central A/C filter question

yes, unless you have some weird A/C unit.

It isn't necessarily the only one. When you have it serviced next, ask the tech to check the air handler or furnace for a factory installed filter, and to check for an electronic filter in the duct system. Normally we wouldn't do this unless we find there's an airflow restriction. I've found second and even third filters on systems that the customer was completely unaware of, so yes, it is possible that you have another, but it isn't necessarily likely. Just the same, if you're concerned about it, have the tech take a peek for you. HTH.

hvacrmedic