dusty condo, where is the filter?

Depends.

Many condos have individual air handlers under each window where hot or cold (depending on season) water is pumped through from a central plant. The cover comes off and a foam time filter can been seen and either replaced or washed. While you are there you might want to oil the fan motor.

Other condos have house type air handlers or furnaces. Just change the filter.

It may be almost anywhere. I suggest asking a neighbor.

Note: changing the filter may not help you reduce the dust in your condo, but it should go a long way towards protecting the heating - cooling system from that dust.

You might try cleaning!

Note this is just lamer that has nothing better to do then ask dumb questions! Using many nicknames.