The cabin air filter, also known as the pollen filter or microfilter, is responsible for filtering the air that the passengers breathe in Subaru Legacy. What happens when this filter becomes too dirty?
Dirty cabin air filter causes the overall ventilation of the interior to deteriorate resulting in reduced cooling and poor airflow in Subaru Legacy. It also puts unnecessary strain on the entire AC system which negatively impacts the fuel consumption.
When the blower motor in Legacy sucks air from the interior or fresh air from the outside (depending on your setting), it first goes through the cabin air filter. This not only protects the blower motor, evaporator, and the heater core from dust and debris, but also improves the quality of air in the interior of the vehicle. When the cabin air filter gets dirty, the blower motor will struggle to push large amount of air though the system and the airflow from the AC vents is reduced.
If the air conditioning system in Legacy is not blowing hard enough or has weak airflow due to clogged cabin air filter, it negatively affects the cooling performance as less air gets pushed through the evaporator coil. This also increase the fuel consumption of the vehicle as the AC system has to work much harder to maintain the desired cabin temperature.
If the AC in your Subaru Legacy smells like a pile of dirty socks, it could be due to unwanted bacteria growth like mold or mildew on the cabin air filter. Inhaling these unpleasant musty odors is not only irritating, breathing the airborne microscopic mold spores can cause allergic reactions in sensitive individuals; such as sneezing, runny nose, red eyes, nausea, and skin rash.
Dirty AC filter is one of the leading causes of bad smell coming from air vents in Legacy. If the cabin air filter has not been replaced for a long time, it can get clogged and harbor mold growth, especially in humid environment.
When to replace the cabin air filter?
There is no fixed time for replacing the cabin air filter, but most manufacturers recommend a change after 10,000-20,000 miles. If you drive your vehicle in dusty or polluted environment, the filter can get dirty much sooner than manufacturer’s recommendation. Additionally, if you drive your Legacy with AC system set to fresh outside air most of the time, your cabin air filter will get dirty much sooner as compared to air recirculation mode.
Replace the filter at the start of every winter for optimal performance
It is generally recommended to replace the cabin air filter every year at the start of the winter season. Spring and summer seasons are hard on the cabin air filter because of pollen and bugs, and in the fall they can get clogged with leaf debris. This gives you a fresh start for the winter, improves defroster performance, and reduces chances of mold or mildew growth.
Can you clean a dirty cabin air filter?
Instead of changing the cabin air filter in Legacy, it is often recommended to first clean the filter. This can be done, for example, with a vacuum cleaner or a compressed air system, removing at least a large part of the visible dirt particles. Unfortunately, this procedure does not allow you to get into the deeper layers of the filter. Therefore, the filter performance will not increase significantly even after cleaning. As a rule, there is no avoiding a change if the filter is dirty.
Dirty evaporator can cause dirty cabin air filter symptoms
Dirty evaporator can also significantly reduce AC airflow and cooling performance in Legacy, which can sometimes be mistaken for clogged cabin air filter. The cabin air filter captures most of the dirt or other airborne particles, but some particles escape and can get lodged on to the evaporator. Over time, these particles build up on the fins and block the airflow through the evaporator coil, causing poor airflow from AC vents and degraded cooling performance.
If you have replaced the cabin air filter, but the airflow and cooling still hasn’t improved, it could be due to excessive dirt and grime on the evaporator.
Symptoms of a dirty evaporator
The two most prominent symptoms of a clogged up evaporator in Legacy are: the air flow from the AC vents is choppy and not smooth, and the inside of the vehicle is developing a bad moldy smell.
Clean the evaporator
Cleaning the evaporator in Legacy is not a simple task. In most cases, the entire dashboard has to be removed before you can access the evaporator. Therefore, it is recommended to do this in a workshop.
Whenever there is a problem with the airflow from the vents, AC cooling, or if there is musty smell, you should always start by inspecting the cabin air filter. You don’t necessarily have to visit a workshop to inspect or replace the filter, as it usually requires following just a few simple steps.