-
Need Help Again – Is Air Dryer Failing?
Greeting from our Nation’s Capitol,
We are on the 3rd leg of our maiden voyage in our new to us 2007 H3 and while at a rest stop with the engine running at high idle, noticed the sound of the air braking system air dryer purging approximately every 30 seconds to one minute. Yes…super frequently…sometimes as soon as every 10 seconds…
Upon continuing driving to our campground where we will be for the next 7 days, I watched the air tank gauges even more closely than normal and discovered they only dropped a VERY few PSI (hardly noticeable) before the system would pressurize back up to about 120 PSI.
NEVER did the air go down to say 90 psi, then pressure back up to 120 which was the case on my two previous “plastic coaches”.
This bus has a discontinued Haldex 91787 Air Dryer and the dessicant cartridge was changed as part of the very recent pre-sale PDI.
Has anyone experienced such frequent purging of their air brake dryer? Thoughts on whether or not the dryer needs a rebuilt kit? Replacement? OR if the problem is with the compressor or governor?
Final question: On our first coach, a 1997 American Eagle, I did a re-build kit consisting of the purge valve etc and had plenty of room to work under it. Is this something I could accomplish on this H3 bus in our campground / without it being on a lift? Thank you and Safety recommendations appreciated!
-
10 Replies
-
Additional Information… After arriving at our campground, I found it doing the same super-frequent cycling, and after shutting off the engine, I went directly outside and could NOT hear any sounds of leaking air. Thank you again
-
The air system supplies 3 systems. front brakes, rear brakes, and Aux sustem. If the front and rear are holding well, check the aux system. There may be a gauge in the compartment under the drivers seat outside.
-
Sorry – I should have mentioned the aux compressor gauge stays at 120 like the front and rear tank gauges.
-
I don’t think you have a problem at all.
My dryer cycles after all systems are fully pressurized, but I never measured the time between cycles.
If you had a problem such as a big air leak you would see the gauges cycling up and down, but it doesn’t sound like it is doing that.
-
Continued purging of the dryer and no air leaks would point to the purge valve needing rebuilt on the dryer.
-
THANK YOU Jon & Tom
Jon – the strange part is that the pressure on the front and rear tanks never goes below approximately 115 psi, to say approximately 90 psi, then cycles back up to 120 from 90. It just cycles and the air dryer purges every +/- 60 seconds or less
Tom – I will call Haldex technical assistance to see if a re-build kit for this discontinued Haldex dryer is available.
I did do a re-build kit on my first coach’s dryer (also Haldex brand) and was able to have enough room to get under it with all air tanks emptied. Do you think I would be able to get under this H3 in our campground? It just seems lower…If I was at home, I would use the wooden 2″ x 12″ ramps I built…
THANK YOU AGAIN!
-
Check out Bendix trouble shooting guide to help narrow down your problem. I would suspect the air governor, cheap and relatively easy to replace at about $20.
-
The Haldex dryer on your coach has an integral governor. The installation has a supply line for the air compressor, and what appears to be a small line that goes back to the whole coach supply fitting on the rear passenger side coach upright at the rear door hinge side (schrader valve).
It has a line supplying the wet tank.
It has a third small line from the bottom of the dryer assembly going to a small tank, maybe to absorb pressure pulses or whatever. I don’t completely understand the purpose but my point is to describe the lines and fittings.
The air line to the wet tank is always pressurized because there is no check valve between the dryer and wet tank so if the air compressor is cycling due to a loss of pressure it could be related to that or a leak at the fittings or the recycling is absolutely normal. My compressor cycles as you describe. I am unaware of any system leaks to cause that so I just always considered it normal.
I can say we are often oblivious to sounds on our coaches until they come to our attention and then our brain cannot let them go by ignoring them. I have spent a lot of energy chasing noises that were always there, but that I were never fully aware of, until I started hearing them for the first time.
I hate to think how long a window in the living room vibrated and made a noise before I became aware of it, but once I did notice it I was obsessed by it.
1999 XLV X-6872, liberty #440 -
I have noticed this similar issue on our coach for the past year. The Haldex SS1200 air dryer purges every 1 minute. Jeff has replaced nearly every air system component on the coach with no success in correcting this issue. The 1 min cycle is present when the coach is rolling. Chock the wheels with parking brake off & the cycle rate is 15 to 20 minutes. I have driven the coach for over 10,000 miles since noticing the issue. No better or no worse. I am no longer convinced it is a real problem?
Like Jon’s window, this may have always performed in this manner. Once I noticed it I am obsessed by it.
However, Prevost has a service kit to convert the Haldex to a Bendix AD-9 dryer. The significant difference in the dryers is the AD-9 stores its own air for the purge cycle. The SS1200 uses 10psi of air from your wet tank for the purge cycle. This greatly reduces the operating pressure range in the wet tank which reduces the time between cycles.
Good luck
1999 XLV X-6872, liberty #440 -
UPDATE:
After talking to Haldex Tech Support at least three times today, I may have good news to share.
Based upon the symptoms, they believed the frequent purging was the result of an air leak on the “control side” which was defined as “a leak up stream of the primary and secondary air tanks”. The tech added the wet tank was losing pressure.
I next asked him his thoughts concerning the fact the bottom of the dryer produced bubbles when sprayed with soap and water. He immediately said that leak on the dryer itself very likely could be the culprit. He told me to see if the 6 bolts securing the dryer’s “Valve Pak” were loose, and if so, tighten them.
I got blocks of wood to support the chassis and found four of the six allen head bolts were slightly loose and tightened them about 1/8″ of a turn. Re-tested and no bubbles!
So, next, ran engine at high idle and purging occurred three times during 22 minutes of high idle. Once when initially full, then at 2 minutes, then 8 minutes after that, then at 12 minutes after that.
I called tech support back and he said those times were reasonable. We remain in this park until Sunday, so will report back after arrival at our next location.
Here is a link to my very first YouTube video showing the leak prior to tightening the 6 allen head bolts located on the bottom of the dryer.
Log in to reply.