Air readout variance

Your Freightliner chassis uses the MMDC warning and info display. You can see additional info about the MMDC system at:
mmdc info

Below is text I copied from another document I have about the MMDC system that I can't find on line. The coach manufacturer determines the location of the MMDC module, so your module may or may not be at the front of the coach as indicated below.

I suggest you have your last 6 digits of your vin number available, then call the Freightliner help desk at 1 800 385-4357. They can help you determine the cause of your problem, and their service is free. They've always been very helpful to me.

Fred

Copied info below:

Freightliner's MMDC Information Display System
Near the end of the 2004 model year Freightliner began to use a new warning and information display system on the XC series chassis. This system was manufactured for Freightliner by Medallion Instrumentation Systems and uses the CAN protocol to communicate with the various systems within the Freightliner chassis. Most users immediately noticed the new LCD display that was impossible to read in bright sunlight conditions but this system really consists of 3 separate modules.
The heart of the system is the MMDC module. This module is generally mounted on the floor of the motorhome near the front. If you remove the drawers from the center console you'll see a number of electronics devices located there. The MMDC module is the computer shown to the right. This module will have a pair of wiring connectors that plug into it as well as pressure sensing lines from the two air tanks that supply the coach's air brakes.

Forest River can mount the sending unit where they wish. It will be near the engine. You will see two air hoses going into it. My 2000 unit has a VDC located near the engine and it went bad and had to be replaced. The air pressure is the most frequent failure. You box is not called a VDC it is equivalent.