We had Atwoods on our 2006 Phaeton. Nothing but trouble from the get go. Over the years we replaced them all, some more than once at $700 a pop. Two years ago, 2 jacks broke at once while leveling and made the coach buck like a bucking bronco. Long story short, went to BigFoot in White Pigeon, Michigan, and had them replaced with their system. Very happy with that.
Okay, with the Atwood system, as Doug said, the air dumps when you engage the autolevel on the jacks. The engine is on and you are in neutral. . . it doesn't air back up during this time of leveling. It airs back up when you turn it back on and engage the retract.
Not only is the system no longer made and parts are almost non-existent (we tried before spending the $$ on another system), Atwood itself was bought out by Lippert and that's where it died. We found that the Atwood jacks were made to handle much less weight that the Bigfoot system we had put on. WE are very happy with it.
Dale