OldGerman.....If your 05 is like mine, you should have a louvered door just in front of the left rear tire. It will take a round barrel key to open. Open the door and there should be another lock that opens the cooling unit which is part of your dash A/C. Behind that you'll see a large pump on the open floor of the compartment. There should also be two fuel filters and the other large filter is your air dryer filter.
The large pump, valves and tank will have three "T" handle knobs on the top. Make sure all of them are snug, (hand tighten).
Don & Mary
2019 Newmar Dutch Star 4018
2019 Ford Raptor