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Aux. Compressor making air dryer purge
I am new to PC but have owned a coach for long enough to know that I cannot keep everything working at the same time. Its always something.
When I park the bus to stay overnight and use the auto level feature to level the coach, I pull the parking brake, switch the motor to high idle and wait until all the solenoids purge off and stop making noise. Because of my OCD, I switch the level button back to ride height partially filling any airbag that completely dumped so Im not leaving the coach with a bottomed out bag (not enought to make the coach unlevel again) then turn off the engine.
As soon as I switch the button to ride hieght the aux. tank pressure goes down and the aux compressor kicks on. The compressor starts to fill the aux. tank back up to about 95lbs then I hear the air dryer purge (key is off, engine is off). The compressor keeps running and the dryer purges again and again so i just shut the compressor off.
In the morning I turn the aux compressor back on, start the bus, turn the high idle on (exactly 2 minutes after starting to make sure the turbo is well oiled) and wait for the coach to reach ride height. Everything is good to go.
Basically, when Im not trying to level the bus and just park it, the aux compressor cycles and shuts off normally. Is there a valve that is not closing all the way causing air to back feed to the dryer or what?
To be more specific, its the main dryer with the spin on desiccant filter located above the drive axle that is purging. Not the Norgren water trap or anyting in the steering compartment.
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3 Replies
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I won’t get into your leveling process because there is something you said that is far more significant and does need checking.
I interpret what you are saying as your aux compressor is causing the Prevost installed air dryer to purge at the end of a cycle. If that is the case something is seriously wrong and needs attention. It may even be a serious safety issue.
The whay our Liberty coaches are set up we draw accessory air for various house functions. But we also have chassis functions that require accessory air such as the suspension. With the engine not running our two brake systems should remain at whatever pressure was showing when the coach engine was turned off. The accessory tank pressure is going to go up and down depending on what air is being used by the various functions (or leaks). When the pressure drop causes the aux compressor to kick on it should pressurize the accessory tank only, and should never ever pass through the air dryer you say is cycling. When the accessory tank (aux) compressor cut off point is reached it should shut off. If it is the normal compressor supplied by Liberty, it has a max pressure rating of 100 PSI.
Did I understand your comment correctly?
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You are correct. The aux. compressor is and has caused the main compressor dryer to purge ONLY when the low level setting is on and the coach has self leveled. At least I am assuming it is causing the dryer to purge b/c the engine is off and the only thing running is the aux. compressor. The aux. compressor is the one Liberty installed (Gast I think) originally with the well type switch.
With that, when I bring the coach to travel height, there is no drop in air pressure on the primary or secondary guages. It is only the aux. guage that goes down.
In my mind (theres a scary place to go!) there is no way the aux compressor can purge the dryer. The dryer only gets the signal from the governor as when to purge. Furthermore, the air can only go from the compressor, through the dryer, into the wet tank, filling the primary, then secondary with check valves keeping the air from ever going backward right? Where would the aux. air even be connected in there anywhere?
BTW, Is there a correct procedure to level the coach or is it the residence’s preference?
Thanks Jon.
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Patrick,
As you correctly surmise something is very wrong because there should be no way to get accessory air to the upstream (inlet) side of the dryer. Clearly it has to be confirmed that it is the accessory air via the aux compressor that is making the dryer purge. If it is someone has been screwing with the system and it needs to be restored to the original condition.
An opinion on the second part of the original post is my interpretation of how to level with the Liberty suspension controls.
We are in full agreement about your use of the auto level. High idle helps because if part of the suspension has to be raised you can build or retain air pressure because of the higher engine RPM.
But even if the leveling drops the coach it does not completely purge all the air in the air bgs unless it is lowered to the absolute bottom and that still is not enough to get level. Only under that circumstance will all air pressure in the respective air bags be exhausted and then you will not hear the Norgren valves close. Air will just stop leaking out because it will all be gone.
So when I am auto-leveling and the coach is where it is going to be, I just turn off the key. At one time it was suggested to switch to the driving position and then immediately turn off the key, but either way what should happen is exactly the same, and that is all Norgren 5 port valves will go to the normal position which closes off air to or from the air bags.When you turn off the key the aux compressor if it turned on may run, but if the engine has been running for a while after you level the coach and you do not need to keep the aux compressor on for any other purpose, why bother to have it on at all? The engine driven compressor should have been doing all the work for leveling. It concerns me that you seem to indicate the aux compressor is running when the engine is running.
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