Solved! What to Do if Your Air Conditioner Is Not Cooling Your Space

Don’t sweat it if your central air conditioning won't blow cold air. Learn the most common causes of an AC that won't cool, and easy ways to troubleshoot the problems yourself.

By Theresa Clement and Bob Vila | Updated Jan 24, 2022 11:29 AM

air conditioner not cooling

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Q: I’ve just turned on the air conditioner for the summer, but I just can’t get get comfortable. The appliance circulates air, but it is not blowing cold air. Why is my air conditioner not cooling? More important, how can I fix it?

A: It’s the last thing you want on a sweltering summer’s day—a central air conditioner not blowing cold air. While your first reaction may be to contact an HVAC pro, with a little of your own troubleshooting, you might remedy the problem and save on a costly house call.

Air conditioning systems operate on a basic scientific process called “phase conversion.”

  1. Refrigerant, the liquid used in an AC system, undergoes a continuous cycle of evaporation and condensation within the unit’s sealed coil system.
  2. The unit’s evaporative coils (usually located inside your home near a blower unit) become icy cold as the refrigerant within turns from a liquid to a gas.
  3. The unit’s fan blows air over those icy coils, which forces cooled air through your home’s ducting.
  4. The gas then cycles back to a condenser coil unit (located outside) where it cools back down to a liquid and the cycle repeats itself over and over.

If your AC system is blowing warm air, several culprits may be to blame. The following are a few things to check when your air conditioner is not cooling your space.

air conditioner not cooling

Check and reset the thermostat.

It may seem simple, but sometimes when an air conditioner is working but not cooling it is simply the result of someone switching the thermostat from “Automatic” to “Fan.”

When the switch is set to “Automatic,” the thermostat switches on the air conditioning when the indoor temperature rises above the desired preset temperature. If the switch was accidentally set to “Fan,” the unit will blow air through the duct system, but no cooling will take place.

Easy DIY Fix: Check and reset the switch from “Fan” to “Automatic.”

Replace the dirty filter.

If it’s been more than a couple of months since you’ve replaced the return-air filters in your AC system, they may be clogged, dirty, and affecting air flow. When filters get clogged with animal fur and dust, the AC system can’t draw in sufficient air, and as a result, only a wimpy flow of air comes out.

Easy DIY Fix: Remove the return-air filter and, if you can’t see what’s on the other side, replace it. If you can see through the filter, your problem with your AC not cooling lies elsewhere.

air conditioner not cooling

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Clear the clogged condensation drain.

Air conditioners work in part by removing humidity from the air (through condensation), and that moisture must go somewhere. The job of a condensation drain hose is to direct water to a floor drain or to the outside of your home, depending on your system. Condensation drains are subject to blockage by mold and algae growth. When this happens, some AC won’t blow cold air while others will shut down completely.

Easy DIY Fix: Locate the end of the condensation drain line (it’s often in a utility room) and visually inspect it for clogs. If you see a clog, carefully clear it out with the end of a small screwdriver or similar narrow item.

If a clog forms higher in the line where you can’t physically reach it, suctioning on the end of the line will usually remove it. Use the hose on a wet/dry shop-type vacuum—and hold your hands around the opening—to create sufficient suction between the two hoses.

After removing a mold or algae clog, pour a couple of cups of white vinegar into the condensation pan that lies beneath the evaporator coils in the inside blower unit (learn how to access and identify the coils and the condensation pan below). The vinegar will kill residual mold buildup and reduce the risk of future clogs.

Try to diagnose duct malfunctions.

In a central AC system, the main blower forces cold air through the ducting and into individual rooms. If a duct somewhere between the blower and a room register (the grill that covers the opening of an HVAC duct) has broken, the cold air could be blowing out before it reaches the room’s register. If cool air is blowing from some registers but not from others, there’s a good chance the ducting that feeds the registers is at fault.

Easy DIY Fix: If you have an unfinished basement, you can examine the ductwork to see if a joint has come loose. If so, refit the ends of the joint and tape the new joint securely with duct tape. If a ducting joint has come loose within a finished wall, however, you won’t be able to easily locate it and will need to call an HVAC professional.

Clear the area around the compressor.

If dry leaves and debris have piled up next to the compressor unit, it may not be able to draw in sufficient air. To find out, locate the compressor unit, which will typically be tucked away on the back or the side of the house where it won’t draw attention.

Easy DIY Fix: Clean away all debris or anything else that might be crowding the unit, such as weeds or overgrown vines. For peak functioning, don’t place anything on top of the compressor.

Clean dirty coils.

If your air conditioner is working but not cooling, dirty coils may be the culprit. The typical AC system has two sets of coils: condenser coils, which are located in the outside compressor unit and evaporator coils, which are encased near the indoor blower unit. When either set of coils becomes dirty or covered with mold and debris, cold air output can suffer. Cleaning the coils involves removing the metal enclosures that protect them.

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Easy DIY Fix: If you don’t feel comfortable opening the AC units you can ask a pro to clean them. If you’d like to try cleaning the coils on your own, however, follow these steps:

  1. Shut off the power to both the exterior and interior units at the breaker panel. Each one will be on a separate breaker.
  2. Follow the AC manufacturer’s directions for removing the exterior compressor cage or the metal panels that house the evaporator coils.
  3. To clean interior (evaporator) coils, spray a non-rinse evaporator coil cleaner such as Nu-Calgon Evap Foam No Rinse onto the coils, which resemble U-shaped copper or steel tubes. The non-rinse cleaner foams up on the coils and dissolves dirt and grime before liquefying and running into a condensation pan that empties into the condensation drain hose.
  4. To clean exterior (condenser) coils, spray the coils, and the thin metal fins that surround them, with a condenser coil cleaner such as Nu Calgon’s Nu Blast Condenser Coil Cleaner. This cleaner is different from evaporator coil cleaner and it will require rinsing with the hose. Follow the product directions carefully.

Know when it’s time to call a HVAC pro.

If you’ve gone through the above DIY steps and your AC system is still not cooling, the problem could be leaking refrigerant (Freon) or a failed compressor unit. Freon is federally regulated and may only be handled by a licensed HVAC professional. If the AC not blowing cold air is the issue and your AC system is more than 10 years old, you may have a failed compressor and need to purchase a new system. These issues can only be addressed by the pros, so make the call!

Final Thoughts

When an AC unit is not blowing cold air, there are many possible causes that can be easily fixed without the help of a professional. From changing the filter to checking the settings to cleaning the coils, it’s possible to get your air conditioner working again quickly and keep your home cool. However, if you’ve tried all of the air conditioner troubleshooting and DIY fixes, and it’s still not working, it’s time to call an HVAC professional for an evaluation.

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FAQs About What to Do if the AC Won’t Blow Cold Air

After following the above troubleshooting steps, you may still be wondering, “Why is my AC not working?” or “Why is my AC not cooling?” An air conditioner not working is frustrating, so we have answered some of the most popular questions about an AC not working below.

Q: Should I turn off the AC if it’s not cooling?

Turning off the AC is usually helpful and sometimes required to safely investigate some of the possible issues with an AC system not cooling. If it’s a thermostat setting that’s the issue, it’s not necessary to turn off the AC.

Q: Why is my AC blowing cold air but not cooling the house?

If the air conditioner is blowing cold air but not cooling the house, there could be a leak in the home to the outside. Check that all of the windows and doors are closed. If the air feels cooler than the room temperature, it may not actually be the desired temperature and could be just the fan blowing.

Q: How do I know if my AC compressor is bad?

If the blowing air is warm or there are loud noises or vibrations when starting the air conditioner, then the compressor may be going bad.

Q: How do I reset my air conditioner?

First turn off the power to the air conditioner at the breaker panel, then press the reset button on the unit for a few seconds, and lastly turn the unit back on. Check the user’s manual for the particular unit for specific instructions.

Q: How long does it take for an AC unit to reset?

Most experts recommend waiting about 30 minutes after pushing the reset button before turning the unit back on.

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