I purchased a condo that has a York air handler... There appears to be a 6" panel missing from the access areas on the front of the air handler, there are 2 other larger panels-- one solid with the schematics on the back and another vented panel.

I cannot locate a replacement panel for the 6" area... and I cannot determine what size or WHERE an air filter would go as the previous owner had none in place.

Thanks for ANY help

Would help to know the position of how the furnace is set up, is it upright/or horrizontal? Is it upflow or down flow? Since I has 2 larger panels I`m guessing it is a gas furnace
Lets work backward from the order of your questions
1st,if you can locate the blower motor housing,it should be on the end where the ductwork return connects to the furnace,you probably see a big hole that needs to be covered by a filter big enough to completely cover the hole, the larger panel that's solid and has the schematics will go on the end where the blower is located (probably won`t fit any other way), so that leaves the vented panel for the other end,probably where the burners are located,now as for the small 6" panel this is a guess,do you see a metal box inside with a bunch of wires in it,,could be a cover of some kind for controls box,,,,,,,maybe the name brand and model number would help to identify the 6" panel
Pictures would help if possible
I`m wondering why past owner had all the panels off and didn` re-install, guessing something might not be working
Please let us know about your success and if we can help farther please ask away

Some older furnaces have open areas ofr intake air and it may appear it needs a panel but does not.

Can you provide us with a picture?
The filter might be inside the unit once you remove the panels.