Just thought I'd post this here for anyone with the same issue in the future.
When preparing to return home from our destination I noticed that the drivers side of the Motorhome was really low on ride height - so low I wouldn't have been able to steer due to the tire rubbing in the wheel well. All 3 other air bags aired up fine.
Upon closer inspection I noticed one of the leveling linkage rubber bushings was broken near the top, see attached picture. These leveling links attach to the ride height control valve at one end and to the bottom of the axle at the other end. As the coach rolls back and forth while driving or if you're loaded unequally these arms push/pull the height control valve to either increase or release pressure in an attempt to level the coach. If the leveling linkage is broken the ride height control valve stays neutral which means no air in or out at all.
I used a small bungee cord to re-attach the two halves back together just so I could get it home. The next day I was able to get the Haldex universal replacement universal linkages from a local truck supply company PTS
- total cost $12.00 each! On my chassis there are 3, one on each front air bag and one in the center of the rear axle controlling both air bags (yours may be different). EASY to change, took all of 30 minutes to do. I measured the length of the original ones and cut the new ones the same.
So if your chassis has some age like ours does, I'd suggest looking into replacing these before they break or split - you cannot drive it at all if the air bag doesn't air up - likewise I wouldn't want to be driving along and have one break either.