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Old 01-21-2021, 12:37 AM   #1
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Air system wont inflate past 35 psi

I have 2003 allegro bus 40dp, I cannot get the air tanks to refill past about 35psi (keeping me stuck) after start and being level on jacks. This happened once Thursday but I turned off key and restarted and it worked properly. Yesterday, however it didn't work. I've researched a bit and tried turning on/off key 3 times and cycled the jacks to level and store twice and these tips from previous write ups didn't work. I noticed that the purge valve on my air dryer was constantly relieving air, so I thought that was the culprit and put a new purge valve in, new pressure relieve valve and a new desiccant filter (even tho it was 8 months old) I was surprised that when I took off the filter, there was a large amount of white powder and white chunks all over inside the housing. I cleaned all that out and reinstalled everything. Now the pressure still won't build past about 35 and at least no air is escaping from the purge valve constantly like before but that wasn't the fix. All the fuses in the HWH 625 panel were good. Only thing I can think of is maybe a dump valve that is stuck open???? but not sure where that is and can't hear any unusual leaking when under bus with it running. Any suggestions??? trying to avoid calling mobile mechanic to me and don't want to tow it!!..thanks...

still stuck, but here's an update: Yes, my desiccant filter came apart and spewed white powder into system..I rebuilt air dryer today, blew out line from air dryer to primary tank (had a ton of white powder come out). Also bypassed the air dryer completely and the primary tank built up past 100 psi but had an awful knocking sound coming from somehere near the rear of the primary tank but unable to pin point. checked ouput of air dryer (before hooking up line to air tank and got good pressure coming from compressor and through air dryer so I think that is good now. But when I hooked up all lines again, it won't build up past about 35 psi on tanks going through air dryer...couple of questions:

1) the air line from the air dryer-where does it go? to the primary tank or a manifold or ck valve or something first.
2) I blew out the front two air bags with compressed air after disconnecting the blue lines and saw no white powder, so it didn't breach them...
3) What else should I try and access or blow out to try and get it to go past 35 psi when all hooked up?? remember the primary tank got up to at least 100 psi when I bypassed the air dryer but the air dryer is rebuilt now and does output air when partially hooked up..

gonna see if mobil tech can come out in morning if I don't get any more advice here but if sounds familiar to anyone please advise.

.thanks!!
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Old 01-21-2021, 01:34 AM   #2
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Sadly, nothing to offer. I hardly see questions here about air problems. If so usually just leaks. Please keep us posted. When you say you rebuilt air dryer, do you mean you just cleaned it out, or did you replace parts, like o rings etc?
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Old 01-21-2021, 04:58 AM   #3
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I went through something like that, mine turned out to be a small air line from the controller to the compressor that had a hole in it. My problem was the opposite, this allowed too much pressure and also kicked the high pressure relief on the dryer. The dryer was unservicable in my case and I replaced it.

I doubt yours is this easy but it is a start. This was when I first bought my unit and the wet air tank was perhaps half full of water.
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Old 01-21-2021, 08:58 AM   #4
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If you are suspecting an air leak in the system, it is difficult to locate with the motor running. With the motor off air up the system with the tow connection. (usually near the front). This will allow you to locate a leak if that is the case. Soapy water in a spray bottle also is a good way to locate a leak. Good luck as they can be hard to find.
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Old 01-21-2021, 09:17 AM   #5
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….fact that desiccant bag ruptured, kind of put this in an all new category--few of us have ever experienced this, but it does remind us that periodic maintenance of the air dryer is critical....Curious, how cold is the ambient temps--if below 40 degrees, were you able to confirm that the value heater on your new air dryer is working properly--eg, is your rig providing 12v power to the dryer?
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Old 01-21-2021, 09:29 AM   #6
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air system contaminated??

Mile Marker,-- I installed a new cartridge, dessicant filter, pressure relief valve, purge valve and cleaned and inspected the turbo check valve (couldn't replace as no one had that part around here but it looked ok) basically kit DQ 6026 plus the plurge valve, however much white powder went down line towards tanks so I think thats whats messed up but just don't know what valves, solenoids or check valves to take off to inspect clean etc....

old scout, just changed the desiccant and cartridge 8 months ago and in phoenix area so temps are above freezing

not sure it's a leak in a line as i bypassed the dryer and pressure in tank was building past 100 psi

could it possibly be the governor off of the compressor?? I doubt it as it builds w/o going through the dryer, but when I put the dryer inline then it only goes up to 35 psi
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Old 01-21-2021, 10:36 AM   #7
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“ just changed the desiccant and cartridge 8 months ago” No good deed goes unpunished.
“ bypassed the dryer and pressure in tank was building past 100 psi” to me that means it’s the dryer IF the line to the Governor doesn’t go from the dryer.
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Old 01-21-2021, 04:18 PM   #8
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air pressure won't build past 35 psi

Just wanted everyone know what the fix was:: Got it fixed and driveble today..Turned out that the compressor governor was also bad. We don't know if the Air dryer went out first then the white powder in system smoked the governor or if the governor went first smoking out the air dryer..But what I learned from all this is that if the air temp out from the compressor / governor to the air dryer exceeds 170 degrees then it will destroy the desiccant filter causing all the white powder substance to go into the system! Best thing about all this was that it cost only 243.00 and about 2.5 days of researching and wrenching..(No labor costs!!) Had a great tech from Haldex today that figured it out and did the correct troubleshooting over the phone...
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Old 01-21-2021, 04:50 PM   #9
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Dang I had the right answer but missed the post in time to help. But anyway did the air temp get too high do to compressor running too hard. I didn't catch reason for killing desiccant filter.
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Old 01-21-2021, 08:56 PM   #10
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air pressure won't build past 35 psi

Yeah, thinking it may of been we had to raise coach on jacks and dump system and re raise coach multiple times in a row with compressor running for a lengthly time period or high rpms during the time trying to get un-stuck in the sand in Glamis, CA
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Old 01-21-2021, 11:27 PM   #11
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Quote:
Originally Posted by ALWAYSSUMTIN View Post
Just wanted everyone know what the fix was:: Got it fixed and driveble today..Turned out that the compressor governor was also bad. We don't know if the Air dryer went out first then the white powder in system smoked the governor or if the governor went first smoking out the air dryer..But what I learned from all this is that if the air temp out from the compressor / governor to the air dryer exceeds 170 degrees then it will destroy the desiccant filter causing all the white powder substance to go into the system! Best thing about all this was that it cost only 243.00 and about 2.5 days of researching and wrenching..(No labor costs!!) Had a great tech from Haldex today that figured it out and did the correct troubleshooting over the phone...
Where is the compressor governor located, on the compressor? Easy to get to?
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Old 01-22-2021, 08:51 PM   #12
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air pressure won't build past 35 psi

Yes, attached to the compressor on my 400 ISL by only two bolts, not easy to get too, had to drop the exhaust to create a small cubby whole that I could partially get up into (and I'm 240lbs) Rig up on hyd jacks and supported by jack stands for additional safety.. the guys that I bought the governor from (freightliner shop) said that the governors only last 3 to 4 years!. not sure how true that is but seems short lifed and they said alot of drivers carry a spare with them...
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Old 01-22-2021, 08:59 PM   #13
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Quote:
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Yes, attached to the compressor on my 400 ISL by only two bolts, not easy to get too, had to drop the exhaust to create a small cubby whole that I could partially get up into (and I'm 240lbs) Rig up on hyd jacks and supported by jack stands for additional safety.. the guys that I bought the governor from (freightliner shop) said that the governors only last 3 to 4 years!. not sure how true that is but seems short lifed and they said alot of drivers carry a spare with them...
Thank you! Boy, if I carried a spare of everything that wore out every 4 or 5 years, if have a coach full of parts. Lol
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Old 01-23-2021, 07:31 AM   #14
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“ the guys that I bought the governor from (freightliner shop) said that the governors only last 3 to 4 years!.” BS. I have a 1984 dump truck (owned since 94) and the governor is definitely 26 and probably 36 years old. I carry plenty of spares but a governor is not one of them.
04 Dynasty’s is 16 years old.
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