I’ve been told that automobile air conditioners are bad for the environment.

I’ve been told that automobile air conditioners are bad for the environment. Exactly why and what part of the air conditioner is bad?

—Susan Vogel, Somerville, NJ

The harmful effects of automobile air conditioners can be directly attributed to leaking of CFC R-12, one of a number of cooling ingredients patented by DuPont and popularly known as Freon. In December 1995, the U.S. banned the manufacture of this ozone-depleting chlorofluorocarbon (CFC) in order to adhere to standards set by the Montreal Protocol, an international treaty phasing out the production of such chemicals. But existing stockpiles of the gas—and pre-1994 autos that still use it—could keep its toxic legacy around for years.

The cooling ingredient HFC134A, also known as tetrafluoroethane, has since replaced CFC R-12 as the main cooling ingredient in car air conditioners. But while HFC134A does not contribute to ozone depletion and is a more eco-friendly choice than R-12, it is a gas that contributes to global warming. In fact, because of this, the European Union has slated a phase-out of HFC134A to begin in 2011 and be completed by 2017, despite the fact that alternatives are still only in experimental phases of development.

Owners of pre-1994 automobiles can spend a few hundred dollars to modify their air conditioners to use HFC134A, though the Environmental Protection Agency (EPA) cautions that not all systems designed for R-12 work as well using HFC134A and recommends such conversions only on cars made after 1980.

When air conditioners in cars that use CFC R-12 are being refilled or repaired, federal regulations require that the service shops recycle the refrigerant instead of releasing it into the air. Regulations also require that the refrigerant be removed from vehicles that are scrapped or have been abandoned. The refrigerant is then filtered so that it can be reused.

If the refrigerant in your vehicle”s air conditioning system needs to be replenished, always have a professional do it. You can damage your system if you improperly change it yourself, and only certified mechanics can legally purchase refill cans of CFC R-12. Additionally, if your air conditioning system is leaking refrigerant, have it repaired—don’t just refill it. This will both protect the environment and save you money in the long run.

There are other environmental considerations with auto air-conditioners, such as energy use. In an attempt to reduce the amount of energy car air conditioners use, Toyota has created a lightweight compressor—the heart of the air-conditioner—that consumes 60 percent less fuel.

Of course, the most environmentally sound and cheapest way to cool your car is to open your windows and let in the fresh air. According to the National Safety Council”s Safety and Health Policy Center, driving without using the car”s air conditioning increases fuel efficiency by about 2.5 miles per gallon.

CONTACTS: EPA Motor Vehicle Air Conditioning, www.epa.gov/ozone/title6/609; Toyota Air Conditioning Compressor, www.toyota-industries.com/environment/product/compressor.html; National Safety Council”s Safety and Health Policy Center, www.nsc.org/ehc.htm .