Manufacture and use of greenhouse gases are the largest environmental impacts of air conditioner use

The electricity produced to power air conditioning brings both global and personal health consequences. In burning fossil fuels like coal to supply electricity to homes and workplaces, power plants release clouds of soot and other pollutants into the environment, including mercury and carbon dioxide (CO2). Air conditioner use in the United States results in an average of about 100 million tons of CO2 emissions from power plants annually.

Ozone-depleting chlorofluorocarbons (CFCs) which was used as cooling agents in the past have been substituted with hydrochlorofluorocarbons (HCFCs) which deplete 95 percent less ozone. However, increasing demand for air conditioners in hot climates like India and China has amplified the chemical's output in developing countries from 20 to 35 percent yearly, causing damage at an alarming rate and possibly setting back ozone recovery by 25 years. In industrial countries, HCFCs are substituted with ozone-safe cooling agents and was banned in the United States in 2010. But HCFCs is allowed in developing countries through 2040, and since they're still cheaper to use than ozone-safe chemicals, production in developing countries has increased fivefold until 2010.

For conscientious disposal, federal law obliges that HCFCs be retrieved from air conditioners and other appliances before they are dismantled for recycling or tossed in landfills, and the Environment Protection Agency (EPA) is authorized to impose fines of up to $25,000 for failure to conform with regulations.

In the midst of scorching heat waves, air conditioning serves as a lifesaver, defending against heat stroke and hyrthermia. However, without suitable maintenance, air conditioners can also be a health hazard. Dirty filters can allow allergens, pesticides and other particulate matter to go into one’s home from the outside, posing threats to indoor air quality. Exposure to these pollutants can trigger a host of health problems, including allergies and asthma and eye, nose and throat irritation.

Reference:

Air Conditioner Buying Guide, http://environment.nationalgeographic.com/environment/green-guide/buying-guide/air-conditioner/environmental-impact/