Air system question

[Inventor]

1998 Monaco dynasty roadmaster
I am not totally sure what is going on
I had two air bags deflate 100 miles from home and keeping an eye on the pressure stayed around 120psi both needles +/- I made it home ok
now I move the MH one mile to a new location with full pressure and at the end i lost all the air and the brake was set automatically.
Now I don't get any air pumping
I did supply air through the tow inlet to check for leaks and I can only pump in 50 psi when I close the inlet valve the pressure stay constant at 50 psi so I am assuming and am not sure on thay the system not leaking, note here I remove the two bags and test them their we're not leaking
So with out taking parts apart again where do I start testing/checking, motorhome mechanics in my area are not willing

Thank you Mike G

[twinboat]

All air goes thru the air dryer, if its purge valve is sticking, you get the symptoms your seeing.

[Inventor]

Originally Posted by twinboat

All air goes thru the air dryer, if its purge valve is sticking, you get the symptoms your seeing.

Is that it

[Inventor]

Or is it here on the air dryer

[twinboat]

Originally Posted by Inventor

Or is it here on the air dryer

That is the air dryer, it should be serviced every 3 to 4 years.

[Inventor]

Originally Posted by twinboat

That is the air dryer, it should be serviced every 3 to 4 years.

Ok thanks where do i start and where do I find the service info?

[Skip426]

The dryer looks like one of two commonly used by Freightliner ; here's there service info .

Many members opt to purchase a new/reman dryer rater than rebuild their own.

[SafariBen]

If you're getting no air pressure now, then the problem is before the tank, so in the compressor, output hose, compressor controls, or the dryer. If the dryer was the issue, it would be leaking air continuously when the engine is running. The output hose is hard to find a leak on because you can't hear it easy over the engine running, and usually don't feel like putting your hands up there either. If you can pressurize from the compressor with the engine off, that might find an obvious leak that isn't obvious with the engine running. The controls like the governor and unloader are part of the compressor but fail more often than the compressor pistons, cylinder and valves themselves.


I don't understand your sequence of events. If you lost air bags, but the air pressure held steady for another 100 miles, that doesn't sound like the same problem as the later no air issue. Not sure these are the same issue.


edit, and more research shows I'm over my head on this one:

https://www.youtube.com/watch?v=9VM3m0dROV0

https://www.youtube.com/watch?v=LjWQStJxXf8

https://www.youtube.com/watch?v=EAZJuaX1xNM

[Inventor]

Originally Posted by SafariBen

If you're getting no air pressure now, then the problem is before the tank, so in the compressor, output hose, compressor controls, or the dryer. If the dryer was the issue, it would be leaking air continuously when the engine is running. The output hose is hard to find a leak on because you can't hear it easy over the engine running, and usually don't feel like putting your hands up there either. If you can pressurize from the compressor with the engine off, that might find an obvious leak that isn't obvious with the engine running. The controls like the governor and unloader are part of the compressor but fail more often than the compressor pistons, cylinder and valves themselves.


I don't understand your sequence of events. If you lost air bags, but the air pressure held steady for another 100 miles, that doesn't sound like the same problem as the later no air issue. Not sure these are the same issue.


edit, and more research shows I'm over my head on this one:

So I know is confusing to my to so the question is? there is a tow inlet in the front for towing can I put air to prime the system from there? Won't that fill the hole system

[Inventor]

This problem is gering stranger by the day
I plugged in my compressor and got as far as 50 LB in the system thru the tow plugin inlet let the compressor work for 10 minutes but no advance in the pressure, them I dissident to start the engine for 2 minutes running with the compressor and the engine combined nothing! then i run the engine up to 1500 rpm both the orange and green start to move and got to full pressure after couple air dryer discharges I check the two bags that I thought were blown to witch I remove check and reinstalled they were nice and full, At this point I deployd the leveling jacks and the engine went from 600 rpm to 1200 rpm and stay there then I knottiest the air pressure gage down to 50 LB and stay there I shutdown the engine and went to check the bags again their were nice and inflated, I started the engine again and again the rpm up at 1200 and not coming down no air pressure buildup so after revving the engine I managed to lower the rpm to 1000 then I turned the engine off and here I am with my hands up in the air totally confused.

[Cat]

Originally Posted by Inventor

This problem is gering stranger by the day
I plugged in my compressor and got as far as 50 LB in the system thru the tow plugin inlet let the compressor work for 10 minutes but no advance in the pressure, them I dissident to start the engine for 2 minutes running with the compressor and the engine combined nothing! then i run the engine up to 1500 rpm both the orange and green start to move and got to full pressure after couple air dryer discharges I check the two bags that I thought were blown to witch I remove check and reinstalled they were nice and full, At this point I deployd the leveling jacks and the engine went from 600 rpm to 1200 rpm and stay there then I knottiest the air pressure gage down to 50 LB and stay there I shutdown the engine and went to check the bags again their were nice and inflated, I started the engine again and again the rpm up at 1200 and not coming down no air pressure buildup so after revving the engine I managed to lower the rpm to 1000 then I turned the engine off and here I am with my hands up in the air totally confused.

1. One of the best tools to have is a separate air compressor running on house power
2. quiet area.
3. a helper
Get the electric air to full pressure- then get under the MH then have helper plug air line to tow port and listen ( unplug the electric compressor so it very quiet and listen. Start in the rear do the above several times. If you dont hear any leak move forward and listen again. Still nothing move to the inside under the dash-- do same procedure.

Still nothing Block your wheels so the MH will not move-because you will be releasing the brake. Same basic test-- build air up unplug electric air compressor have helper plug in air house to tow port while you hold braking brake release in--- have helper run to rear of motor home knell down and listen for the air leak.
You may have to do this several times- the quieter it is around the MHnthe better.
Hope that helps. Let us know how you come out.
As people have said the air dryer purge is a common leak area. The air bag leveling valve is another. And the air brake quick dump valve is another.

[Inventor]

Ok Thanks BUt please explain this for me
1. why the hose compressor can only pump 50 Lb
2. why after I pump in air then shut off the tow intake valve the air is not escaping stedy at 50 Lb even 4 hours later
3. if there was a leak why did the system was pressurized with the onboard compressor when I got the engine up to 1500 rpm and at list 2 air releases from the air dryer
4. Why the engine compressor is not pumping now on a second try
and finely why I can only put in 50 Lb with any of my electric compressors
You say that "As people have said the air dryer purge is a common leak area. (is not leaking)
The air bag leveling valve is another (don't have one)
And the air brake quick dump valve is another (That is not leaking)

[Cat]

Originally Posted by Inventor

Ok Thanks BUt please explain this for me
1. why the hose compressor can only pump 50 Lb
2. why after I pump in air then shut off the tow intake valve the air is not escaping stedy at 50 Lb even 4 hours later
3. if there was a leak why did the system was pressurized with the onboard compressor when I got the engine up to 1500 rpm and at list 2 air releases from the air dryer
4. Why the engine compressor is not pumping now on a second try
and finely why I can only put in 50 Lb with any of my electric compressors
You say that "As people have said the air dryer purge is a common leak area. (is not leaking)
The air bag leveling valve is another (don't have one)
And the air brake quick dump valve is another (That is not leaking)

.1and 2 it maybe a valve that is unseating at 50 psi and above- but stops leaking at 50 Psi and below. There are many valve in your air system that shifts/ opens or closes at different pressures. This is to safe guard the system.
3 the air systems get full of contaminates water and oil being two them. This can cause and cause valve to sometimes stick and then sometimes work properly. By applying and releasing several times they can become operational then become stuck again. Again this is also not unusual.
4 The MH compressor maybe working but cannot pump enough air because of a leak .In fact the faster you run the rpm the faster the compressor turns which means it pumps more Cubic feet of air over coming the leak. Which would mean the MH compressor is pumping. And because you now over coming the air leak and the pressure builds higher then this higher pressure may shift a sticking valve allowing it seal or even operate normally for awhile.
You are actually lucky the problem is occurring often. This allows you to take the time at home to find the problem. There is nothing worse than having this problem once in awhile on the road.
Hope this helps.