Which car have the best air conditioning?
WITH daytime temperatures soaring above 38ºC (100ºF) on numerous occasions this past month, along with a relatively high humidity instead of southern California’s normal desert dryness, your correspondent has been reluctant to take either of his two old cars out for a spin. He built the elder of the pair back in temperate Britain in 1972 (its 40th birthday comes up this October) and gave no thought at the time to air conditioning. The younger one, bought in sunny California on a previous assignment, is now a mere 24 years old, and came, naturally enough, with factory-fitted air conditioning. Unfortunately, no cold, dry air issues forth from the vents these days.
An air-conditioning system, whether installed in a building or a motor car, is simply a large refrigerator, with an ice-box big enough to encompass the occupants. It works by taking advantage of the way heat is absorbed and released when a refrigerant changes its phase back and forth between liquid and vapour as a result of changes in pressure.
In a car, the refrigerant gas is first compressed, causing it to heat up as its pressure mounts. This hot gas is then pumped through a set of condenser coils where it dumps its heat acquired during compression along with the heat previously absorbed from the vehicle’s cabin—condensing into a liquid in the process. The refrigerant, now in liquid form, is next piped through an expansion valve which, like a nozzle, induces a sudden drop in pressure. This causes the liquid to atomise into a low-temperature gas.
The cold vapour is then pumped through a second set of coils in an evaporator unit inside the vehicle’s cabin. Because heat always flows from warmer to cooler regions, the cold gas absorbs heat from within the warm cabin, cooling the surrounding air in the process. The cycle then repeats itself...
Or so it would if the compressor worked properly, the condenser and evaporator were in fine fettle, the hoses and seals had no leaks, and the filter/dryer used to remove moisture and other impurities from the refrigerant and its oil supply was not clogged. One, or several, of these problems may be the reason why no cool air is wafting from the air-conditioning vents in your correspondent's 24-year-old car.
Being a 1988 model, the system fitted to the vehicle used R-12 (Freon-12) as its refrigerant—a chlorofluorocarbon that was phased out altogether in 1996 under the Montreal Protocol, an international agreement designed to protect the ozone layer in the upper atmosphere. Ever since, new cars have used a refrigerant known as R-134a, a tetrafluoroethane which, possessing no chlorine atoms, does not catalyse the conversion of ozone into oxygen.
Retrofit kits have existed for years for converting from R-12 to less harmful R-134a. For Californians with classic cars, the choice has been either to switch, or to drive down to Mexico where R-12 remains plentiful and cheap. Your correspondent opted some years back to have his system converted to R-134a.
Despite what suppliers say, R-134a is not a “drop-in replacement” for R-12. The conversion means changing not only the system’s refrigerant, but also replacing all the hoses, seals and service valves. Because of a difference in molecular size, R-134a can easily seep through pipework and joints designed for R-12. To do the job properly, the compressor, evaporator, filter/dryer and condenser have to be flushed clean of all traces of the lubricating mineral oil used in conjunction with R-12.
In your correspondent’s case, the conversion has been less than successful. By most accounts, R-134a is nowhere near as effective a refrigerant as R-12 anyway. Despite having new hoses and seals, as well as a thoroughly flushed system, he has never achieved anything like the cabin temperature he enjoyed previously.
Worse, the system works in a fashion for a month or so, and then packs up completely. Having had this happen twice now, he has stopped having it recharged. Though R-134a may be ozone friendly, it is still a pretty aggressive greenhouse gas, with a Global Warming Potential (GWP) of 1, 430—ie, 1, 430 times worse than carbon dioxide. Not the sort of stuff you want leaking into the atmosphere.
No amount of fluorescent dye added to the system in the workshop has detected the leak. Your correspondent can only assume a seal is failing intermittently, probably when the engine is hot while driving fast with the air-conditioning on full blast.
What to do next? Several fellow classic-car owners swear by a refrigerant known as R-414a, a blend of certain hydrochlorofluorocarbons and hydrocarbons. While not compatible with R-134a, it is said to be the nearest thing to a drop-in replacement for nasty old R-12. But, again, replacing the refrigerant means replacing the hoses with new ones that have special liners. Any leak would cause the components in the R-414a blend to seep out at different rates. The compressor could then fail from loss of lubricant.
In the circumstances, your correspondent would prefer to stick with R-134a—provided his leak could be traced and fixed. The only problem with doing so is that California is expected to ban the sale of R-134a (as Europe did in 2011) because of its potential for causing global warming.
SAE International (formerly the Society of Automotive Engineers) has proposed that R-134a be replaced by a new fluorocarbon known as HFO-1234yf. This tongue twister was formulated to meet the European Union’s latest requirement for an air-conditioning gas with a GWP below 150. HFO-1234yf has a GWP of just four—ie, 335 times less than the R-134a figure.
Though it is expensive, European carmakers reckon HFO-1234yf has the lowest overall switching cost among the various alternatives. Assuming a compatible lubricating oil can be chosen, it could become a “near drop-in replacement” for R-134a. A factory to make the stuff has been built jointly by Honeywell and DuPont, two American companies that own most of the patents. General Motors is to introduce the new refrigerant in its domestic models in 2013.