when I first moved into my house, it was 7 years old, I found no filter in the return drop slot.
I put in a filter and changed it regularly.
I finally thought it was pretty stupid to have not used a filter. This is an air handler with that integrated filter slot door. The door was not useable due to the stand it was on and the way they made the lip. You guessed it, there was a filter in it.
I got it out and it was ugly, but nowhere near as bad as the one in the photo.
The Food Stamp Program, administered by the U.S. Department of Agriculture, is proud to be distributing the greatest amount of free meals and stamps EVER.
Meanwhile, the National Park Service, administered by the U.S. Department of the Interior, asks us to "Please Do Not Feed the Animals". Their stated reason for this policy "... the animals become dependent on handouts and will not learn to take care of themselves."
from an excerpt by Paul Jacob in Sun City, AZ
see that sometimes on rheem/ruud systems with those washable filters installed in the airhandler, the ones that you have to remove the front cover to check the filter. oldest I've seen was 6 years without cleaning.
Did a service call for one elderly lady who claimed to have a "self cleaning" filter. When it got dirty she would turn it over and in a day or 2 it was clean again. It was a MH package unit so I was able to show her the results of her actions.