Air Dryer Question

[NJT5047]

Got a problem with my air dryer ejector that may have origins in other than the obvious. 
The problem is an extended purge cycle that lasts about 4 or 5 seconds and then the ejector seals up.

I've ordered an AD2 filter-dryer filter cannister and an ejector rebuild kit.  Also plan to install a new governor.
I replaced the dryer water and oil filter about 4 years ago and have probably driven 5K since.  I check the air tanks occasionally for water and have never had any water or oil in the tanks.  BTW, an awning hook is perfect for reaching under an MC9 to crack the tank drain valves.   

The bus  was dewinterized  last week and the ejector worked correctly for a couple of days before the "fizzie" purge thing started.  Once it started, it has continued with the "fizzies" since.  Not becoming worse, just isn't right. 

An associated issue with the purge valve is that prior to the purge fault, the air would cycle on at about 90+ lbs and cut out at 120 lbs.  Now it's cutting in at slightly less than 90 lbs and cutting out at 115 (or thereabouts).  The pressure change is my rationale for replacing the governor.

My question is what other problems could cause a prolonged purge cycle and the sudden change of compressor cut presures?   Could the gov (D2) cause this sort of prolonged ejector cycle? 

I'm interested in any thoughts on this.   I've got a couple weeks to get this problem fixed.   

Thanks, JR

[Nick Badame Refrig/ACC]

Hi JR,

I would replace the AD2 cartrage first before you go any further.

They can build up some nasty sludge and cause many air system problems.

Good Luck
Nick-

[bevans6]

My understanding, based on reading and observing how my bus air dryer works, is that the purge valve is open on the air dryer all the time that the compressor is not on a fill cycle.  In other words, it opens when the air pressure reaches cut-out pressure causing the governor to cycle, and stays open until the governor sees cut in pressure.  There is a check valve between the air dryer and the wet tank so no pressure is lost.  If you are seeing/hearing a long purge, I would suspect that you need to service the air dryer.  No harm in also servicing the governor.

Brian

[NJT5047]

Thanks guys,

I received a new Bendix filter/oil separator and a purge valve repair kit today.   
All Bendix parts (or labled as such) and detailed install instructions for both.    $83 bucks shipped for both and all of the "O" rings neccessary to install the filter. 
I'll post the outcome.   
I'm not completely sure how it works.  Just that the gov unloader results in a purge cycle. 
I have a description here in an NJT manual.  From what I've read, it seems as though the purge valve closes once a purge cycle is completed....?  I dunno.   
The air system has been dry, and hasn't caused much trouble over the ten years I've used the bus. Probably should know a bit more about how it works...  
It'll be interesting to see how much crud is in the dryer.   I replaced the filter and oil separator about 4 years ago and it wasn't too bad nasty.   No problem with function then.  Just seemed a good idea.   I bought the filters locally last time and I believe the cost was over $100 bucks for the dryer filter only?   

JR
 

[luvrbus]

Jr, the AD 2 has a integral check valve on the outlet if the problem continues it may be bad do some checking the desiccant cartridge should cost about 40 bucks for a rebuilt cartridge for a AD2 Air dryer also fwiw the desiccant material is not that hard to change on the cartridge


good luck

[NJT5047]

Well, I'm a little like the Wizard of Oz's "Straw Man."   If I only had a brain! 
I don't have an AD2, it's an AD9.  DuH!   

JR   

[niles500]

NJT - sorry , if I'd have known it was an AD-9 I would have told you that is a normal purge cycle for the AD-9 - FWIW

[NJT5047]

Thanks Niles, but the sound and duration of the purge valve is different from what it's been.   Having owned and used the coach for 10 years gives me a right good feel for noises, and the air dryer sounds like it's one step from bleeding off the coach. 
Another thing is that until I left for the last trip, it worked with a quick burst of air with purging, and it purged at 120.  Cut in at 90+ lbs.   Now it's lower, like high 80s cut in and 115 cut out.  May not be the dryer, but the only thing on the dryer that's been changed, over ten years,  is the filter.   The purge valve worked then, so it was not molested, and the tanks have always been dry. 
I'm hoping that the dryer repair fixes the problem.  Might not.   I've alread bought a governor and will replace that.  Local sez that the unloader valves will gum up and cause this sort of thing.   
I ordered an NAPA AD9 from NAPA.  No one locally has a 24V unit.  Bummer. 
I don't mind replacing the dryer.  Pretty easy to access.   
I'll post the outcome.   BTW, the nearest 24V AD9 was Missouri?  Won't have it until Wednesday...so they say.
Planning on the KOA Wade (Gene Lewis' BusNuts Rally) the 19th, so I'm anxious to get it repaired.   
Reckon if anyone going to Gene's rally needs a filter and purge valve kit for an AD2, have I got a deal....! 
JR

[NJT5047]

OK.  We have a favourable outcome with the air dryer install.   Fixed the funky purge cycle. 
Now I have one remaining issue to overcome. 
The new air dryer has a special plug for the dryer heater.   My old dryer had a single terminal similar to an automotive water temp sender.   
I've got pix of the thing that I'll post.  If anyone has an idea of where I can find a matching plug for the heater, please advise.   This is one of those piddlin things that ain't worth the time to look for it...but, it needs fixin!
Thanks, JR

[stevet903]

From the picture it looks like a #WPT-2 (12015792)

http://www.whiteproducts.com/connectors.shtml

Steve

[NJT5047]

Thanks for the link and info Steve! Off to see what I can find!   

I'd like to add that as with almost everything "NJT," this wasn't a "bolt-in" install.  The dryer pictured fit, but the whole dryer assembly had to be mounted about 3" higher on the bulkhead than the OEM dryer.  Had to remove the mount and redrill for the new location.  Simple enough, but a lot of work when jammed between the axle and bulkhead!  
Also, in order to raise the dryer, the leveling valve and kneeling valve had to be removed.  These items were not functional, so out they came.   Having to keep the leveling valve would have been problematic.  
I'm not exactly sure how the dryer works, but prior to the repair, the bus had an air leak that I couldn't find.  It was enough that the bus probably wouldn't have passed a DOT inspection.   After replacing the dryer, I aired it up and everything worked.   Shut it down and left if for an hour or so...still reading 118 lbs from an hour earlier.   Don't understand what I'm seeing.  The dryer isn't charged when the air compressor isn't operating (right?).  Are the check valves for the dryer in the dryer base?   Cannot think of any thing else that would have eliminated an air leak.  There are no check valves external to the air dryer...as indicated in the pix.   Any ideas?   The coach air pressure would leak down within an hour to about 60 lbs, and then the leak stopped and it would take days to leak on down from there.


JR

[luvrbus]

That 2 plug dyer has a thermostat (sensor) to to turn the dryer on when it detects cold weather to keep the valve from freezing wired through a relay.
I am checking for a schematic for you the old style 1 wire was on while the engine was running, you need to kill the power or that one or it will drain the batteries coming on in cold weather while sitting  

good luck

[NJT5047]

Thanks for the info!  I'd guess that the temp sensor is inside the dryer base?   I'd guess that it won't matter as  I always take the crank batts out of the circuit within a few minutes of shutdown.   The battery disconnect is always off when the bus isn't being used. 
The "White" connector appears to be correct for an AD-9.  
FWIW, another issue has been resolved.   I didn't have an OEM AD-9 dryer...it was an AD-4, extended purge.      
However, there was no "AD-4" listed as a replacement at NAPA.   Or, I didn't see it listed.  I sorta look up whatever I want.   They may offer it as a special order item?  
Some projects can be so complicated!  

JR

[belfert]

On an AD-9 the thermostat and heater are inside the purge valve assembly.  If you replace the purge valve you're also replacing the heater and thermostat.

[Cary and Don]

Wish we were going to the rally.  That is our next project.  Our AD2 is leaking air and doesn't appear to have been changed since new.


Don and Cary
1973 Eagle
4107 GMC
Neoplan AN340