I am trying to figure out why my air filter in the dining room has turned black on the intake which is in the ceiling. What would cause that to happen. We have electric central air and heat.. Hope someone can help me figure this out cause I sure don't have the money to pay for a big repair.
Thanks,
Tina

It is called dirt or it could be mold. With the return at the ceiling you are scrubbing all the nastys and the filter does a better job than one at floor level. Naturally the best place to have a return air depends upon weather you are in the heat mode or the cooling mode.