We humans are finicky. We like the air around us to be comfortable  not too hot, not too cold.

Although we have no say about the outside temperature, we definitely take control of the inside temperature. We heat our houses in the winter when it’s cold outside and cool them during the summer when the outdoor air is too hot and humid. It is only during brief periods in spring and fall that we are content with things just as they are.

The air conditioner sitting outside the home or in a window is a great invention for keeping us comfortable in the summer. It does so through the use of mechanical and electronic components that transfer heat from the house to the outdoors and circulate cool air.

Homeowners can do a lot to keep their air conditioner in good running order.

“Clean the outdoor unit with a hose, especially when the cottonwoods go to seed,” said Helen Cox of SRH Mechanical Contractors Inc. of Lawrence.

The water sprays away dust, sand, leaves and other debris that may cause the unit to work inefficiently. Even a small film of dust can decrease efficiency by 5 percent to 50 percent.

Resist the urge to camouflage the outdoor unit with shrubs or solid fences, Cox said. When these are placed too close to the air conditioner, they may restrict air flow.

Go with the flow

Regular maintenance will help the air conditioner’s performance, she said.

“One of the most common mistakes is that people don’t change the furnace filter often enough,” she said.

How often is often enough?

“It depends on how dusty your home is,” Cox said. “Certainly more than twice a year.”

Consider changing the filter even once a month if you have pets. A dirty furnace filter limits air flow and makes the unit work harder than it would with a clean filter.

Another bit of advice from Cox: “Once you turn it on, you should leave it on.”

Because the air conditioner dehumidifies the air and then cools it, turning the unit off periodically to save money is counterproductive. With the air conditioner off, humidity returns. When the unit is turned back on, it must start over to remove moisture from the air and cool it.

“You’re better off to leave it at a higher temperature,” she said.

Some warm-weather holdouts wait until the Fourth of July to turn on their air conditioners, Cox said. But using the unit for the first time on a holiday is not a good idea. If something goes wrong and requires a service call, well, that’s going to be big bucks.

It’s better to prepare, she said. Spring is a good time to have the air conditioner inspected and serviced.

“You need to have it relatively warm outside  60 degrees or better,” Cox said.

An early air conditioner check will help uncover problems like a leak in your line or a faulty condenser motor, she said. Repairs can be done before the heat of summer sets in, when an air conditioner becomes more of a necessity.

Among other things, the professional service person will clean the condenser coil, check for clogs in the evaporator coil, check the drain pan under the coil for proper drainage and identify if algae have built up.

Improving efficiency

According to a specialist at Niehoff Heating & Air Inc. of Lawrence, a well-maintained air conditioner should have a life expectancy of about 12 years. With little or no maintenance, units may last only five to eight years.

Those in the market for a new air conditioner should consider several things.

The first is a unit’s efficiency, known as its seasonal energy efficiency ratio.

Higher ratios are better. By 2003 the U.S. government will require a ratio of 13 for air conditioners.

Right now the lowest ratio for new air conditioners is 10. The best available ratio is about 18, while many older units have ratings of 6 or less. Most consumers should look for a ratio of 12 or higher when buying a new air conditioner.

For large two-story homes, a zone system or two air conditioners  one for each floor  might be your best bet.

“Your equipment is as good as the company that installed it,” Cox advises.

If you have problems with the unit, even if it is still under warranty, you’ll be better served by a qualified, reputable company.

 Carol Boncella is education coordinator at Lawrence Memorial Hospital and home and garden writer for the Journal-World.