Some air system info the leveling system is a secondary air circuit which means it is after the safety valves and gets no air until the main air is above 70psi on most units. The rear will air up faster so it will always come up first. The HWH system uses several valves to level the coach they get air from 2 sources one is the leveling air which has a small tank usually and a small compressor the other is the leveling valves that set the ride height when traveling. So in the front you have a valve body which has 6 valves and gets air from 2 sources or 3 if you have 2 height control valves up front. In travel mode the travel valves connect the height valves to the bags. In level mode the travel valves lock out the height control valves and each bag gets air for the leveling system via the raise valve which adds air or the lower valve which lets it out. The rear of the coach will have the same valve body with 6 relay valve unless it has a tag then it could have 8. When you level the travel valves close and lock out the height control valves and the brain box uses the raise and lower valves for each bag to level. In travel mode which by the way only means the travel valves are open the raise and lower valves are locked out and the travel valve opens to let the height control valves set ride height. For the system to work in travel mode you will have power to each travel valve and no power to the other valves. It really is a simple system you have a passage that can get air from either end one end comes from the height control the other from system air each has a relay operated valve. In the middle is a output to the air bag and a relay valve the when opened lets the air out. So if your front wont come up in travel mode you either have no power to the travel valve or a bad valve or a bad height control valve. I hope this helps.