Your air conditioner provides your living space with refreshing and conditioned air during the hot summer months. However, it can be frustrating to get home from work only to be greeted by hot air instead of a cool breeze. An air conditioner that’s not blowing cool air is a common problem many homeowners experience and can be caused by many factors.

Understanding why your air conditioning unit blows warm air can help you solve the problem and get your system back to running properly. Here are the seven common reasons your cooling unit might be blowing warm air and tips to diagnose and fix the problem.

1. Low or Leaking Refrigerant

Refrigerant is the fluid used in air conditioning units to cool the air circulating through the system. If there is a leakage in the coils or refrigerant lines, the refrigerant level in the cooling unit will decrease, resulting in warm air blowing from your vents or even reduced cooling performance.

Over time, the refrigerant leaks can lead to low refrigerant levels. When your air conditioning system has low refrigerant levels, the unit will overwork to cool your home, leading to higher energy consumption and increased energy bills. Besides, running your air conditioner with low refrigerant can also cause damage to its compressor and other major components of the unit, resulting in expensive repairs.

If you see refrigerant leaks or suspect your unit’s refrigerant levels are low, contact an HVAC technician immediately. These professionals will locate and identify the refrigerant leak. They’ll also recharge your air conditioning unit with the right amount of refrigerant to ensure it’s running properly and more efficiently.

2. A Faulty or Wrongly Calibrated Thermostat

The thermostat controls your home’s temperature and communicates with your AC unit to turn it off and on as needed. If the thermostat is broken or not working correctly, it might not communicate well with your AC unit, resulting in a lack of conditioned air.

A wrongly calibrated thermostat can also cause your cooling unit to blow hot air. First, check your thermostat settings and be sure it’s set to cool. However, if the setting is correct, check the temperature settings to ensure none of your home occupants has changed them. If the registers are still blowing cold air, call your AC technician. The expert will check your thermostat and either repair or replace the thermostat to get your cooling unit working properly again.

3. Dirty Filters

The other reason why your AC system is not blowing cold air is a dirty filter. AC filters trap dirt, dust, and other pollutants circulating in your indoor air. Over time, the filters can get clogged with debris, restricting airflow and reducing the unit’s capacity to cool your living space effectively.

When airflow is restricted, your air conditioner will have to work harder to cool and distribute air which can cause the unit to overheat and trip the safety switches. As a result, the system will blow hot air or shut down. Overworking your cooling unit can also increase the tear and wear of the unit’s components, leading to expensive repairs.


Experts recommend replacing or cleaning every 30 to 90 days, depending on the pollution level in your area and how often you use your air conditioner. Replacing or cleaning your filters regularly can help keep your unit working effectively and efficiently.

4. Clogged or Blocked Registers

Like dirty filters hinder airflow, clogged vents or registers do the same. You can find registers around windows, ceilings, or doors. These units are often made of plastic or metal, and they help distribute the conditioned air to your indoor environment. Return registers take air into the AC unit, and supply vents blow the cooled air into the living space.

When they get blocked, the conditioned air cannot get past them. Potted plants, furniture, or other household items often block the registers. Removing the items away from the registers and cleaning them more often can help prevent airflow problems.

5. A Malfunctioning Compressor

The compressor is a vital part of your cooling system since it compresses and distributes refrigerant in the unit. If the AC compressor is not functioning properly, it affects the whole system. As a result, your air conditioner might lose its cooling capacity, and your vents will produce hot air.

There are many reasons why your AC compressor can malfunction, including the following:
  • Mechanical problems
  • Electrical issues
  • Dirty filter
  • Refrigerant issue
  • Lack of maintenance

If you suspect that your compressor is faulty or broken, it’s important to contact an expert to diagnose and fix the problem. The professional can easily identify the main problem and determine the best action to restore your air conditioning unit.

6. Problems With the Condenser or Evaporator Coil

The condenser and evaporator coil removes heat from the indoor air, blowing conditioned air into your living space. If you notice ice or frost on the outside or inside of these components, it might be important to contact an AC expert.

The condenser is installed outside and can get clogged with debris over time. As a result, your AC compressor will work harder to cool your house, which can lead to ice formations on the coil. Sometimes, the evaporator might freeze due to low refrigerant levels. Low refrigerant causes the compressor to overwork to cool, causing the evaporator coil to freeze.

These two issues are not easy to diagnose. Therefore, it’s important to call your HVAC professional immediately to handle the problem.

7. Your Ducts Are Leaking

When air is cooled in your air conditioner, it passes via a network of insulated ducts. The ductwork has return air ducts and a supply system within floors, ceilings, and walls. If your AC unit produces warm air, there could be a leaking problem with your ducts. Duct leaks can occur due to poor installation and damage to the ducts and can be found anywhere within the duct system.

Leaking ductwork can cause your cooling system to blow warm air since it allows the conditioned air to escape from the unit before it reaches the desired space. It can also allow warm air to enter the AC, reducing its efficiency and forcing it to overwork to cool your indoor environment.

It’s important to have the ducts inspected regularly by an experienced technician to prevent leaking ductwork from causing your air conditioner to produce warm air. These professionals can locate leaks in the air conditioning unit and make the necessary repairs to ensure the system works properly and efficiently.

Partner With the Cooling Experts Today

From simple issues like a wrongly-set thermostat to more complex situations like a damaged processor, there are many reasons why you might find your cooling unit running but blowing hot air. Ignoring this problem can make your living space uncomfortable and even lead to premature failure of the system.

If your AC is not cooling your indoor environment, our technicians at John Henry's Plumbing, Heating, Air, and Electrical can help. Our experienced HVAC experts will inspect your air conditioning unit, diagnose the issue and make repairs to keep your home comfortable throughout the cooling season.

We also offer heating, plumbing, drain, and sewer line services throughout Lincoln, NE, and the surrounding areas. Contact us today for professional air conditioning services, and we’ll gladly serve you.

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