I've got a 3-year old home with central air. A Janitrol air handler unit in the basement, compressor/fan outside. We've been seeing a lot of dust in the house and thought I should look at the air filter. Unfortunately, I cannot seem to find an air filter anywhere on the unit. It's not down where the return enters the unit. I've taken a number of panels off and looked at the product literature and can't find anything. Is it possible that my entire AC system was installed without a filter? And, if that's the case, what are my options for installing one? I have only two return registers that are easily accessible. It seems I could install filters on them, but am not really sure what type of hardware I would need. Any search I do online for air filters just brings me to someone selling replacement filters. I haven't seem anything showing how to install the filter brackets or holders inside my return registers. Any help greatly appreciated. We've got a newborn in the house, and I'd love to make sure the air is a clean as possible. Thanks!