Compressor Air Problem Continued....

[Iver]

   I have been using all the suggestions you have kindly recommended to check my compressor.

This is the latest situation.  Started engine, air built very slowly but finally the compressor unloaded and the air dryer purged.  I pumped down the brakes until the compressor loaded again and the air started to build again. The dash gauge stayed up but I checked the air gauge at the air drain valve at the back and it said zero air pressure.  I turned the engine off.

So, I hooked up shop air to the line in back and I heard air (a lot) leaking by the wet tank. I couldn't tell exactly where from.  The air gauge on the dash remained basically constant.

I decided to move the bus over my pit to check where the leak might be coming from.  I turned off the engine, listened for leaks. (none).  Now the air gauge in the rear reads 115 and holding.

What could cause intermittent air leakage in the wet tank system? 

         Thanks for the help,   Iver.

[Iver]

Ok, I think I found a leak.......I used shop air to build pressure up in the bus until the air dryer purged.  I turned off the air and discovered the air dryer was still expelling air.
     Is the valve on the bottom of the air dryer replaceable?  I guess I should check/change the dessicant at the same time?
     Hopefully I won't have to change the compressor after all.
Thanks for everyone's help,   Iver.

[buswarrior]

Did you still have the shop air hooked up?

The air drier purge valve vents the air drier cavity, and the line back to the compressor. Under normal conditions, the governor has signalled the compressor to stop pumping as it signalled the drier to purge, so no more air being supplied.

With the shop air connected, you will get continuous air out the bottom of the drier when it is purging.

And you will not be able to raise the system pressure from the engine room fitting with shop air if the drier is purging, as the air can't get past the drier's valving in that configuration.

Keep us in the loop!

happy coaching!
buswarrior

[Iver]

Oh Shoot.....
    I thought I had it figured out.  So it is normal to see my gauge at the drain line drop to zero after the dryer has purged?   
    My original problem was slow building air or no air with the engine running.  It is almost impossible to hear any leaks then.   After the dryer purged, I checked the rear air gauge and it read zero.  If as you say the dryer vents the line back to the compressor then the gauge would read zero.

    I can't help but think that something must get stuck open because my original problem came after I pumped the brake air down to zero, the compressor would not move the gauge on the dash. 

    If I apply shop air to the drain connector, I can build air up to 100lbs.(without the dryer purging) and it will gradually leak down in about less than an hour.
    What more testing can I do?

[Brian Diehl]

One thing to do is start checking every air pressure regulator.  When I first got my bus it would leak down to zero in less than an hour.  I thought I had a single big leak, but it turned out to be lots of small leaks.  Every pressure regulator in my system leaked air around the diaphram.  The other thing to check is if you still have the radiator shutters you should make sure there are no leaks in the lines to the shutter control pistons.  I found on mine one of the copper pipes had come loose and had worn through creating a small leak.

HTH

[Sojourner]

Iver....using shop air if for checking plugged or leak in line or location only.  Due to few check valves in the system, you are going confuse yourself using the shop air for pin point to trouble shoot.

Buswarrior is right if you hold air pressure against the purge valve piston. It only momentary air pressure from the governor in the normal mode.

You need to read the following link well so you can under stand what is ok and how to pin point between compressor and AD-2 dryer. Hope you have done all the checks as per manual.
Bendix® AD-1™ and AD-2™ Air Dryers
http://www.bendixvrc.com/itemDisplay.asp?documentID=3604

Bendix® D-2™ Governor
http://www.bendixvrc.com/itemDisplay.asp?documentID=2382

Bendix Compressor
http://www.todaystrucking.com/images/BendixCompressor%20TroubleshootBW1971.pdf

About air leak down in an hour.....did you have it jack up a little?...levelers will bleed until adjusted height.

Otherwise, fill hand squirt pump bottle with a table spoon of dishing soap and the rest water. Shoot at possible leak and wait a few seconds for tiny bubbles are a sign of slow leaking.

Hope you find it soon and gain more knowledge that is very valuable in the future.

FWIW

Sojourn for Christ, Gerald

[Iver]

Ok, I guess I will have to do more testing.   My coach has a separate leveling system for the air bags and they stay inflated for weeks.  The air pressure reading on the dash drops slowly over 3 days or so.  For the last several weeks it has been working just fine.

My main problem started when after a short drive and stopping the engine, then restarting, and the compressor would not kick in.  I pumped the brake pedal down to zero air with the engine running and it still would not recover.

The last time I started the engine to move the bus, the air seemed to fill ok. Once the compressor unloaded, I pumped the brake down and the compressor loaded again as normal.

Does the compressor fail slowly?   I may have some minor leaks in the system but nothing bad enough to prevent the compressor from building air.

All I can imagine is either some valve is occasionally sticking open or else the compressor is starting to fail......

But,  I am open to any and all suggestions...........Thanks,  Iver.

[gumpy]

Buswarrior is correct about the dryer. It will continue to vent after it purges. To counter this with shop air, simply install a pressure regulator on your air hose, and set it to 100 psi. This will keep the bus air from getting to 120 and purging the dryer and unloading the governor. It will remain a constant 100 psi, and you can then start squirting all the air fittings, devices, and hoses.

Make sure you squirt any braided hoses along their entire length. Often they will crack inside, and you will not know it is leaking through the braiding.

My biggest air problems right now are my baggage bay door locks, the valve that controls them, the wiper valves, and the shutter regulator in the engine compartment.

Like Brian, I had problems with regulators leaking, hoses leaking from the middle, engine control cylinders and skinner valves, airbags, and air beams. I've replaced many hoses and other components, and have much improved performance with my air system.

craig