Why is My Central AC Running but Not Blowing Air?

Coming home or waking up to a central AC that’s not working is no fun. Besides the discomfort, it may pose health risks to your entire family, pets included.

Several reasons can cause your central AC to stop circulating cold air.

It could be low or leaking refrigerant, condenser or evaporator coil problems, clogged or dirty filters and registers, or thermostat issues.

Some of these issues are simple, while others are complex.

But before calling in an HVAC technician, you can troubleshoot the problem yourself and see whether your AC blows air once again.

Read on to learn the leading causes of AC running but not cooling and potential fixes to instantly take care of the issue and get your system working again correctly.

5 Ways to Diagnose Central AC Running but Not Blowing Air

1. Clogged Registers

A clogged air register or vent can restrict air flow, stopping the AC from blowing air.

The return air register takes air into the system and supplies the vents that blow conditioned air into your home.

Your ventilation system runs throughout your house. So, if a leak or blockage occurs in the ductwork, it affects the blowing of air, and by extension, the cooling.

If this air restriction occurs near a vent, the room where the particular vent is is the only one that will feel warmer.

The rest of your house will be cold.

This should indicate a potential ventilation problem in ducts supplying conditioned air around your apartment.

Note that the vent can get closed accidentally.

Especially when only one room is warm, check to ensure the supply vent has no blockage. If you notice any, unclog the register or vent.

2. Clogged or Dirty Air Filter

Every ounce of air output from your air conditioner must pass through the air filters.

Your filters will catch dust, pollen, dirt, or debris in the air. Therefore, it’s recommended to check it regularly because clogging can result in airflow restriction.

A dirty air filter is one of the most common causes of your AC running but not blowing air.

The bad news is that once the clogging restricts airflow, other parts of the AC, such as the fan, compressor, and motor, start overcompensating to generate more airflow.

This must happen for the system to satisfy your thermostat’s temperature setting.

In short, clogged air filters can result in serious problems. It might sound like something small, but it causes other parts of your AC to wear out faster. 

Fortunately, most air conditioners feature an in-built switch that shuts it down once the filters get too clogged. 

If you identify a clogged filter as the problem, clean it thoroughly to remove the accumulated dirt.

If it has been there long enough, the best course of action is a replacement.

Experts recommend replacing your air filter every three months. If you have pets in your home, make it even more often.

It’s worth noting that clogged air filters might shut the compressor off before the fan. The result is your air conditioner running normally but not blowing cold air. 

Replacing an air filter yourself is easy. However, if you’re unsure about how to go about it or which filter to use, it’s best to seek help from an AC technician.

3. Problems with the Condenser or Evaporator Coil

While air filters do their best to keep the air and coils clean and performing optimally, evaporator coils wear out over time.

The result is problems such as mold and mildew growth. This is due to the constant moisture causing condensation or ice build-up

Low refrigerant in your AC can also cause the evaporator coils to freeze up. The result is your AC will run without blowing air.

Although uncommon, the condenser is also prone to wear and tear over time.

Therefore, if you cannot identify any other issue with your air conditioner that’s preventing it from blowing air, check your condenser.

Having UV lights comes in handy as it guards against mold and mildew growth and keeps your air clean.

If you observe a frozen-up coil, turn your AC off and melt the ice.

Turning on the only fan on your air conditioner should do it. Alternatively, you can use a hairdryer to fasten the process.

Don’t hesitate to call in an HVAC professional when you identify issues with condensers and coils because they can result in significant disruption within your AC unit.

After removing the ice buildup, you can resume using the AC.

4. Clogged Drain

Did you know that all air conditioners work as dehumidifiers?

Bigger AC units (3+ tons) can remove up to 100 pints or more moisture from your indoor air. This water has to find its way out. This is where drainage systems come in.

A drainage pipe or hose drains the collected water out. So, if the drain clogs, your AC unit will accumulate some water. What you’ll have is a flooded air conditioner.

This may lead to the compressor shutting down.

This compressor is the AC part responsible for achieving that cooling effect in the AC unit cooling coils.

Surprisingly, the fan might work as usual, but the AC will run without cooling your home.

Fortunately, clogging a blocked AC drain is easy.

Check the location of your AC unit, and if you notice any mold, debris, algae, leaves, or hair in the piping, flush it out.

Household cleaning agents can get the job done, leaving the drain clean. This can also help remove smells coming from your AC.

Sometimes, the dirt might be too much, so cleaning the pipe is next to impossible. In this case, it’s better to replace the drain pipe

5. Thermostat Issues

All the action starts at the thermostat. Until the air temperature in your house exceeds the control setting, your AC won’t turn on. 

Common problems with the thermostat include:

  • Inability to set the thermostat to a desirable temperature (below your room temperature).
  • The thermostat depletes or almost empties its batteries.
  • Faulty connection of the thermostat.

All these can result in the AC running but not blowing cold air.

Always ensure you set your thermostat to cool or auto and not heat.

This should be the starting point. Remember, if you accidentally set it to heat, this can cause the problem. 

If changing these settings doesn’t get the AC blowing air, the problem lies with the thermostat specifically.

Near-depletion thermostat batteries don’t have enough energy to communicate to your AC unit. They need replacing.

Sometimes the problem is due to a thermostat wiring mistake, particularly with a newly-wired air conditioner, or wires that are not correctly fixed in thermostat sockets.

The result is your brand-new AC unit not blowing air.

The thermostat setting and almost-depleted batteries are easy to fix. As for wiring issues, you need to call an AC technician if you’re unsure how to do it. 

When to Call an HVAC Technician

1. Low or Leaking Refrigerant

The refrigerant in your unit might run low, requiring you to top it up. The most likely cause is a refrigerant leak. 

A refrigerant leak is an issue that only an HVAC professional should address. Therefore, don’t try to handle the chemical yourself—it can be dangerous.

2. Damaged Air Ducts

If you observe no air blowing out of your registers, the problem might be with the ductwork. They can get damaged or clogged over time, restricting proper airflow.

Call in an AC technician who’ll inspect your ductwork and clean it. This will ensure air keeps moving from your air conditioner throughout your home uninterrupted.

3. Electrical Issues

Electricity issues that may cause the AC unit to run but not blow air include:

  • Incorrect plugging of the power cable into the outlet
  • Damaged power cables
  • Blown up fuses
  • Tripping amp breakers

It goes without saying that electrical issues are not for everyone to deal with.

If you notice the AC unit has cold air blowing but stops abruptly, check if the amp breaker has tripped or the fuse blown and call in an AC expert right away.

Final Thoughts

During summer, there’s no doubt you need your AC unit in tip-top shape and running all through.

If the opposite happens and your air conditioner runs but doesn’t blow cold air, your whole house will be in a mess.

Fortunately, you now understand the possible causes of this problem. Better, you know how to fix them. Some are easy to solve, while others are pretty extensive.

If you’re not sure what’s causing your AC unit to run but not blow air, you owe it to your family to call an HVAC technician who will assess the situation and fix the issue. 

It’s important to distinguish if your AC is blowing hot air as well, because that’s a different problem in itself.

About Roy Cohen

Roy Cohen has a burning passion for heating, cooling, and ventilation. He aims to help you save money on expensive repairs and bring you the best HVAC products. He has years of experience behind him in HVAC repair and garage maintenance.

You can find Roy at his LinkedIn or his email: [email protected]

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