Not too usuful for filling tires
I suspected a similar issue when we bought our new Tiffin. For me, when the tank pressure is low, I can insert my standard male fitting on my hose and everything works fine. At full tank pressure, I can't insert the same fitting (maybe I'm just a 98 lb weakling).
On doing some reading, the air suspension pressure is a little low for filling tires. You may need to run the engine to keep the pressure high enough. So I don't use the system.
Brad & Dianna
2017 Allegro Bus 37AP
2015 Jeep Cherokee