Why Is My AC Not Blowing Cold Air?

HVAC Logo IconBy Tom MoorOctober 3, 2023
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A blast of cold air after a long day in the hot sun is refreshing. But if it's just as warm and humid inside your home as outside it, there's an issue with your cooling system.

An AC not blowing cold air can lead to severe comfort issues and even safety concerns for you, your family, and your pets when the mercury approaches triple digits. Partnering with a reputable HVAC company can help ensure cooling issues like these are taken care of promptly and professionally.

Keep reading to learn more about the most common causes of a house AC not cooling and how to fix them.

Common Causes of an Air Conditioner Not Blowing Cold Air

While many air conditioning problems require the expertise of a certified heating and cooling technician, some can be resolved through DIY methods. We'll discuss both in this section.

Incorrectly Set Thermostat

The first step to take for an air conditioning system not blowing cold air is inspecting whether the thermostat is set correctly. The thermostat is the “brain” of your HVAC system and controls when it turns on and off. In the summer, set the thermostat to “cool.” If it's off, set to “heat,” or on “fan” mode only, switch it back to cooling. If cool air blows from the registers after the system kicks back on, you've solved the problem!

However, if your thermostat is malfunctioning, a professional may need to repair or replace it.

Dirty or Clogged Air Filter

If the thermostat isn't the culprit, move on to the HVAC air filter. Many homeowners don't realize the importance their system's air filter plays in improving indoor air quality and keeping harmful contaminants out of their heating and cooling system. Air filters catch contaminants such as dirt, dust, pet dander, allergens, and mold spores from reentering the air supply.

Clogged air filters restrict airflow which reduces your system's cooling power. In extreme cases, it can cause the air conditioning system to completely shut down to avoid overheating.

The Air Conditioner's Condenser Is Blocked

The last DIY tip to perform before calling an HVAC company is inspecting the condition of the air conditioner's condenser unit, which is the outside portion of a cooling system. Along with a compressor, a fan, and other controls, the AC condenser unit contains the outdoor coil, which is responsible for sending heat from the refrigerant to the outside air. Over time, dirt, grass, twigs, and other debris can accumulate inside the unit and clog the coil, potentially causing your unit to struggle to cool your home or completely break down. You can attempt to clean the coil using DIY methods, but it's recommended to call a professional to prevent damage.

Refrigerant Leak

The air conditioner's refrigerant plays a crucial role in the cooling process, as it pulls warm air from indoors and releases it outside through the compressor. A low refrigerant level due to a leak will cause you air conditioner to inadequately cool your home or fail to cool it at all. Contact a heating and cooling technician if you suspect a refrigerant leak. Refrigerants are dangerous to handle and should only be addressed by a qualified heating and cooling technician.

Damaged AC Blower Fan or Motor

The blower fan is tasked with pushing conditioned air from the air conditioning system through the ductwork, out the vents, and into a home's living areas. If the AC's blower fan or motor is damaged, you may notice weak airflow.

Air Duct Issues

Is your AC running but not cooling? If so, you air ducts could be the reason. Over time, air ducts can develop leaks or blockages that lead to reduced airflow, making it feel like your air conditioner isn't blowing cold air.

Frozen Evaporator Coil

A frozen evaporator coil often causes AC systems to blow inefficient air or shut down completely. The indoor evaporator coil cools the refrigerant and pulls humidity from the air. Frozen evaporator coils are most commonly caused by insufficient airflow because of a clogged air filter, low fan speed, dirty evaporator coil, or clogged condensate drain line. The evaporator coil is difficult to access and can be damaged using DIY methods. Consider calling a professional if your HVAC evaporator coil is frozen.

Improperly Sized AC Unit

An improperly sized air conditioner, both too big or too small, can affect cooing performance. An air conditioner that is too small for the space won't cool it effectively, while an oversized unit can lead to issues such as short cycling. Work with a certified HVAC technician to find the appropriate size system for your home.

How to Prevent AC from Not Cooling

To keep your air conditioner humming along on even the hottest days of the year and avoid inefficient cooling or system breakdowns, it needs regular AC maintenance. Some common ways to avoid an AC not blowing cold air include:

  • Regular tune-ups. Just as your vehicle requires regular oil changes to run properly, your air conditioner also needs regular maintenance to operate at its most efficient and avoid problems such as inefficient or no cooling. A professional HVAC technician should perform an AC tune-up once a year before the cooling season. During a maintenance visit, the technician will inspect, clean, and calibrate all necessary components. They will also inspect for minor AC problems and recommend the needed repairs.
  • Change air filters. Your system's air filter should be changed or cleaned regularly, typically every 2-3 months or according to the manufacturer's guidelines. A clogged air filter restricts airflow which can cause a frozen evaporator coil that leads to poor airflow or a system breakdown.
  • Clean debris around the outdoor condenser. The AC unit needs at least two feet of space around it for optimal performance. Clean any debris, sticks, or leaves away from the unit.

Buying the Appropriate Size Air Conditioner

Size matters when buying a central air conditioning system. Undersized systems struggle to properly cool homes and stay on for extended periods of time, leading to high energy bills and increased wear and tear. Meanwhile, oversized units turn on and off too quickly (short cycling) without adequately cooling or dehumidifying the home.

Unfortunately, the only fix for an undersized or oversized unit is buying an air conditioner that's the appropriate size for your space. Cooling capacity is determined by British Thermal Units, or tons. For example, a 3,000-square-foot home typically requires 60,000 BTUh to adequately cool the space, although several other factors play a role.

Before buying an air conditioner, a qualified HVAC technician should perform a Manual J calculation of your home to determine the exact size air conditioner to install. Aside from square footage, a Manual J calculator also factors in the number of doors and windows, the ceiling height, the climate zone you live in, insulation levels, your family size, sun exposure, and more.

FAQs on AC Not Blowing Cold Air

Why is my AC not blowing cold air but running?

Several issues can lead to an AC not blowing cold air but not running. Some of the most common include refrigerant leaks, clogged air filters, thermostat issues, or frozen AC evaporator coils.

How do I fix my AC not getting cold?

Determining how to fix an AC that's not getting cold depends on the problem. First, check if the thermostat is set to “cool” and whether the air filter is clogged. If neither is the problem, contact an HVAC technician who can inspect for a refrigerant leak, frozen evaporator coil, or other AC issues.

Why is my AC not cooling below 75?

Is your AC not cooling enough? An AC not cooling below 75 degrees is frequently caused by a clogged air filter that is restricting airflow. Replace or clean your HVAC air filters on a regular basis.

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