Why Is My Air Conditioner Not Cooling? Try These 6 DIY Fixes

Is your air conditioner not cooling your house like you think it should? Do you continuously turn the thermostat down, but your home still feels warm and muggy? If so, there may be a problem with your air conditioner. 

No one likes to hear there may be an issue with a major appliance like an air conditioner. The result is usually a costly repair bill or an expensive replacement. Before you call an HVAC technician who will charge you just to come to your home or purchase a brand new air conditioner, try these six DIY fixes to see if you can resolve the problem and save yourself some money.

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Why Is My AC Not Cooling?

If your AC is not cooling your home, it could be caused by various things including an issue with the thermostat, the air filter, refrigerant, coils, condenser, or compressor. You can address many of these issues yourself, but some will require the help of an HVAC technician. 

There’s an Issue with the Thermostat

Your thermostat regulates the temperature of the room through a sensor. When the room temperature is above the set temperature, the thermostat signals the air conditioner’s compressor to begin the cooling cycle. The thermostat signals the compressor to shut off when the room reaches the set temperature. 

If your AC is not cooling your home, it could be one of several possible issues related to the thermostat. Luckily, thermostat issues are usually easy to fix. First, check the thermostat’s settings. The on/off switch should be set to “cool,” not “heat.” Also, check the fan switch; it should be switched to “auto,” not “on.” 

Make sure the temperature is set to the correct temperature. It is possible that someone in the house turned the temperature up. You could also try turning the temperature down a few degrees to see if the AC turns on. If it turns on, check if the air from the vents is cool. If the air is warm, there is likely a problem with the AC unit itself. 

If the thermostat’s settings are correct and your AC is still not cooling your home, you can try a few other things before calling an HVAC technician. The thermostat might need new batteries or to be replaced. If it is a newer smart thermostat, try doing a hard restart. 

Also, consider the location of the thermostat. Does it get direct sunlight? Is it near appliances or electronics that emit heat like a stove or a television? These things can affect the thermostat’s functioning. A thermostat near a heat source or in sunlight will turn on more often as it attempts to cool your home. This excessive running of the AC unit may strain it and cause it to break down. 

The Air Filter Is Dirty

Most air conditioners have an air filter in or around the indoor air handler unit to trap contaminants like dust, pollen, and pet hair. The airflow is restricted when the filter becomes clogged with pollutants, and your home may be less cool. A dirty air filter can also cause more significant problems with your AC unit down the line. How often to change an air filter depends on a few crucial factors. Air filters should be replaced regularly to keep the air in your home clean and your system running smoothly. 

To check the filter to see if it is dirty:

  1. Shut off the air conditioner unit at the thermostat or the switch on or near the indoor air handler unit.
  2. Remove the filter from the unit’s cabinet. If you can see through the filter, it is clean and does not need to be changed.
  3. If you cannot see through it or if it has been more than three months since the filter has been changed, replace it with a new filter. 

The Refrigerant Is Low or Leaking

An AC unit contains a refrigerant that cools the warm air drawn from the home. If the refrigerant leaks  due to damage or vandalism, the amount of refrigerant in the unit will be insufficient to properly cool the warm air before releasing it back into the house. The unit will run more often as it tries to cool the home to the set temperature. A refrigerant leak could lead to more serious and expensive problems, such as a failed compressor. 

If you suspect a Freon leak, you must contact an HVAC technician since only licensed professionals can handle refrigerants. A refrigerant leak should not be ignored. Leaking refrigerant is bad for the environment and can cause symptoms in people and pets if the leak is indoors, although this is rare. Refrigerants such as Freon are gasses that quickly dissipate into the air. You will unlikely experience any symptoms unless you sit near the leak for a prolonged period. Actual refrigerant poisoning is only sustained when refrigerants are intentionally inhaled or leak into small, unventilated rooms. Still, you should immediately contact a technician if you find or suspect a refrigerant leak.

The Coils Are Frozen or Dirty

Your AC unit likely has two coils–a condenser coil in the outside compressor unit and an evaporator coil in the inside blower unit. The outdoor condenser coil is located behind the unit's thin metal fins. The job of the condenser coil is to release the warm air from your home with the help of the condenser fan. The evaporator coil is usually in the furnace's AC cabinet.  The evaporator coil's job is to remove heat and humidity from the air inside your home. 

Coils can become dirty or moldy over time. You can clean the coils yourself, but it involves opening up the units. If you don’t feel comfortable doing this, it is best to contact an HVAC technician. To clean the coils yourself, you must first shut off the power to the breaker's indoor and outdoor units. Remove the metal cage surrounding the outdoor unit. The condenser coil can be carefully vacuumed with a brush attachment, rinsed with a hose, or cleaned with a condenser coil cleaner. To clean the indoor evaporator coils, remove the panels of the indoor unit. The evaporator coils can be cleaned with a no-rinse evaporator coil cleaner. 

Usually, it is a sign of a refrigerant leak if both coils freeze. If there is frost on copper refrigerant tubing coming from the indoor unit, the outdoor unit, or if there is an excessive amount of condensate drainage near the indoor unit, you likely have a refrigerant leak. An AC unit low on refrigerant will not be able to cool your home adequately. If your AC is freezing up, contact an HVAC technician right away. Refrigerant leaks are a serious problem, and only licensed technicians may handle refrigerants.  

The Condenser Is Blocked

As discussed in the section above, your AC unit has a condenser coil in the outside unit. Sometimes the coil can become blocked by outdoor debris. Clogged coils affect the unit's ability to draw air and reduce the cool air from the vents. 

Check your outdoor unit for leaves lodged in the metal fins and clear them away. Shrubs, weeds, grasses, and vines growing close to the unit can also block the condenser’s airflow. Trim away branches and remove grass and weeds so the unit has unrestricted airflow. Make sure there is nothing placed on top of the compressor. Turn off the power to the unit and straighten any bent fins with a butter knife, but do not insert the knife more than half an inch.

The Compressor Is Damaged

The compressor is the core of your AC unit. It circulates the refrigerant between the outdoor and indoor units. If the compressor is damaged, the unit won’t be able to to cool your home properly. If the A/C compressor is not turning on, it may be damaged. The compressor may also be damaged if warm air is coming from your vents or if the compressor is making a loud noise such as buzzing or vibrating excessively when starting up.

Unfortunately, the best way to determine if the compressor is damaged is to replace it. Compressors are expensive, so replacing the entire unit may be preferable if it’s not still under warranty. Don’t despair; it’s still possible that the problem is not the compressor and some less-expensive electrical part needs to be replaced. Contact an HVAC technician to diagnose the problem before shelling out money for parts or a new system.

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Why Is My Air Conditioner Not Cooling? When to Call an HVAC Professional

If you have ruled out thermostat issues, a dirty air filter, dirty coils, blocked coils, and a damaged compressor, or if you’ve discovered frozen coils or suspect a refrigerant leak, it is time to contact an HVAC technician.

Although only licensed technicians can handle refrigerant, you may be able to do other repairs, like replacing the compressor, on your own. Alternatively, you may be able to save money by ordering parts for your system and hiring a technician to do the repairs

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