A: Heating and air conditioning companies often offer maintenance servicing for both air conditioning units and furnaces.

"We recommend annual air conditioning check-ups in the spring and furnace check-ups every fall. Although regular checkups will not absolutely guarantee that a unit will continue to work perfectly throughout the season, they will reveal most small problems that can lead to major, far more expensive problems if left unattended."

Homeowners can do the following things to maintain their air conditioning units:

1. The first thing to check before turning on your unit is to make sure the condensing unit located outside is not covered up. The unit needs to draw air into the system in order to have something to cool and circulate inside, but the process is hindered if it cannot pull in enough outside air. (We're amazed how many homeowners call because their air conditioner isn't cooling, only to find they forgot they had temporarily stacked lawn furniture, bags of leaves and lawn clippings, around their unit over the winter.)
2. Some people intentionally cover their condenser to protect it from the elements during the winter, although these units require no protection since they are designed for outdoor installation.
3. Run your air conditioner for a few minutes in late spring or early summer, before you need it. If you wait until the first hot day to discover it isn't working, you'll find yourself on a waiting list, sweltering for days before an air conditioning specialist can come to fix it.
4. Change the filters regularly. Dirty filters restrict air flow, reduce efficiency and worse case, can cause the evaporator to ice up. Disposable fiberglass filters should be replaced. Electrostatic or electronic filters need to be washed regularly.
5. Be sure all access panels are secure, with all the screws in place.
6. Clean obvious obstructions such as newspaper and leaves from around the exterior of the unit.
7. Be sure the thermostat is set in the cooling mode. Just setting the dial below room temperature will not activate the air conditioning if it is set in the heat mode.
8. A thoroughly cleaned air conditioning unit will operate at top efficiency. However, homeowners are strongly discouraged from using a hose and water to try to clean it themselves because of the very serious risk of electrical shock and possible shorting of electrical components.

While you're at it, here are the steps of a professional furnace check-up.

1. Inspect thermostat for proper operation.
2. Inspect filter, and change or clean as needed.
3. Check all electrical components and controls.
4. Oil motors as needed.
5. Inspect heat exchanger for possible cracks. A crack in the heat exchanger will introduce carbon monoxide into the living space.
6. Check air flow. If diminished, it may be necessary to clean the evaporator coil.
7. Check air fuel mixture, where appropriate.

To locate a reliable Heating & Air specialist to service your air conditioning unit, visit Home Advisor, and be matched with the ideal service professional in your area.

by Kathy Maynard, reprinted courtesy of HomeAdvisor.com