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No cold air? No sweat. Try diagnosing the problem on your own and you could be well on your way to cool runnings in no time.

Nothing compares to the feeling of a cool breeze streaming from an air conditioner on a sweltering summer day -- or the devastation of one that decides to go kaput just when you need it most. Air conditioners can be pretty time-consuming and costly to repair (professionally or on your own) -- and even more wallet-draining to replace.

The best defense is to address problems as soon as they arise. Even if there's just a hint that your window or central air unit isn't performing up to par, look into it immediately. If the difference between the outdoor and indoor temperatures is 15 degrees or more, then nothing is probably awry. But if the disparity is higher, you'll want to take action.

Window air conditioning units sit on the sill and are smaller than both a split air conditioning units and central air conditioning units, and are designed to cool a designated area. Unfortunately, you're pretty limited in the scope of work you can do on a window unit. Unfortunately, most window A/Cs aren't designed to be taken apart and fixed, but instead used and tossed after a few seasons. Still, there are some things you could try.

Common cause #1: Dirt is gumming up the works.
Grime. Dust. Crud. Whatever you call it, it's definitely the bane of any window unit's existence, as it hinders the efficiency of its essential components. First, unplug the unit and tackle the filter. If your A/C has a dirty filter, chances are it also has a dirty evaporator coil. Dirt reduces airflow to the coil and insulates it, thereby reducing its ability to absorb heat. So slide out the insert (you may need to remove the front grille to gain access) and wash it in the sink (if it's disposable, replace it) with soap and water, then rinse and let dry completely before putting it back in place. For optimal performance, repeat this once a month.

Common cause #2: Buckled condenser fins.
Because they're made of fine-gauge aluminum, the fins that make up the condenser coil (where Freon gas travels through, absorbs heat, and cools the air) often bend and can prevent air from properly being drawn out of the unit. In this case, use a fin comb, which has ultra-thin tines designed to fit between smashed fins, to straighten them as best you can.

Common cause #3: It's working too hard.
If your unit is near a heat source (i.e. someone else's unit or a huge TV), or if it's surrounded by thick vegetation and isn't given ample space for proper air circulation, it's simply not going to work as well as it should because it's being forced to work overtime. According to This Old House plumbing and heating expert Richard Trethewey, you should "install window units on the north or east side of your house, or build a screen to shield [it] from the sun. Putting [it] in direct sunlight reduces efficiency by as much as 10 percent."

Thinking of hiring out the fix? Generally, it's never worth the expense of having a window unit serviced even if you think it might be salvageable, as house calls will cost you at least $100 -- and that's excluding parts and labor. If your unit fails within the first couple months of its purchase, it's probably covered by the manufacturer's warranty, and you should be entitled to a replacement. Our advice? If the A/C is already few years old and none of these tricks work, give it the old heave-ho and opt for a new Energy Star-qualified unit.

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First, a quick primer: split systems and central air systems work exactly the same way: both have outdoor condensers and indoor evaporators. Split systems don't, however, have ductwork like central air, are smaller, and generally cool one room as opposed to the whole home.

Common cause #1: Yup, it's dirt. Again.
First, always switch off the breaker next to the unit before you begin any work. Split systems tend to have removable filters that should be washed in the sink with soap and water. Central air filters should be disposed of and replaced monthly. In both systems, unscrew the outer housing and inspect the condensing unit for obstructions such as grass clippings, leaves, and other debris that could be blocking airflow. Gently clear debris from coils and aluminum fins with a soft brush and replace the housing. (Also, check the condenser fins for signs of buckling and straighten them out, too.) It's also important that the condenser have at least 24 inches of unfettered breathing room for the unit to run efficiently, and to prevent the fan from overheating, and thus the motor from breaking down.

Common cause #2: Leaky ductwork.
So your central system is definitely running but the house isn't cooling off? Air could be escaping through gaps in ceiling ducts. Head up to the attic to check for leaks; hold up a lit incense stick next elbow joints and seams. If you see plumes of smoke being pulled toward, or pushed away from, the duct you have a leak that needs sealing. Carefully seal all openings with thermal mastic duct tape and that should solve the problem.

Common cause #3: Low Freon levels.

When you've ruled out other more obvious culprits like dirt and air leaks, it may be time to consider whether the refrigerant Freon is slowly leaking out of your unit. Look at the two copper lines extending out of the back of your condensing unit: the thicker of the two lines should have a round glass indicator showing a colored dot within. If the dot appears green or yellow, your Freon level is adequate. If the dot is red and liquid appears to be bubbling from underneath the glass, you probably have a leak, and it's time to call a pro. Since Freon gas is strictly regulated by the EPA, no one but a licensed pro can handle it.

Do you have any experience with your own DIY air conditioning fixes? Tell us here!

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