The air conditioner's filter needs to be changed regularly. You should either wash it off, if it's reusable, or replace the filter at least once every six months. Three months is average, and monthly is ideal if you use it a lot or if your have pets and/or smokers in the house.
What happens if you forget to change the air filter? For one, you'll have more allergens in the house as the AC unit blows dust and dander through the registers. You'll also have a higher cooling bill. You could even end up with the need for a repair. Below are some of the ways a dirty AC filter could lead to you calling for repairs.
The air conditioner filter is located at the air intake valve. Its purpose is to prevent dirt from entering the inside of the AC unit. You can choose from different levels of filters, with some even providing medical-grade protection. But even a basic filter prevents miniscule particles from entering the machinery.
The problem with even miniscule particles is that they can build up over time. If debris gets through your filter regularly because it's already clogged, it will start to build up on the machinery parts. It'll especially stick to parts with lubricant, which will cause an impediment to those moving parts. Your AC can then freeze up. An HVAC technician will have to take it apart and clean the parts.
If the filter becomes clogged enough, the air might not flow efficiently through it. AC units depend on a good flow of air. Without it, not only do they have nothing to cool, but their parts can't operate as designed. The reduction of air flow especially impacts the evaporator coils.
The evaporator coils house the refrigerant. Their purpose is to draw heat out of the air and transfer it to the refrigerant. As experts point out, the coils can develop ice crystals on the outside if there's not enough air flow. You can defrost the coils, but a tech will need to come clean them.
Short cycling is a situation in which the air conditioner cycles on and off quickly. Not only does short cycling lead to ineffective cooling in your home, but it puts a strain on your system. The AC unit might start short cycling if it's not getting that clean air because of a dirty filter.
Manufacturers build AC units to cool for a period of time followed by a period of being idle. If the unit is short cycling, though, its machinery will start to wear out. You'll probably start hearing squeaks and rattles that indicate broken or loose parts in the unit, which will require repair.
Call for AC repair if a dirty filter caused any of the above problems.