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Eng Air Comp Cycles every min
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I know I am asking you to repeat yourself, but this loss of 20 PSI which causes the compressor to recycle only happens when the coach is driven? Never when stationary?
If any of the ball breakers on this site posted this set of circumstances I would say they were playing a joke, but I like you Roger and know you would never make this stuff up
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Just thought of another possible contributing factor. The door air lock. Mine activates when we release the parking brake.
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Thanks Tim, checked the air door lock & pass floor. Not the cause.
No joke Jon, you understand what is occurring. I don’t often look at this gauge while driving other than an occasional glance. I must almost stare at this gauge to see all this activity as it all happens so quick. I use this dash gauge primarily for the aux compressor on pre-start, lifting the bead or opening the dump valves. Just caught my eye on this trip west.
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I’m just going to think out loud here because this makes zero sense.
The engine driven compressor does not fill the accessory air tank. The air filling the tank comes through the protection valve between the accessory tank and the brake tanks.
If that above remark is wrong, someone please straighten me out.
If my remark is accurate it makes my confusion over a potential cause even greater.
The Liberty aux compressor feeds pressure back into the accessory tank I believe via the Liberty installed manifold that is supplied with air pressure from the accessory tank downstream from another protection valve. (I think)
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I am paying attention and don’t get the reference to loss of air at the wet tank while calling it acc. Does he have a gauge on the wet tank.
Looking for 15psi per min steady drop in acc (wet tank)
Let us know how it all works out….
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Tom has a point, but I assumed that if you can see the accessory (aux) pressure you are not reading the wet tank that does not have its pressure reported anyway.
This is the kind of problem that makes people get into the adult beverages earlier in the day.
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The gauge on the dash connects to the accessory manifold which is connected to the acc tank. The acc tank is supplied from the wet tank thru a 75 psi PR-2 pressure protection valve. Above 75 psi the valve is open to the wet tank. Above 75 psi the gauge on the acc tank will follow the wet tank pressure. No check valve over 75 psi. The wet tank is supplied by the SS1200 air dryer, no check valve. The dryer is supplied by the engine compressor, no check valve. This is why the acc gauge on the dash shows the compressor cycling and air dryer purge. It reflects the wet tank pressure above 75psi.
Jon, you are correct that there is a 2nd pressure protection valve in the steering comp which feeds into the Liberty aux air compressor ect…
That is my understanding of the air diagram for this coach.
Thanks for the help
Roger
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Roger,
I think you’ll find a check valve at the secondary supply that feeds the aux tank downstream from the wet and primary tank. Dump the air in your wet tank and see if your aux air depletes. As you use aux air your aux dash gauge does not reflect wet tank pressure due to the check valve.
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Look closer at the T. Line S is from the wet tank. The line marked to the aux tank is before the check valve. The supply from the wet tank feeds both tanks separately. DOT does not allow accessories to be supplied from a brake air tank, primary or secondary. Dumping air in the wet tank will drop the dash gauge until the wet tank is 75-80 psi where the PR-2 will isolate the tanks.
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I hope semantics are not distorting information that might lead to a solution.
The wet tank feeds both brake tanks simultaneously. Until the pressure in the brake tanks reaches the protection valve set point of about 75 PSI air from the wet tank will not pass to the accessory tank. It is irrelevant if the plumbing is set up to use a dedicated line from the wet tank through a protection valve into the accessory tank or if the accessory tank supply comes through a T fitting at or in the vicinity of the brake tank or tanks.
The air is the same regardless of whether its path is from fittings on the brake tanks or direct from the wet tank as long as that path is controlled by the 75 PSI protection valve.
The path of air has nothing to do with the original problem described.
Tom’s question about draining the wet tank is a very good one.
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A leaking air dryer may be the issue. There is usually no check valve between the acc tank and main air line from compressor. The protection valve prevents air passage below 75 psi, but usually air to leave the acc tank to feed the brake tanks if needed. Might be worth a check.
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Air will not backfeed from accessory to brake tanks unless something is wrong.
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I don’t know if your vintage has the Wabco or Haldex dryer, but regardless I have had both types and the amount of air from anywhere to purge is little more than a quick hiss. Maybe a couple of seconds max. But based on everything you told us your loss of accessory pressure has nothing to do with dryer purging, it has to do with driving. You said that engine running, engine off, parking brake on, parking brake off, ride height selected or manual position selected you have only a one minute loss of pressure when driving. We do not know the whole story yet. Something is missing and until that difference between sitting and driving is identified your pressure loss is a mystery.
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Air bags stretch and contract while driving. When driving and the bag stretching can expose cracks and leaks versus sitting still with a compact bag height.
Later
bv
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Yes, driving. Driving fast driving slow but only driving. Stop moving & the compressor cycling stops. After 1 week in the shop, we r back on the road with same issue. Changed 2 check valves primary & secondary, 75 psi pressure protection valve at acc tank & in steering comp, Merritor/Wabco air dryer, R12’s, R14, compressor governor, all new air springs, 6 new Norgren valves, Versa valve, Watts filter/auto drain. Anything that bubbled, hissed or looked like it might leak has been replaced or fixed. An unsolved mystery.
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