Phone the chassis manufacturer , Freightliner or Spartan ; and get them to e mail you an air system diagram for your coach , anyone trying to service the system will need it . Have your serial number handy.
Freightliner , free help line . 1-800-385-4357
Spartan Motor Home Support . 1-800-543-4277
Was there an air bag replaced ?
The low air pressure , do you have multiple air gauges on your suspension system?