I have a carrier 58stx090 furnace and cannot find anyplace to access to locate/change the filters. The manual says there's one of 2 doors on it but not so in this case.
The air return intake has a filter over it just on the inside of the grate. Could that be the only one? It is a loose piece without frame and just seems to be laid in over the intake.
Home is new and heater seems to be working fine. Any suggestions?

oops= that title should read Carrier Filter... sorry.

Yes that could be the only filter. New home with a junk install. I would call the builder and tell them to fix the air filter situation.