What happens if you run an AC without a filter

Published On: July 17, 20200 Comments on What happens if you run an AC without a filterTags: , Last Updated: February 11, 20244.9 min read

So you’ve decided to perform a visual inspection of your filter and found out that it’s dirty and clogged. Now, to keep all that dirt & dust from recirculating in your home, you may have removed the filter before getting a replacement. Alternatively, you may feel that your air conditioning system is struggling to cool your home effectively. You heard from someone that removing the filter may improve the AC performance. Right?

What happens if you run an AC without a filter

Having no filter in the AC unit invites a range of problems. Your AC will not run better without a filter, but it might even break down.

Why filters are integral parts of an AC

Having clean air circulating through your home is not only important to your health, but it’s also critical for the performance of the AC system. The system functions like one big loop – everything is connected. Part of the air expelled from the AC  is sucked into the equipment again where it’s conditioned and redistributed. Without a filter, dust particles remain suspended in the air because there is no chance to settle down. The range of particulates and contaminants to be worried about is broad:  Pollen,  bacterias microfibers, mold spores, wood particles, fur from pets, etc.

8 key problems of running AC without a filter

  1. The AC system becomes dirtier:  As the air recirculates inside the system,  the particulates and contaminants will settle down along parts of the equipment resulting in build-ups. Critical areas that get dirty are the blower motor and evaporator coils.
  2. Reduction in the cooling capacity: Your evaporator coils carry the refrigerant that absorbs heat from the air. Your evaporator coils have to be kept clean since dirty coils limit heat transfer. Without a filter, it’s much easier for a fine layer of dust to settle on the evaporator coils and fins.
  3. More energy use:  If your system cannot cool the air faster, it means that it has to be operated for a longer time. You will have to spend more on energy costs.
  4. Your AC may break down:  The refrigerant has to be cold before it flows through the evaporator coils. In the coils, it warms up as it absorbs heat from the air.  If this does not happen properly, the refrigerant will remain cold and may cause the coil to frost over. You may need a very expensive AC repair service down the line.
  5. Growth of mold: Your ductwork is especially susceptible to mold. And if you have no filter in the AC unit, it certainly encourages mold growth. All that is needed is a warm and humid environment. Particulates such as small soil particles that are trapped in your ductwork will absorb moisture. Eventually, your family may be exposed to airborne toxic mold spores that impair health by causing nasal stuffiness, throat irritation, wheezing, etc.
  6. Problems in the condensate drain: As the evaporator coils cool down the air,  there’s the formation of condensate (water droplets). If a lot of dust particles have been washed up by the condensate, they may eventually clog up your drain. If your AC doesn’t drain properly, it may cause flooding and eventually damage electrical parts and even cause short-circuiting.
  7. Development of pinholes in your evaporator coils and leaking of refrigerant: Good filters are also effective in removing volatile organic compounds from the air. These may be produced by air fresheners, certain cleaning chemicals, upholstery, etc.  If VOCs settle on your evaporator coils, they may cause corrosion creating small holes where the refrigerant may begin leaking. Are you facing any problem with your AC? Click here to find out more about air conditioners repair and installation in Phoenix, Arizona.
  8. Breathing in dirty air:  If there is no filter at all,  you can expect to breathe in more particulates, causing a reduction of your indoor air quality. It’s not ideal to have a buildup of pollutants, especially if you have any particular allergies.




Can I run my AC without a filter for one night?

It’s totally understandable that you cannot get a replacement today until the stores are open tomorrow. Or you may be very busy with a particular task. Running AC without a filter for one night should not make a big difference. Now, this advice does not take into account if you live in a very dusty house with lots of pets or dust from outside. In this case, you may choose to turn off the AC at night so you can take advantage of any nighttime air that may cool down the indoor temperatures. If it’s hot outside, prepare for a long night filled with lots of sweating.

What happens if you run an AC without a filter - ACs

Running AC without filter for a day

Running your AC without a filter for one day is the farthest you can go. You may run your AC for one day this way and just get used to it. Remember that dust will keep building up and getting stirred. That’s why your filter eventually gets dirty because there’s always more dust coming in. Soon you may be dealing with itchy or watery eyes, nose, and throat irritation flu-like symptoms, etc. If you’d like to avoid them, have your filter replaced as soon as possible.

Final Word!

Do you dread purchasing a new filter after a few months?  You can choose washable filters instead.  Many companies are now producing washable filters with high MERV ratings. They remain effective even after multiple washes and are built for long-term use. You can even use them to remove most of the microscopic particles from the air. If you live in a high-rise residential property where the air is very clean, and there is less dust in the air, you should also consider replacing your filters on time even to avoid trouble with the management.


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