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Smart Home

What to do when your AC won't cool

Here's how to keep your cool before calling a repairman.

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Simple fixes can help when you're AC is on the fritz.

Tyler Lizenby/CNET

It's 90 degrees outside and you need a break from the heat. The thermostat is set to 65, but your home feels like 80. And then you realize something's wrong with the air conditioner.

No need to panic. Luckily, whether you have central air conditioning or a window unit, there are a few ways you can troubleshoot cooling problems without calling the repairman. Don't worry, these don't require you to do anything dangerous or technical. They're simple fixes anyone can try.

Change the filter

Problem: Your room or house takes longer than usual to cool down.

Fix: It's probably time to clean or change the air filter on your air conditioner, depending whether you have a reusable or disposable filter. 

Remove the filter (you may need to check the AC's manual to find it) and hold it up to the light. If you can't see light shining through it, then it's clogged with dust. This inhibits air flow, making your unit work less efficiently.

If you have a disposable filter, simply switch it out with a new one. If it's a washable filter (again, check your manual), fill a tub with a few inches of warm water and a couple drops of mild dishwashing liquid. Let the filter soak for 10 minutes, then rinse it well with clean water. Shake the excess water from the filter, and then let it air dry before reinstalling it.

See if the unit is frozen

Problem: Your AC unit is blowing air, but it's room temperature or warm and the room won't get cool. 

Fix: Sometimes when an air conditioner runs nonstop to keep up with the heat, the evaporator coil freezes over. Put your hand on the side of the unit near where the filter is. If it feels very cold, then it's probably frozen inside. You may even see ice hanging off the unit. 

Turn off the cooling mode and turn on the fan to let the evaporator coils defrost. While you're at it, be sure that the filter and the coils around the filter are dust-free. Dust can make an AC unit freeze over, too.

Defrosting can take a few hours, so you may want to go out to a movie or head to the mall while you wait. 

Very important: Do not use your air conditioner on the cool setting if you suspect it is frozen over. This can ruin the compressor (an important component), leading to expensive repairs. Again, either turn on the fan only or turn the whole unit off until the ice melts.

Check the vents

Problem: You have central air and one room isn't getting cool, but the others are.

Fix: This may seem obvious, but check the vents in the room, especially if they're on the floor. Debris may have fallen in and blocked the air passage, or a toddler may have stuffed play clay down in vent (it's happened). Either way, unscrew the vent plate and scoop out anything that may block the flow of air. 

Give it a wash

Problem: You've tried all these fixes and the AC still isn't cooling properly.

Fix: The outside vents may be clogged up. Unplug the window unit or shut off the circuit breaker for your outdoor unit. Spray the part of the unit that is outside the window or by your house with a water hose to wash off any dirt, leaves or bug carcasses that may be blocking air flow. You can also use a large cleaning brush to sweep debris from the grates.

Call in the professionals

If none of these solutions are helping, it's time to call in the professionals. You don't want to damage your air conditioner or cause serious, costly issues in an effort to stay cool.

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