BAC RV Club Forum
General Boards => Technical Support => Topic started by: Fred Cook on March 24, 2026, 12:55:59 AM
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I have been having problems with my air leveling system. It will initially automatically level fine. But overnight the coach will lean way over towards the driver side. I know I am losing air somewhere, but there may also be a problem with the auxiliary air pump working. I have never worked on a system like this before so I don’t know what that air pump looks like, where it’s located or how to troubleshoot it to see if it even works. Has anybody had any problems like this? It would be nice to have a step-by-step instruction sheet and how to solve this problem.
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I found numerous messages by doing a search using the argument "aux compressor viair". Various messages answer all the questions you asked.
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Thanks, Dave. Just wondering, the coach tends to lean a lot more the colder it gets. Is this a common thing with air level coaches? During warm weather, it stays level for a much longer time.
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From my reading here in the Forum, I would say many, if not most, coaches tend to lean... some quickly within a few hours versus some slowly over a few weeks... and anywhere in between for that matter. Our coach, when parked here over the winter in Yuma has its air dropped, so it's sitting on the bottom of the airbags... thus, no leaning. When in Oregon over the summer, the coach is parked on a down-sloping side-of-the-garage yard with its tail down and nose up. There it will sit for several weeks while its nose will slowly settle down a bit to its curbside. Not much cold weather in our lives anymore!
Only one time in over 13.5 years have I heard the auxiliary compressor running. I didn't know what the noise was and shut it off. lol I later guessed it must have been the auxiliary compressor. And the noise was coming from between the dash and nose, to the curbside of the generator.
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Fred,
It sounds like you may have 2 issues. Do you hear a compressor running at night? This would be the auto leveling compressor that senses low air pressure in the leveling system and turns on to add more air. It's located in front of the steps and is accessible by opening the front cap. With the coach losing level overnght you should hear the compressor running. The OEM (Thomas?) compressors were not long lived. Viair makes a cheaper and more reliable unit if that's one or your issues. I posted a procedure to replace the Thomas with a Viair after I did my conversion. I suspect you also have a leak in the left side air system; Bag, Line, or fitting. Only ways to find it are to hear air leaking (if you are very lucky and leak is significant) or to use a soapy water spray and look for bubbles in the aforementioned components and at the auto leveling compressor. Be sure to block the frame up when working under it. The Leveling section in Coach Assist has info that may be of help too. Also, Common Problems has a comprehensive writeup on the Air Suspension system in the Chassis section. It's located on the same web page as Coach Assist.
Steve
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Steve, are you sure my auxiliary compressor is located forward of the steps on my Patriot thunder? I have looked high and low and everywhere to find that thing and I cannot find it anywhere. It is really baffling. But I will look again to see if I can spot it. Also, what cap are you talking about removing? Are you referring to extending the generator out? I have done that several times and have found nothing. Thanks for your input.
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On our 07 Thunder it is located on a plate under the coach but just ahead of the drive axle. You may be able to see it with a flashlight by looking ahead of the passenger drive wheel but up high.
Yes ours looses air faster in cold weather.
We have replaced the aux. air pump several times and no it doesn’t work even with the OEM from Valid.
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Fred,
Sorry about location issue. I assumed all Roadmaster chassis units were similar. Thanks Keith for correcting me.
Steve
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Well, I have looked everywhere. Even talked to someone who has the exact identical coach as mine, same year and everything. His aux compressor is located behind the front run box so I looked there and there is none there. He and I agree that the previous owner may have taken it out. The coach originated in Arizona where it rarely gets very cold. I suppose I will be putting another one in.
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I remember from years on this Forum that many of us presumed all our coaches were the same, with the auxiliary compressor up under the entry step area, to the right of the genset. That presumption got squashed by those of us chiming in here with an alternate location, as per Keith’s reminder. 😉
Posts related replacing it with a quality Vi-Air compressor.
Joel
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http://beaveramb.org/forum/index.php?topic=3720.0
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Joel, so do you recommend Viair 380C as a replacement? Saw it on Amazon for less than $300.
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I’ve never had to replace my auxiliary compressor, but remember many threads here regarding it, because ours is mounted curbside front like many are, where it’s in harm’s way from road spray/grime. As you may read, the Vi-Airs are less susceptible to that, and others alternatively have made shields for their factory pumps. But, yes, if you search the Forum for other threads I think you’ll find the 380 a common recommendation. Use the Search tab in the menu bar above, not the oft ineffectual Search field at the top right. Try simply “380”, and with “Farris” in the poster’s name field.
You should probably first determine where the factory compressor was, albeit not yet found, so you can utilize any wire and hose infrastructure remaining. There should at least remain a mounting plate somewhere. Also note stouter fusing may be necessary than may exist in any circuit you find, as I think Vi-Airs carry more current.
Joel
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Ours has what i presume is the original Thomas compressor. It is IN the front run box. So, it is not exposed to water or road grime at all. When we got it, it came with a recent receipt for replacing the pressure switch. In 8 months, I have also replaced the pressure switch twice, each with a different style switch. They all seem to leak at the spade terminals so my pump is short cycling and then burns the fuse but the pressure in the tank doesn't ever seem to fall. I'm about to bite the bullet and order the expensive all metal pressure switch from McMaster-Carr.
But, our coach has not yet developed a lean whether the fuse for the pump is in or not. I guess i have that to look forward to...
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Fred, be sure to let us know if and where you find the original pump or its remnants.
-Joel
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Fred,
If you decide to go with a Vi Air, this may help. https://beaveramb.org/forum/index.php/topic,10152.0.html
The Vi Air draws move amperage than the Thomas so be sure to add a relay that is triggered by the check valve and supplies battery 12V via a fuse.
Steve
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Fred, be sure to let us know if and where you find the original pump or its remnants.
-Joel
OK, finally located the compressor. It is on the driver side, even with the front wheel on the inside frame, next to the AC radiator. You cannot see it just by looking underneath the coach. You have to crawl under there and its very hard to see unless you’re practically just below it. Bottom line, the aux compressor works, but sounds very raunchy, and pressure switch is bad. I’m going to replace both. I have seen bunches of them online, but most are advertised for other purposes, like airbrush, air horns, power tools, etc. I believe I will go with VIAIR 444C Chrome Compressor, 200 PSI max. Just need to know what pressure switch I should get for it. I believe it’s somewhere in the range of 100 to 130 PSI?
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Fred,
It's a 120PSI check Valve. Hookup I did is attached.
Steve