Filters are a very important part of your air conditioning system and is something that needs to be changed on a regular basis. In fact dirty filters can cause premature equipment failer, high electric bills, dusty houses and expensive service calls that could have been avoided by changing them every 30 days. I suggest you use your electric bill as a reminder, every time your bill comes in change your filters ( dirty filters can cause a high electric bill).
There are several differant typres of filters out there to buy, dont be too cheap but you dont need to buy the expensive ones either. I suggest getting a pleated filter but do not follow the suggested replacement time period on the filter. Most pleated filters say they are good for 90 days, but brand new out of the package they are all ready restrictive, then you throw on 90 days worth of dust and animal fur you stand the chance of restricting the air flow to much. So what I do for my own house is I buy the cheap pleated filters (lowes has a 3 pack for $ 7.96 and I believe they are called Natural Aire) and I change them every 30 days and it doesn’t break the bank. Follow this simple step and watch your electric bill go down, your dusting will be easier, and most importantly you system will thank you with many years of cool air.