A Dirty AC Air Filter Reduces Your AC’s Performance. Change It (DIY)

duct AC air filter
Air filter of a ducted split-unit AC

An Air Conditioner installed with technical precision serves long enough before experiencing any major breakdown. An expert has to service it as per technical recommendation, though. Regular maintenance ensure no premature breakdown that would render your AC inoperable so soon. And one of the regular maintenance is cleaning or changing the AC Air Filter.

Lack of AC air filter cleaning or changing at the right time degenerates to inefficient cooling.

Suppose your AC has been performing well. Suddenly, you notice a glitch like, “No cooling from the indoor unit or duct. Or, the cooling effect is insufficient.” Such anomaly is a sign of underlying fault brought about by using your AC for long without service. It can also mean a component of the AC has broken down.

If you’re the AC owner and have HVAC expertise, it’s easy to diagnose and work on your AC. But if you don’t have the skill, little ambition is enough for you to handle some DIY fixes.

However, if you are less interested in the hands-on aspect of service and maintenance, you can still learn a thing or two about your AC.

Read through this article to enable you to gain general knowledge about AC service and maintenance. It’s resourceful to have a rough idea of the work an AC technician would come to do on your machine.

So let’s look into the fault highlighted in bold Italic above.

No cooling from the indoor unit or duct. Or, the overall cooling effect is insufficient.

split phase AC evaporator
Split-phase AC indoor unit

An Indoor Unit or Evaporator (shown above) is the part of a split-type air conditioner installed in the conditioned room. For an AC with a duct system, the evaporator sits outside the conditioned room. Many designs place the evaporator assembly in the basement. In houses without a basement, technicians mount the evaporator in a convenient spot outside the main conditioned room.

Evaporator fan draws air from the conditioned room via the “return side” of the duct. AC air filter restrains fine dust and particulate pollution contained in the air before the air reaches evaporator coil surface. The fan finally pushes clean low-temperature air through the discharge side of the duct. Nothing but pure air should flow across evaporator fins.

After your AC has run for six months, the filter gathers dust, and the time for maintenance comes. The time can be shorter in a dusty weather.

To understand how important this maintenance is, compare the situation with changing your car’s air filter. What do you think would transpire if you don’t change your car’s air filter according to your vehicle manufacturer’s recommendation?

For your AC, if you don’t clean or change the filter, you’ll experience a negative change in performance. This change can happen before or after your AC reaches its scheduled service time – planning your service time depends on how clean your surrounding air is. Smoggy environment means frequent service and maintenance.

If you experience reduced cooling, first check the AC air filter.

Air Filter

The air filter is an element of AC that restricts foreign particles other than air molecules from reaching evaporator coil. Air filter has tiny pores that allow air molecules through but blocks dust particles. This filtration ensures that air circulated in the conditioned room is clean for respiration.

In a split-phase AC, the air filter is in the indoor unit, and in a duct system AC, it’s within the air handler assembly.

The two main filters are reusable and disposable filters. When you do service to your AC, you clean and use again reusable filters, but throw away disposable filters. The degree of filtration also defines the quality of a filter.

Dust and dirt sieved by the filter form a layer on the filter after weeks of operation. This dust blocks the pores and hinders free air flow. The resultant effect of this phenomenon is “impaired airflow across the filter and evaporator coil.” Eventually, there’ll be no sufficient cool air coming from the indoor unit. Not until you clean the filter.

I want to use a split-phase air conditioner, as an example, to show you the solution.

Before cleaning the filter, switch off the AC from the wall switch, or user interface remote control if your AC has one, then proceed as follows:

  1. Pry out the front evaporator cover and open it as shown in the photo below. A split-phase indoor unit has a pair of filters placed side by side.

    AC air filter in cassette
    Opened indoor unit
  2. Pull out the reusable filter from its cassette. Most indoor unit filters are reusable plastic filters. If the AC has operated for three to six months without cleaning the filter, it’s now full of dust and dirt.
  3. Use a hand blower (if available) to blow off the dust from the filter, then scrub it with a soft brush in soapy water. Put it out in the sun to dry before you insert it back.
  4. As the filter dries out, you’d want to find out if the indoor unit has gathered dust hidden in inaccessible joints – in most cases, there is concealed dust and dirt.
    Use a portable vacuum cleaner (with nozzle) to suck the hidden dust.

    reusable washable AC air filter
    Reusable washable air filter pulled out from the indoor unit


The two procedures for replacing disposable and reusable AC Air Filters have no much difference. For a split-phase indoor unit, it’s as easy as opening the evaporator cover, removing the filter, cleaning, and inserting back; dispose and replace with a new one in the case of a disposable filter.

Some duct systems have their air filters secured in place with screws. Locate the screws, unscrew, and remove the filter. Clean and put back, or replace if it’s a disposable filter.

Ignoring to service (in this case, cleaning the filter) your AC only compounds its problems. One disadvantage is that your electricity bill will go up as your AC struggles to “breathe its last.”

If your AC has a problem that you think is not associated with the filter, let me know in the comment section so that we can discuss its solution.