On Mon, 12 May 2008 07:05:00 -0700 (PDT),
wrote:

Hi,
I've been in my house for a year, I looked inside all of the interior
air intakes for my central air system, and none of them seem to have a
filter. I was in the crawl space yesterday and saw what look like used
filters, left by prefvious owner. Do all Central air systems have
filters? If the filters is not in the intakes where are they? The
machinery of central air system is in the crawl space, is the filter
located in this part of the system?

Yep, that's generally where the filter is located. It will be where
the intake air goes into the unit.