An AC register.

Once you get your air conditioner running again for the first stretch of the season, you may ask yourself: Hey, is it working as well as it used to? Better to address that question before temperatures rise from swell to sweltering.

Like any appliance, air conditioners need a little TLC to deliver optimal performance. It’s the ACs that haven’t been kept in top-notch condition that tend to struggle most in hot weather.

More on Air Conditioning

To make sure you don’t sweat the next heat wave, we asked the experts at Consumer Reports and air conditioner pros to identify the most common problems that crop up with window and central air conditioners. They highlighted eight problems to troubleshoot now.

The No. 1 problem affects both window units and central AC systems, and—we’re happy to report—its the easiest to fix. Here are eight questions to ask that will help you keep your AC in peak performance all summer long.

1. Is the Filter Dirty?
No matter which type of air conditioner you have, a clogged filter restricts airflow, decreasing efficiency and reducing the ability to effectively cool the air. If you haven’t cleaned the filter in your window or portable air conditioner recently, make sure you do and then check it periodically. Filters on central AC systems should be changed at least once a month, especially if your system is running constantly or if you have pets. “When we get calls about central air units that aren’t working well, 9 times out of 10 it’s because of a dirty filter,” says Stewart Unsdorfer, owner of Central Heating & Air Conditioning in Cleveland.

Window AC Checklist

2. Is It Too Sunny Inside?
If your window AC is in a window that gets direct sunlight in the heat of the day, it’ll have to work harder to cool your space. If you have a choice, move it to a shadier spot. If not, keep your shades and curtains drawn during the day to block the sun and prevent it from heating up your house. Same goes if you have Central AC.

3. Is Warm Air Leaking In?
Check the seals around your window AC to make sure hot air isn’t getting in (or cold air isn’t seeping out). Reseal around your unit with weatherstripping if necessary.

“Most new window units come with insulation panels to place over the plastic adjustable side panels,” says Chris Regan, CR’s senior air conditioner tester. “But to maximize efficiency, you’ll still need to use weatherstripping around the perimeter of the unit. And always use the manufacturer’s installation and safety hardware.”

4. Is Your Window AC Vibrating?
Air conditioners make plenty of noise, including from the whir of the fan and the sound of the compressor cycling on and off. These noises are normal. But if you hear a vibrating noise, it may mean that your unit was installed incorrectly. Make sure it’s sitting securely in the window and review the installation instructions in your owner’s manual to confirm that no steps were missed.

Central AC Checklist

5. Is the Thermostat on the Right Setting?
With a smart or programmable thermostat, you can more easily control the temperature in your home so that it’s at a comfortable temperature when you’re there and a bit higher when you’re not. If the temperature seems off, make sure the thermostat isn’t exposed to direct sunlight, which may cause it to register the wrong temperature.  

6. Are the Registers Dirty or Blocked?
If you have a forced-air heating and cooling system, regularly vacuum the registers to remove any dust buildup. Make sure that furniture and other objects aren’t blocking the airflow through your registers.

7. Are Plants Crowding the Compressor?
The outdoor compressor for central air needs adequate airflow to work correctly, so make sure there’s at least 2 to 3 feet of space between the compressor and any plants or structures. There should also be 5 feet of clearance between the top of the unit and any trees above.

8. Did You Remember the Annual Checkup?
An inspection by an HVAC (heating, ventilation, and air conditioning) technician can catch any serious problems before they get worse and leave you hot and bothered at the peak of summer. The technician will check all the moving parts, as well as the refrigerant, and recharge the system if necessary.

Need a New AC?

If your room air conditioner is beyond repair, you can find one that did well in our tests for as little as $150 for a small unit and as much as $470 for a large one. Make sure you match the size of the air conditioner to the room it’s meant to cool. Below, models in each size that performed well in CR’s tests. You can find more in our full air conditioner ratings and recommendations.

ACs for Small Rooms (100 to 300 square feet)

For a small bedroom, home office, or guest room, look for an air conditioner with a capacity of 5,000 to 6,500 Btu. You’ll want one with good scores for comfort and noise. Here are three top picks to consider.

Top Picks

1

Comfort
Brownout
Indoor noise high

2

Comfort
Brownout
Indoor noise high
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ACs for Midsized Rooms (250 to 400 square feet)

To cool a bigger or busier room, you’ll want to step up to a midsized air conditioner rated at 7,000 to 8,500 Btu. If it’s for a bedroom, heed our noise scores. Here are three top picks.

Top Picks

1

Comfort
Brownout
Indoor noise high

2

Comfort
Brownout
Indoor noise high
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ACs for Large Rooms (350 to 650 square feet)

For a living room or family room, you’ll want a large air conditioner, 9,800 to 12,500 Btu, especially if you have an open floor plan. Here are three good choices.

Top Picks

1

Comfort
Brownout
Indoor noise high

2

Comfort
Brownout
Indoor noise high
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