locations countrywide, because most (if not all) gave their customers a list of approved repair and service shops across the nation. The reason this was important was because the air-conditioning unit involved refrigeration as well as mechanics.

Why Air-Conditioners Continue To Work Hard

Why an air-conditioner has to continue to work hard after you have got rid of the hot air is pretty obvious. There is still the heat of the metal, glass, and upholstery to cool off before you get the full benefit of air conditioning. Even today, there is no air conditioner made that can cool off such objects completely until the unit has been in operation for at least 45 minutes. Stating the bleeding obvious, to eliminate the problem of stored heat in a car, just remember to park in the shade.

If you drive a classic car (and you should do, if you are on the Unique Cars and Parts site) there is some good news should your classic be fitted with an older style custom units. Unlike some factory air conditioners from the era, the after-market jobs could be used in the winter at the same time you used the heater. In this way they dried the air out on damp or rainy days, eliminating fogged windows. This way you could have only a slight amount of cooling, while the heater controls the actual temperature. You will no doubt be familar with this on your daily drive - but older cars were not so easy to live with.

Should you with to add an air-conditioner to your older classic car, remember that there were a great variety of styles and models to choose from from 1963 on (and particularly with American cars). Virtually all reputable units were excellent in quality - however you would need to ensure the cfm (cubic feet per minute) or BTU (British thermal unit) capacity was up to the job of cooling your car.
Auto Car Air Conditioning Installation
The typical setup of an after-market air-conditioner from the early 1970s. A is the condensor, B the Pump or Compressor, C the Evaporator or Fan Unit.
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