Filter location cannot locate where filter is located to change it

Is this a split system or package unit. if u don't have a filtered return inside the house where the return air is and just grilles( return is the air being sucked back to furnace). look inside the furnace where the blower motor is the filters can be in the plenum above the blower if its a counter flow or if its upflow they might be below the the blower or on the side of the blower. wherever the return air comes back to the furnace look there. also if there is 2 panels behind the flue pipe that may go up remove the right side panel and there may be 2 filters in a v pattern above the blower.