I change muh a/c filter once a month. I have a 3 ton York a/c system. It is good. Muh house is not that big that is why i have a 3 ton. The unit is 2-4 years old. If anyone has pictures of old a/c's please post here. Some times people never change their filter and the coil looks like a animal got sucked up in the return. It is funny.