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Aux Air Compressor Cycling Every 2.5 hours
The aux air compressor in the generator bay of our coach is cycling on every 2.5 hours for 45 seconds and then turning off. Is this normal? Is the aux air used for anything other than air pocket doors and the like? After the aux air cycled I checked the belt tensioner for the engine fan and it was still at zero psi. Is there a way to air up the belt tensioner air bag BEFORE you start the engine?
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25 Replies
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In my CC I have an on/off button for the air Aux compressor. I have found in my bus as i have fixed leaks currently there is no reason i need the aux compressor to run. When i first got my Bus, i needed the aux air at 100 psi to keep the bus level which was a challenge because i had suspension leaks ans aux air leaks. Once I replaced all my air components my bus will sit level for weeks, with my aux air dropping about 10 psi per 24 hour period. I don’t have air pocket doors, or a belt tensioner. Since you are mentioning your belt tensioner is at 0 psi, maybe that is the leak path? There should be a check valve trapping air in your belt tensioner, and an actuation valve in the driver bay to release tension to change the belt. My guess is they put the regulator between that circuit and the aux air tank? On my bus it was harder for me to chase down all my aux air leaks than it was all the other air components like brakes, bags, valves, fittings etc. Maybe someone with your model year has other input.
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Your 2.5 hrs is not unusual, you do have leaks in the aux system. To charge the engine belts with air before starting, you turn the yellow valve in the steering compartment to merge your accessory air with the Prevost chassis air. Keep in mind your aux compressor makes a lot of water, so be sure to drain off water often from the aux tank before introducing aux air to the Prevost side. Close the valve after charging the belts.
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Tom, that reminds me, I had exactly that problem when i first got my Bus. I added a 5 Micron auto release water trap at the exit of the Aux compressor. See the picture attached, you can see some moisture in the bowl, this is after a 48 hour cycle of the compressor running at 100 PSI kick on and 120 PSI kick off. Temps were 85 degrees during the day and 65 degrees at night. I also have an Aux air water trap in the steering bay that i replaced to an Auto drain. Mine was original to the Bus, the filter was a spool of thread and not auto drain.
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Larry! The Aux system does all the air to everything except the brakes, So driving down the road the level system gives you ride height, level low when parked to level, belt tenisioner’s on Detroit, generator air bags, foot well slide, pocket doors, toilet if you have air toilet, sewer dump valves and any other air things. When we park we don’t need any air,We Changed toilet right away no air pocket doors, Generator air bags are by their self 2 schrader valves I add air once a year, Bus stays level.Detroit belt air bags stay full for months, So when I fire it up belts are always tight, Their is a check valve up there above valve with red knob, I got rid of the red knob valve because it leaked and I put 1 1/4 inch ball valve in line, If I need to change a belt I turn the ball off push schrader valve belts are loose, turn ball valve on belts are tight. That red knob valve was $250 bucks I couldn’t talk myself into that, I made it simple. My compressor Never gets turned on. Larry when you drive watch your aux gauge probably slowly drops to 100 psi then governor kicks in and gauge rises to 120 psi if it’s slow no big deal, Mine at 1st was every couple of minutes, now it stays put I got rid of most of the bad leaks.
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Larry,
Marathon is the only converter that isolates it’s Aux air from Prevost Air. Your belt tension is aired on your Prevost side. Tom told you how to fill your bags if you choose with the yellow valve in the front run box.
All house items are on your Marathon aux side, none of it comes from the Prevost side unless you open the yellow valve which you should not do.
People trying to help is good but but none of it is relevant unless they know how a Marathon is plumbed.
Later
bv
1999 XLV X-6872, liberty #440 -
Ditto what Bernie said, I was commenting Marathon specific.
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Thanks all for your input. Since this is a Marathon we’re talking about some further clarifacation may be in order here. Tom says it’s okay to air up the belt tensioner with the little yellow valve and Bernie says “which you should not do.”
That’s like straddling an A bomb and having the two bomb techs on the radio telling you how to disarm it and one of them says “cut the red wire” and the other one says “uuuh I’m pretty sure it’s the black one dude”
Just heard the aux compressor turn off and checked the aux gauge on the dash ands it’s flatline. No pressure at all. How are all the air items in the coach functioning (stairwell slide, commode door, bed lift and most noticeably of all the coach is still level.Bernie, since the airbags are part of the Prevost equation (I think) how are all these things working when the guage reads zero. So confusing…Tom, I’m attaching a couple of pics just to make sure we’re all on the same page here. Two possible things I can turn and probably snap off showing. Tried turning the steel one attached to the copper tubing and nada. Nothing came out. No water, no air…nothing. Now I’m contemplating turning the plastic valve on the bottom of the item labeled Norgren which I’m almost certain will snap right off.Are either of these what I need to drain before I clip the red wire…uhh I mean turn that yellow valve and blow myself to bits. -
Great info about Marathon being the only converter to isolate those. Does that mean he has 2 leak issues? A leak in his Belt tensioner circuit and a leak in his House Aux air?
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the valve you spoke of on the norgren air filter is there for you to drain regular. keeps moist aux generated air—- from your primary and secondary coach systems. The aux system leaks( before that filter) can often be caused by a bad check valve. I like your pictures.. The push fittings are a major source of leaks as weather (temp) changes. use compression fittings.–(as you need to replace them..
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I should of been more clear, yellow valve should be closed after you air up belt tension, that leak is probably the check valve by the red switch above the motor to release pulley pressure.
The gauge in the front run box is your Marathon aux air. Dash gauge has nothing to do with that.
When you turn off the key air is locked in by the norgren valves so if no leak between valve and air bag you won’t lean. Dash Prevost aux gauge can read zero.
On your coach if you join both air systems (open yellow valve) you may have to turn key 1 click to the right to allow air in.
I’ll go deeper in the morning.There is a ton of info on this if you go into old posts and search.
Later
bv
2015 we talked about this a lot
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The valve in your first picture circled in red is the Prevost aux tank drain.
The Norgren drain is for the Prevost side as Robert noted.
The Marathon aux auto drain is the the clear sight glass with two lines attached and probably doesn’t work unless maintained.
Bernie expanded on the yellow valve, open to charge bellows then close.
You need to find your Marathon aux tank and drain the water often. My 02 H aux tank was behind the front bumper.
2000 Featherlite H3-45
2024 Jeep Grand Cherokee
Leesburg, FL -
Regardless of who the converter was for your coach it is very important to know and understand how your coach pneumatic system is plumbed.
Water is the enemy of the pneumatic system and regardless of who built the coach or how the air is routed through it moisture in the system has to be trapped and removed. If it enters the pneumatic system (and it will) the resulting issues can defy all logic and make a logical analysis of problems difficult if not impossible.
There are and have been coaches that have never had air dryers replaced since new, air tanks that have never been drained, and auxiliary air traps or dryers never serviced. Ca-ching, Ca-ching.
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Bernie…my man…I should have you on speed dial buddy! Thanks for that very detailed post. Tom, I have been trying to figure out how to open the front bumper on this thing since we bought it. I just figured I’d wait till we got to Marathon to have then show me. I really want to try your suggestion and fill the fan bellows from the aux tank but its been raining here none stop all week and with the aux pump cycling every two and a half hours there’s bound to be a lot of water in there. To Johns point when I took that class at ETLC it was made crystal clear that draining those tanks is one of the most important things you can do as part of routine maintenance but I still haven’t been able to locate all the valves to bleed the tanks.
The reason I’m so concerned about airing up the fan tensioner is because when I was checking the oil the other day, I realized that I’m currently only running with two belts and it clearly looks like there should be three. Okay you can all stop laughing now. Not only that but at the fan end both belts are on the pulleys closest to the rear of the coach and at the crank end they’re on the two pulls closest to the engine. Okay you can all get up off the floor, it’s not that funny, (okay it’s a little funny). I started the engine from the rear control panel last time to see (and hear) how the engine cranked over after I replaced the chassis batteries and installed that trickle charger (another story…another day) and when it started those belts were wobbling like crazy until the tensioner aired up. I spoke to the previous owner to see if maybe there was a reason it was set up this way and he said “well that’s the way it was in the pictures in the ad” So basically it’s your problem now, no real explanation just “the coach was sold as is” kinda vibe. Don’t know how I could have missed something glaringly obvious for this long but here we are. I have spare belts with me but I spoke to Prevost about the situation and they said keep an eye on the belts for increasing wear for now but all three should be replaced together and the belts were probably in their proper pulleys at some point but the fan gear box may be misaligned which due to the slack belts at start up the belts skipped over to the other pulleys. Okay I can hear the laughter from here, now you’re just being cruel. We’re leaving the Oregon coast today and the next stop is Marathon so for now I’m just filing this under “if it aint broke, don’t fix it’ and I think I just heard Jon fall off his chair.
So now you see why I’d really like to have those belts tight before I kick over the engine. Tom, if you can help me figure out how to get that front bumper open to see if that’s where the aux tank drain is I’d be much obliged. -
Bernie and Tom are correct. My coach is the same vintage as yours, when I bought it the Marathon aux compressor would run every 45 minutes. (Not Al’s fault Bernie, the dude that owned it between us had no idea what he was doing) After many, many, hours of leak hunting it runs maybe every 72 hours. I suck at typing so give me a call at 402 658 9437, i can walk you through all the leak sources and fixes.
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On my coach (2003 chassis), the release is in the driver’s bay. It is a handle attached to a cable, and it is labeled. I suggest that you have someone support the bumper when it is released until you gain confidence that the bumper descent is slowed by operational springs, that that the descent stops before the bumper hits the ground.
When I purchased my coach, I got schooled on how to release the bumper by Tom himself. I had my head way up in the driver’s bay while I was telling Tom that the seller had showed me the bumper release was “somewhere in here.” Tom pointed to the pull handle (which was labeled “bumper release,” or something like that), and said “it’s right here.” He did not call me a “dumbass,” but he was thinking it.
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