[Newell 381]

Hey guys, we have been trying to prep Newell 497 to sell and I can't seem to get the front suspension to air up normally. When the coach is started, after air pressure is built up, the front bags do not inflate. I can manually inflate them via the HWH system and it will stay aired up for days. What should I be zeroing in on here? Height control valve maybe? Also, not sure if this helps or even matters, but this coach does have the factory independent front suspension. Thanks in advance