Chassis Air Gauge

it is not front and rear gauges.
they are primary and secondary tank readings.
when your system is so called empty of air pull lanyards on tanks most likely one will still be aired

When I bought my MH both tanks needed to fill whenever I started the engine. A few months ago I heard an air leak coming from one of the fittings. I replaced it and now whenever I start the engine even a few weeks later, one tank is still aired up. I think that is what is supposed to happen. I like it!

talotto wrote:
Looking for advice. My "Front Air" gauge reads 100 anytime the motorhome switch is on, whether I've started the engine or not, whether air has built up or not. The rear gauge reads correctly - 0 when air is depleted and 110-125 or so (estimated) when the system is charged and cycling.

So, I'm thinking bad gauge, replaced the gauge. Same problem with the new one. The new one reads 100 PSI when on.

So now I'm thinking pressure sensor or wiring, so to test that I swapped the gauge input plugs (front gauge connected to rear wiring, rear gauge connected to front wiring). SAME SYMPTOM! Front gauge still shows 100PSI when powered - whether air system is charged or not, rear gauge follows the air pressure as normal.

There isn't a separate ground - it's all in the plug, and I swapped the plugs (as noted above).

In all of this the air system works properly, that is, the brakes work (i.e., release when aired, lock tight when not) motorhome drives and rides right, the chassis suspension bags air up, all appears to be correct ride height front and rear, side to side. No air alarm once the rear gauge gets above about 60-65.

So, any ideas? I know I'm missing something, but what?

It's a 2004 ITASCA Meridian, 36G Diesel pusher.

Tony

Tony,
We have the next model up, same year from yours. It's the '04 Itasca Horizon, 36GD with the C-7 330HP CAT. Now, your air gauges, are powered up by what's called the MMDC. Multi-Module-Data-Controller. The air lines enter into that MMDC and, are coupled with what's called a "Transducer". It basically changes a mechanical mechanism to an electronic one and then, sends it to the gauges for you to read.

Now, in our coach, that MMDC is located in the left front lower compartment, with a whole ton of other breakers, relays and more. On your coach, I'm not exactly sure where it's at. It's most likely in the cab and under the dash. Someone will chime in here with it's exact local.

Now, once you find it, here's little test. Bleed the air system down, almost to zero psi and then, to get those hoses, one green, one red, (front - rear) out of the MMDC, you simply push in on a small collar that's right at where they enter the box. That will release the hold on those hoses. If there's any air still in the system, it will escape when they're pulled out.

Now, just for grins and, maybe to check on our notion of a bad gauge, simply re-insert those hoses in the opposite holes. That is, put the rear hose in the front socket and, the front hose, in the rear socket. Now, if you do that, and you now get the opposite readings, i.e. the rear gauge is now reading what your fronts been reading but, your front is now performing perfectly, then you've got a serious projected cost ahead of you.

Those MMDCs hover around $450.00 plus or minus. But, if your front gauge still acts the way it does before the hose switch, then you've basically guaranteed it's the gauge. This is the one way I'd be checking the system out if, mine was acting like yours.

Grounds are the top rated cause when there's gauge and electrical issues. But, I don't think your issue is a ground. If you try this little test, let me know how it comes out will you. Good luck.
Scott

One caveat to Scott's suggestion is not to be UNDER the coach and use extreme caution when working under anything that might harm you while working on air issues. You won't believe how quickly your coach will drop by disconnecting even a 1/4 air line. I realize you'll be bleeding off the air in Scott's method, but if something is amiss within your system one of the tanks may not be purged and you'll never get out from under the coach/generator compartment etc. in time....be careful...Dennis

Executive wrote:
One caveat to Scott's suggestion is not to be UNDER the coach and use extreme caution when working under anything that might harm you while working on air issues. You won't believe how quickly your coach will drop by disconnecting even a 1/4 air line. I realize you'll be bleeding off the air in Scott's method, but if something is amiss within your system one of the tanks may not be purged and you'll never get out from under the coach/generator compartment etc. in time....be careful...Dennis

Thanks Dennis,

I most likely should have mentioned that. I forget all that safety stuff. Imagine that! Since I worked in the field of Rescue for my entire career. But yes, you can goof around by trying to drain the system by pulling on the lanyards up front which, may take you 'till next Sunday or, simply depress the brake pedal rapidly, several times and, your air system will be down to nothing in a matter of 15-25 seconds. OH, and if and when you do pull either one of those air lines off the MMDC, and there's any air in the system at all, you might want ear protection and eye protection.

If that air, escaping from those lines, hits debris on the carpet (inside the coach) or anything else, it might kick it up and deposit it in your eyes so, some eye protection for that part of the test, might be warranted too.
Scott

Good info Scott...what haven't you taken apart or played with on that coach?

DSDP Don wrote:
Good info Scott...what haven't you taken apart or played with on that coach?

Don,
Chuckling, you know, without a doubt, this coach is by far the most expensive coach we've ever owned and, BY FAR, I've had to work on this thing in repair/maintenance way more than any other one we've had. I love this coach but, to say the least, it's taxed my abilities to the high end. You ought to see my repair/maintenance/mod/parts Excel spread sheet I created for it.
Scott

Tony,

I have the exact same model and year and had a wiring issue with my MMDC. It is located on the firewall behind wiring looms behind the brake pedal. What Scott said to switch the air lines green and red to see if the problem follows the hose out would be what I would do first.

Good luck.