Why is my central AC running but not blowing air? Maintenance experts weigh in

There is very little as infuriating as being hot and the AC not working how you want it to. More so when the central AC seems to be running, but no cold air is coming out.  

If you have already tried cleaning your air conditioner, fiddling with the controls, or even banging it on the side in the hopes of spurring it to life and achieving nothing, then it may be a more serious technical issue.

Here, maintenance experts have revealed the five main reasons why your central AC is running but not blowing air so you can rectify the issue and keep your home cool in a heat wave. 

Why an AC is running but not blowing air 

While there are multiple reasons why your air conditioning is running but not blowing air, these are the five most common causes according to experts – and some are more serious than others.  

1. The internal mechanics have failed

If your central air conditioning unit is turning on, but no air is leaving the system at all, it could be that one or more of several internal components have failed, suggests Anthony Fenn, licensed air conditioning contractor and owner of Assured Air Conditioning and Simple Social. A range of technical issues could have taken place:

‘Indoor air circulation issues can be caused by failed indoor fan motors, failed capacitors (a capacitor is almost like a battery that helps the motor start), or a failed module (newer motors use a computer module that is attached directly to the motor for speed control and is susceptible to power surges, with summer thunderstorms causing many module failures),’ he explains. 

These problems are more likely to occur in older air conditioning units, if you have had severe weather, and are more common in some air conditioning types than others, he adds. If you have been able to rule all other possible causes out, then it could be a failure causing your cooling system issues.

Anthony Fenn

Anthony Fenn has over one decade in the HVAC industry as a certified class A air conditioner contractor in Florida. He now runs Simple Social, a platform to help contractors find work and increase the reach of their client base.

2. The air filter or vents are clogged or dirty

Surface cleaning your air conditioner may not be enough to deep clean vents and filters, leading to reduced airflow, continues Taras Stomin, the air duct cleaning expert at Home Alliance. You should examine the air filter and clean or replace it if necessary, ideally every one to three months depending on your usage and air quality, they suggest. An inexpensive air conditioner fin cleaner kit, at Amazon, will make life easier.

It may also be that the vents are blocked completely by furniture or other home decors, Taras adds. This impedes airflow and prevents cool air from circulating properly. Make sure no obstructions are present and clean accordingly, being careful how you vacuum an air conditioner to prevent further damage.

3. The thermostat is not set correctly, or is malfunctioning

If your air conditioner is not blowing cold air but is still circulating some air, it may be that the fault lies in your thermostat, Ben Green, CEO and AC expert at Green Leaf Air points out.

After checking that your thermostat is set to your desired temperature and has not accidentally been adjusted, you should verify that the fan setting is set to auto or on, as the off position would prevent the unit from blowing air, he reminds.

If this has not worked, then it may be that the thermostat is not connecting to your unit as it should, adds Rick Sun, HVAC handyman at Green Leaf Air. ‘This could be caused by a malfunctioning sensor or wiring problem, but only a professional would be able to determine this.’ 

4. The refrigeration cycle is disrupted, and air is not cold

Another reason why your central air conditioner is not blowing cold air is that the refrigeration cycle has been disrupted. This can occur when electrical components fail, the machine is running low on refrigerant, the coils are frozen over, or the components are dirty, says Anthony Fenn, licensed air conditioning contractor. 

These issues are hard to diagnose yourself, so it is worth turning off the machine and calling in a service repair worker to take a look at the internal mechanisms and repair them as necessary.

5. The outside unit is damaged

It can be tempting to think that the issue lies inside your home where the air is not circulating, but it could be the external unit that has sustained damage, or general wear and tear, adds Taras Stomin, air duct cleaning account manager.

‘Check the outdoor unit (condenser) for any visible signs of damage, such as bent or obstructed fins, debris buildup, or ice accumulation,’ they recommend. ‘Clean the unit and remove any debris that may be blocking airflow. Additionally, ensure that the unit's fan is spinning smoothly.’

How to fix a malfunctioning air conditioner

Unlike other home DIY projects, fixing a central AC that is running but not blowing air is not an easy task to embark on your own, especially when the issue is mechanical, says Anthony Fenn, licensed air conditioning contractor 

‘Unless the issue is as simple as needing to clean or replace the filter, or reset the thermostat, the best way to fix issues once they have occurred is to call a professional,’ he says.

‘HVAC systems are very dangerous pieces of equipment and unqualified technicians can easily suffer severe injuries including electrocution, burns, or other serious injuries. HVAC systems are also very expensive and can easily be damaged by improper repairs, and the cost to repair a system that has been tampered with is usually going to exceed that of one that hasn't been touched.

‘A technician can tell if there is a problem before a failure by checking things like refrigerant pressures, motor amperage, and capacitor charge. The best companies will provide you with a written report so that you can compare the values and specifications of your system every six months to recognize trends and potential problems.’

FAQs

It is important to avoid fiddling with electronics that you don't fully understand, even if turned off at the breaker, to prevent causing further damage or injury to yourself and others. 

If you are having issues getting your air conditioner system to blow cool air, then it may be worth picking up some other quick tips to cool down a room without your central AC while waiting on a repair technician.