I can't get under my coach enough to quite make out the label on the air solenoid (eyes too old), and in storage it's dumped all the way down so I can't get my head under the apron. My attempts at research for you went nowhere without the label info.
That said, perhaps the attached will be useful in your understanding of its operation. The air supply is continuous to the black valve part that has the adjusting knob. It shouldn't go over 5 psi or you jeopardize the air bag around the door frame. One caution to new owners, you should try not to open or close the door if the engine is running and in gear; perhaps that seems common sense as it is, but I've seen copilots try to do that underway when realizing the door isn't quite shut. Or they exit suddenly having forgotten something, and the driver (forgetfully and foolishly) had his foot on the brake but was in gear. The inflated air bladder regularly gets torn that way.
The air supply goes through the black regulator first, and only moves on to the bladder around the door frame when the brass solenoid opens when it's activated by 12v. power via the wires you see emanating from it. That power comes from a relay controlled by the neutral safety switch of the tranny and the engine crank relay. That's why I asked if you were certain power was supplied to the solenoid in the first place, and that a relay wasn't the issue; but I assume the tech knew what he was doing, and likely applied an alternate 12v source to test it or bypassed relays in the electrical bay. I'd shop around first before shelling out for the entire unit, just in case the solenoid alone was available. NW RV Supply is a good start, as Gerald suggests. But if you can get more info off the solenoid's label, do some searching for it online.
-Joel
(click on the paper clip icon underneath the image to open a more readable format)