When ice forms on your AC unit, it cannot cool properly. This also puts a lot of strain on your compressor. If you run your unit when there it ice on it, you may end up needing a costly repair, or you may even have to replace your unit. Even new systems can ice up and break down.
You should check your air filters AT LEAST once a month, and during peak season, you should check them more often. You may be surprised at the amount of dirt that collects on them. Also check your intake registers to be sure that there is nothing blocking them. Your air conditioner is a valuable part of your home. This simple maintenance procedure is vital to ensuring that it gives you many years of effective and efficient service.