[Archived]

I have zero experience with a Marathon, but generally speaking it is likely you will have a dual valve or a pair of valves that control door operation. One to supply air to open the door, one to supply air to close the door.

If one or both are leaking you have to either find and repair or replace the valve. I doubt if Marathon isolates its auxiliary air devices from the Prevost auxiliary air system so that leak is going to have an effect on the operation of your coach, possibly to a great extent if the leak is significant.

Turning off the aux compressor is the right move initially because it will literally wear itself out if it cannot keep up with the leak. But if the leak is big enough it is going to do the same to the engine driven air compressor. While we consider air for the brakes as most important, we cannot overlook the importance of aux air pressure either. The air suspension is the big user of aux air, but so are the belt tensioners, the retarder, and your seat.

Then there are the house devices that use air, including floor slide generator air bags, bed lift, pocket doors and possibly the awnings and toilet.

The point is you may not need to make a repair right now, but the thing I would recommend is to at least cap or plug the air supply to the valve so all aux air systems and devices can function as needed.

Perhaps some Marathon owners can jump in and tell you where Marathon routes the air line to the pocket door valve(s) so you can access it and shut off the air.

FWIW on my last two coaches I added shut off valves (manual) to every house aux air line so if I need to shut off any of them I could. I also use the valves to shut off air lines when looking for leaks. After a few minutes I turn them all back on, one at a time, and the one I hear air flowing into is the one with the leak. I haven’t figured how to do that on the chassis aux air system yet because the routing of those lines is not so conducive to a set of valves easily accessed in one spot as the house valves were.

[Archived]

Threegreens,

With my many adventures to end air leaks I learned the ways of Marathon.

I pictured our adjustable regulator bank on my bus under ……..Air leak repair.

There are a few years difference in our Marathons. Chances are you have something similar to our coach. Marathon tech service states supply lines run complete from source to use junctions. Marathon then mounts a regulator for the proper air pressure needed to function that piece of equipment. Then mount an electric knife switch, mounted next to the regulator …press the button, switch opens… regulator has been adjusted to 60 psi and air door moves.

Some place on the inside of your bus is the regulator bank for the aux air devices. Ours was in the rear bedroom behind the storage drawers. 4 labeled to ID the system. One labeled “air door”.

Locating the regulator will give you the option of closing the air supply to your door system. You can then turn back on the Aux compressor allowing use of the other air operated items.

[Robert]

Thanks for all the pointers and ideas.

I might be lucky (for once). It looks like on our coach the only use for the little aux compressor is the bathroom door and the footwell slide. I always wondered why Marathon isolated the little compressor and its pancake tank via valve from the coach aux system. Now I know and am glad they did. I’ll fire up the engine to make sure the aux air system is tight before we leave.

Another mystery is that the bathroom door still works even without air. It opens and closes except for the last 0.5 inch soft close. I am at a loss to explain that.

[Bob]

I would be extremely surprised if Marathon dedicated a small compressor just to provide air to a pocket door and floor slide.

Unless those are the only two pneumatic devices on the conversion side of the bus.

If the coach has any of the following it is probable the aux air compressor either ties into the bus aux system or someone has made modifications: bed lift, air horns, driver seat, generator air bags, air operated dump valves, rear camera cover, toilet, awnings that use air, or a toy such as a train horn.

Easy to confirm. Take the aux air pressure to zero and turn on the small aux compressor to see if it brings the aux air pressure back up.

[Jeff]

I’ll take a WAG (wild ass guess) on why the air door still works.

There is a check valve some place in the system that is not sealing or a defective air manifold.

Have you located the air regulator for the doors ? Air is being supplied from some source. With the compressor running it has a cut out pressure of 120 lbs. With the air doors on my bus I believe the air regulator is set at 60 psi to move the door. Air is called for when you touch the button…re: knife valve.

I agree with Jon; A) more then 2 devices are running off a single compressor and tank.

B) Taking tank to zero then restarting to determine where the air is going.

[Larry]

Thanks everone for your pointers. We were able to complete the trip by just turning off the little air compressor below the driver seat. Doing so we had no air slide (foot well) and no air horns which was as expected.

Today I fired up the compressor and to may surprise the bathroom door is now fully operational again. No loud leak in the wall. I speculate that the electric/pneumatic valve that operates the door was stuck open that night. But now it works again. Pneumatics are fun.

All is not well though. The horns still do not work and the air slide only retracts very reluctantly. I hear some faint hissing coming from the slide pressure regulator (set at 60 psi). I plan on taking it apart and cleaning it.

The other concern is the air compressor. Its supply leads get very hot when running.Too hot to touch. It actually melted the connector covers. The compressor is rated at 18 amps at 12V. It must be pulling more than 18 amps. I’ll look into an overhaul kit or replacement. It is a Thomas Industries 315 series compressor. Has anyone found a good source for them?

In the picture you can see the melted connector covers (black) on the compressor side.