On my Sig with that double ceiling below the AC units I had to unscrew three 7/16 bolts that where sideways above the double center ceiling that could be got at from the drivers side. Actually there were three bolts for the forward ceiling and two bolts for the bedroom ceiling. Once these bolts are removed the double center ceiling swings down on hinges that are on the curb side. Get something to stand up on so you can see above the double ceiling and look at the gap from the drivers side and you will see what I am talking about.
On the front unit I undid the front and back bolts first so it was just held in place with the center bolt then with my wife there to help I undid the last bolt while carefully holding it so it would swing down too fast. To put it back up my wife and I had to swing in back up then I put a phillips screwdriver in the center bolt hole to hold it in place while I screwed the other two bolts in then did the center one.
I used a 1/4 drive ratchet with a long extension.
Once you get the ceilings down the filters are held in place by screws. It is a real dumb design.
If you have more questions you can either email me direct at
mike.c@mindspring.com or ask them on this forum.