If you drive a Class A diesel motorhome, eventually you are going to experience an air leak. An air ride motorhome has a complex system of hoses, tanks, bags, connectors and an onboard compressor that keeps the air bags at proper height and maintains the pressure necessary to operate the air brakes as well. Since the compressor runs continuously as you drive, a small leak is usually overcome by the refilling of the tanks — but a larger leak will leave you stranded.
In a correctly operating system, a short stop for dinner, or even after a few hours or days, the system should be at or near normal air pressure. Even a week or two can yield good pressure as you restart the coach if the system is really “airtight.” If you start up after a few hours or days and are greeted by the chassis low air alert, the likely cause is an air leak. Fixing the leak is not usually as hard as locating it, but if you can find it, you can probably fix it.
There are numerous causes for air leaks, and they can emanate from a variety of sources, but if you do a little investigation of your own, you can likely identify all but the smallest of leaks. This particular coach when new could sit a week or more and never leak down enough that the low air alert would sound. But lately we noted that an overnight or long rest stop resulted in the pressure dropping to a point where the low air alarm would sound on start up. It never caused an operational issue, as the pressure stayed up while the engine was running, so we knew that it was a fairly small leak and hopefully one that we could find.
After returning from our last trip, we shut down the coach, and while unpacking the storage bays, the sound of leaking air could be easily heard. Since the sound came from the basement, that is where the search began. With nothing other than some courage, a flashlight and reading glasses, it was time to end this annoyance.
When searching for a leak such as this, the coach will need to be aired-up. So if you have been parked a while, you will need to run the engine until you hear the air dryer valve activate. This will ensure the system is at max pressure and will make locating the leak that much easier.
The first step was to unload the storage bay where the leak was heard in order to get access to the “tray” that usually houses all the air lines. These lines route from the compressor in the rear of the coach to the front where the air tanks, front air bags and brakes are located. Most chassis manufacturers use some form of a tray or a large wiring loom to protect the plastic air lines, and they usually locate them along one of the frame rails.
After 20 minutes of unloading, the first thing noted was that we carry too much stuff that we never use, but that’s the topic of another article. The next thing noted was that the storage bay was in need of a good cleaning, so out came the shop vacuum. With the bay clean, entering and exiting could be made without the risk of a stray fishhook making an unauthorized catch. With the coach at full air pressure and the storage bay cleaned out, the leak could be pinpointed, and as expected it was inside the basement.
Every leak may not be as easy to find as this one, and every repair may not be a failed hose, but from our experience, it is usually a leak in a hose, a failed fitting or valve. Using the steps in this article, you should be prepared to tackle an air leak and keep the air bags from leaking down, just as we did.
After our repair, the coach stayed at normal pressure for almost a week, which is more than enough to meet our criterion of a tight air system. If you have a failed valve, or other, more serious problem, you may require professional assistance, but many of those annoying leaks can be fixed at home or even on the road.
E. Don Smith is a Tennessee-based freelance writer and photographer who has been a frequent contributor to MotorHome since 2006. He is the proud owner of a Tiffin Phaeton coach.