Air conditioner filters filter out debris, dust, and other allergens from your home's air supply, providing you with clean, cool air. However, over time detritus will build up in your filter, which will increase the load placed on your air conditioner, causing it to operate less efficiently, using more power to produce less cool air. When this happens, you will either need to replace or clean your air filter to keep your air conditioner operating as it should. Thankfully, there are a number of warning signs that you can look out for to determine when it's time to replace your air conditioner's air filter.

Reduced Airflow

If the air flow throughout your house is noticeably reduced, your air filter may be clogged. Check various vents throughout your house. If they all seem to be producing the same amount of air flow, you should check your filter. However, if some vents still provide normal airflow, the issue may actually be with your ducts, not your filter. Check the filter anyway – if it's clean, it's time to clean out your ducts, as dust and other clogs have built up there instead.

Odd Smell

If you notice an odd smell moving throughout your home, but with no noticeable source, it may be because of your air conditioner. Once the air filter becomes clogged, dirt and other debris can get into your duct system, which can cause mold and mildew growth, a serious health hazard. Have your air filter changed or replaced, and clean out your ducts as well.

High Energy Bills

If you notice an increase in your energy bills without a corresponding increase in the amount of usage that you are getting out of your appliances, the culprit may be your air conditioner. A clogged air filter places greater strain on the cooling system, as the system is not getting as much air as it needs, and because dirt may be building up on the fan blades within the air conditioner itself. Check the air filter, and clean off the fan and any other visibly dirty parts of your air conditioner.


If your air conditioner suddenly and inexplicably stops working, it could be because the air filter is completely clogged. This is a warning sign that is hard to miss, but the cause of it can be confusing for homeowners. If your air conditioner no longer operates at all, call an HVAC specialist like Enright and Sons to look at your machine. This will only happen if you do not change your air filter for a significant period of time.